bitsets for fast checking if a number fits (slower)

.gitignore

@@ -1,2 +1 @@
 /target
-/c_version/sudk_c

Cargo.lock

@@ -4,4 +4,4 @@ version = 3
 
 [[package]]
 name = "sudk"
-version = "0.1.1"
+version = "0.1.0"

Cargo.toml

@@ -1,19 +1,13 @@
 [package]
 name = "sudk"
-version = "0.1.1"
+version = "0.1.0"
 authors = ["ddidderr <ddidderr@paul.network>"]
 edition = "2021"
 
-[lints.clippy]
-pedantic = { level = "warn", priority = -1 }
-todo = "warn"
-unwrap_used = "warn"
-
 [dependencies]
 
 [profile.release]
 lto = true
 debug = false
-strip = true
-panic = "abort"
 codegen-units = 1
+panic = "abort"

c_version/clangtest

@@ -1,6 +0,0 @@
-#!/bin/bash
-set -e
-
-clang -Weverything -Wno-unsafe-buffer-usage -Werror -O3 -march=native -flto -std=c17 -fstack-protector-all -s -o sudk_c "$1"
-
-time ./sudk_c

c_version/gcctest

@@ -1,7 +0,0 @@
-#!/bin/bash
-
-set -e
-
-gcc -Wall -Wextra -Werror --std=c17 -march=native -O3 -fstack-protector-all -flto -s -o sudk_c "$1"
-
-time ./sudk_c

c_version/sudk_lots_of_allocs_for_tmp_rows_cols_blocks.c

@@ -1,287 +0,0 @@
-#include <stdbool.h>
-#include <stddef.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <sys/types.h>
-
-#define PFSALLOC(bytes) malloc(bytes)
-
-static inline void Print_Clear() { printf("\x1b\x5b\x48\x1b\x5b\x32\x4a"); }
-
-typedef struct Sudoku {
-  size_t *field;
-  size_t *fixed;
-  size_t *known;
-  size_t size;
-  size_t block_size;
-  size_t pos;
-  size_t pos_last_placed;
-  size_t num_fields;
-} Sudoku;
-
-static Sudoku *Sudoku_New(size_t block_size) {
-
-  Sudoku *s = calloc(1, sizeof(Sudoku));
-
-  size_t many_solutions_field[81] = {
-      0, 0, 0, 0, 0, 0, 0, 0, 9, 0, 0, 0, 0, 8, 9, 0, 2, 0, 0, 0, 0,
-      0, 2, 0, 4, 0, 0, 0, 0, 4, 0, 6, 0, 0, 0, 8, 0, 0, 0, 5, 0, 0,
-      0, 0, 0, 0, 6, 5, 0, 0, 2, 0, 7, 4, 0, 3, 0, 0, 0, 5, 0, 4, 0,
-      0, 0, 1, 8, 0, 0, 0, 0, 0, 0, 0, 8, 2, 0, 0, 0, 6, 0,
-  };
-
-  size_t size = block_size * block_size;
-  size_t *field = calloc(size * size, sizeof(size_t));
-  size_t *fixed = calloc(size * size, sizeof(size_t));
-  size_t *known = calloc(size * size, sizeof(size_t));
-
-  printf("num_fields: %zu\n", size * size);
-
-  s->field = field;
-  s->fixed = fixed;
-  s->known = known;
-
-  for (size_t idx = 0; idx < 81; idx++) {
-    s->field[idx] = many_solutions_field[idx];
-  }
-
-  for (size_t idx = 0; idx < 81; idx++) {
-    if (s->field[idx] != 0) {
-      s->fixed[idx] = 1;
-      s->known[idx] = 1;
-    }
-  }
-
-  s->size = size;
-  s->block_size = block_size;
-  s->pos = 0;
-  s->pos_last_placed = 0;
-  s->num_fields = size * size;
-
-  return s;
-}
-
-static void Sudoku_Print(Sudoku *s) {
-  for (size_t idx = 0; idx < s->size * s->size; idx++) {
-
-    // newline
-    if (idx != 0 && idx % s->size == 0)
-      printf("\n");
-
-    // nr
-    printf("%zu", s->field[idx]);
-
-    // space
-    if ((idx + 1) % s->size != 0)
-      printf(" ");
-  }
-  printf("\n");
-}
-
-static inline bool Sudoku_Next(Sudoku *s) {
-  if (s->pos == s->num_fields - 1) {
-    /*printf("there is no next\n");*/
-    return false;
-  }
-
-  s->pos++;
-  return true;
-}
-
-static inline bool Sudoku_Prev(Sudoku *s) {
-  if (s->pos == 0)
-    return false;
-
-  s->pos--;
-  return true;
-}
-
-static inline bool Sudoku_IsFixed(Sudoku *s) { return s->fixed[s->pos] == 1; }
-
-static inline size_t Sudoku_GetFieldAtPos(Sudoku *s, size_t pos) {
-  return s->field[pos];
-}
-
-static inline void Sudoku_Set(Sudoku *s, size_t nr) {
-  s->field[s->pos] = nr;
-  s->pos_last_placed = s->pos;
-}
-
-static inline void Sudoku_ClearCurrentField(Sudoku *s) { Sudoku_Set(s, 0); }
-
-/*static void Array_Print(char *name, size_t *arr, size_t len) {*/
-/*printf("%s: ", name);*/
-/*for (size_t idx = 0; idx < len; idx++) {*/
-/*if (idx < len - 1)*/
-/*printf("%zu ", arr[idx]);*/
-/*else*/
-/*printf("%zu", arr[idx]);*/
-/*}*/
-/*printf("\n");*/
-/*}*/
-
-static inline bool Array_Contains(size_t *arr, size_t len, size_t nr) {
-  /*printf("ARRAY_CONTAINS_LEN: %zu\n", len);*/
-  for (size_t idx = 0; idx < len; idx++) {
-    if (arr[idx] == nr) {
-      /*printf("SEARCH FOR %zu --- ", nr);*/
-      /*Array_Print("ARRAY_CONTAINS_TRUE", arr, len);*/
-      return true;
-    }
-  }
-  /*printf("SEARCH FOR %zu --- ", nr);*/
-  /*Array_Print("ARRAY_CONTAINS_FALSE", arr, len);*/
-  return false;
-}
-
-static inline bool Sudoku_IsEnd(Sudoku *s) {
-  return !Array_Contains(s->field, s->num_fields, 0);
-}
-
-static inline bool Sudoku_GotoPrevFreeField(Sudoku *s) {
-  do {
-    if (!Sudoku_IsFixed(s))
-      return true;
-  } while (Sudoku_Prev(s));
-
-  return false;
-}
-
-static inline bool Sudoku_GotoNextFreeField(Sudoku *s) {
-  /*printf("Sudoku_GotoNextFreeField\n");*/
-  do {
-    if (!Sudoku_IsFixed(s))
-      return true;
-  } while (Sudoku_Next(s));
-
-  return false;
-}
-
-static inline size_t *Sudoku_GetRow(Sudoku *s) {
-  size_t *tmp = PFSALLOC(s->size * sizeof(size_t));
-  for (size_t pos = 0; pos < s->size; pos++) {
-    tmp[pos] = Sudoku_GetFieldAtPos(s, (s->pos / s->size) * s->size + pos);
-  }
-  return tmp;
-}
-
-static inline size_t *Sudoku_GetCol(Sudoku *s) {
-  size_t *tmp = PFSALLOC(s->size * sizeof(size_t));
-  for (size_t pos = 0; pos < s->size; pos++) {
-    tmp[pos] = Sudoku_GetFieldAtPos(s, pos * s->size + s->pos % s->size);
-  }
-  return tmp;
-}
-
-static inline size_t *Sudoku_GetBlock(Sudoku *s) {
-  size_t *tmp = PFSALLOC(s->size * sizeof(size_t));
-
-  size_t block_start_row = s->pos / s->size / s->block_size * s->block_size;
-  size_t block_start_col = s->pos % s->size / s->block_size * s->block_size;
-
-  for (size_t r = 0; r < s->block_size; r++) {
-    for (size_t c = 0; c < s->block_size; c++) {
-      tmp[r * s->block_size + c] = Sudoku_GetFieldAtPos(
-          s, s->size * (block_start_row + r) + block_start_col + c);
-    }
-  }
-  return tmp;
-}
-
-static inline bool Sudoku_BlockOk(Sudoku *s, size_t nr) {
-  size_t *block = Sudoku_GetBlock(s);
-  /*Array_Print("BLOCK", block, s->size);*/
-  bool ok = !Array_Contains(block, s->size, nr);
-  return ok;
-}
-
-static inline bool Sudoku_RowOk(Sudoku *s, size_t nr) {
-  size_t *row = Sudoku_GetRow(s);
-  bool ok = !Array_Contains(row, s->size, nr);
-  return ok;
-}
-
-static inline bool Sudoku_ColOk(Sudoku *s, size_t nr) {
-  size_t *col = Sudoku_GetCol(s);
-  bool ok = !Array_Contains(col, s->size, nr);
-  return ok;
-}
-
-static inline bool Sudoku_Ok(Sudoku *s, size_t nr) {
-  return Sudoku_BlockOk(s, nr) && Sudoku_ColOk(s, nr) && Sudoku_RowOk(s, nr);
-}
-
-static inline bool Sudoku_PutValidNr(Sudoku *s) {
-  size_t current_nr = Sudoku_GetFieldAtPos(s, s->pos);
-
-  /*printf("%s() pos=%zu current_nr=%zu\n", __func__, s->pos, current_nr);*/
-
-  for (size_t nr = current_nr; nr < s->size + 1; nr++) {
-    if (Sudoku_Ok(s, nr)) {
-      /*printf("%s() pos=%zu current_nr=%zu nr=%zu\n", __func__, s->pos,*/
-      /*current_nr, nr);*/
-      Sudoku_Set(s, nr);
-      return true;
-    }
-  }
-  return false;
-}
-
-static bool Sudoku_SolveBacktracking(Sudoku *s) {
-  bool found_solution = false;
-  size_t num_solutions = 0;
-  while (1) {
-    /*printf("LOOP: pos=%zu\n", s->pos);*/
-    /*Sudoku_Print(s);*/
-    if (Sudoku_IsEnd(s)) {
-      /*printf("END\n");*/
-      found_solution = true;
-      num_solutions++;
-      if (num_solutions % 100 == 0) {
-        Print_Clear();
-        printf("Solutions: %zu\n", num_solutions);
-        Sudoku_Print(s);
-      }
-
-      if (Sudoku_IsFixed(s)) {
-        /*printf("fixed\n");*/
-        continue;
-      }
-      Sudoku_ClearCurrentField(s);
-      Sudoku_Prev(s);
-      Sudoku_GotoPrevFreeField(s);
-    }
-
-    if (Sudoku_IsFixed(s)) {
-      /*printf("fixed -> goto next\n");*/
-      Sudoku_Next(s);
-      continue;
-    }
-
-    if (Sudoku_GotoNextFreeField(s)) {
-      if (Sudoku_PutValidNr(s)) {
-        Sudoku_Next(s);
-        continue;
-      } else {
-        Sudoku_ClearCurrentField(s);
-        if (!Sudoku_Prev(s)) {
-          printf("Number of solutions: %zu\n", num_solutions);
-          break;
-        }
-        if (!Sudoku_GotoPrevFreeField(s)) {
-          printf("Number of solutions: %zu\n", num_solutions);
-          break;
-        }
-      }
-    }
-  }
-
-  return found_solution;
-}
-
-int main() {
-  Sudoku *s = Sudoku_New(3);
-  Sudoku_Print(s);
-  Sudoku_SolveBacktracking(s);
-  /*Sudoku_Print(s);*/
-}

c_version/sudk_no_alloc_instead_use_global_mut_mem_once_initialized_on_start.c

@@ -1,278 +0,0 @@
-#include <stdbool.h>
-#include <stddef.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <sys/types.h>
-
-static size_t *tmpArr;
-
-static inline void Print_Clear() { printf("\x1b\x5b\x48\x1b\x5b\x32\x4a"); }
-
-typedef struct Sudoku {
-  size_t *field;
-  size_t *fixed;
-  size_t size;
-  size_t block_size;
-  size_t pos;
-  size_t pos_last_placed;
-  size_t num_fields;
-} Sudoku;
-
-static Sudoku *Sudoku_New(size_t block_size) {
-
-  Sudoku *s = calloc(1, sizeof(Sudoku));
-
-  size_t many_solutions_field[81] = {
-      0, 0, 0, 0, 0, 0, 0, 0, 9, 0, 0, 0, 0, 8, 9, 0, 2, 0, 0, 0, 0,
-      0, 2, 0, 4, 0, 0, 0, 0, 4, 0, 6, 0, 0, 0, 8, 0, 0, 0, 5, 0, 0,
-      0, 0, 0, 0, 6, 5, 0, 0, 2, 0, 7, 4, 0, 3, 0, 0, 0, 5, 0, 4, 0,
-      0, 0, 1, 8, 0, 0, 0, 0, 0, 0, 0, 8, 2, 0, 0, 0, 6, 0,
-  };
-
-  size_t size = block_size * block_size;
-  size_t *field = calloc(size * size, sizeof(size_t));
-  size_t *fixed = calloc(size * size, sizeof(size_t));
-
-  printf("num_fields: %zu\n", size * size);
-
-  s->field = field;
-  s->fixed = fixed;
-
-  for (size_t idx = 0; idx < 81; idx++) {
-    s->field[idx] = many_solutions_field[idx];
-  }
-
-  for (size_t idx = 0; idx < 81; idx++) {
-    if (s->field[idx] != 0) {
-      s->fixed[idx] = 1;
-    }
-  }
-
-  s->size = size;
-  s->block_size = block_size;
-  s->pos = 0;
-  s->pos_last_placed = 0;
-  s->num_fields = size * size;
-
-  tmpArr = calloc(s->size, sizeof(size_t));
-
-  return s;
-}
-
-static void Sudoku_Print(Sudoku *s) {
-  for (size_t idx = 0; idx < s->size * s->size; idx++) {
-
-    // newline
-    if (idx != 0 && idx % s->size == 0)
-      printf("\n");
-
-    // nr
-    printf("%zu", s->field[idx]);
-
-    // space
-    if ((idx + 1) % s->size != 0)
-      printf(" ");
-  }
-  printf("\n");
-}
-
-static inline bool Sudoku_Next(Sudoku *s) {
-  if (s->pos == s->num_fields - 1) {
-    /*printf("there is no next\n");*/
-    return false;
-  }
-
-  s->pos++;
-  return true;
-}
-
-static inline bool Sudoku_Prev(Sudoku *s) {
-  if (s->pos == 0)
-    return false;
-
-  s->pos--;
-  return true;
-}
-
-static inline bool Sudoku_IsFixed(Sudoku *s) { return s->fixed[s->pos] == 1; }
-
-static inline size_t Sudoku_GetFieldAtPos(Sudoku *s, size_t pos) {
-  return s->field[pos];
-}
-
-static inline void Sudoku_Set(Sudoku *s, size_t nr) {
-  s->field[s->pos] = nr;
-  s->pos_last_placed = s->pos;
-}
-
-static inline void Sudoku_ClearCurrentField(Sudoku *s) { Sudoku_Set(s, 0); }
-
-static inline bool Array_Contains(size_t *arr, size_t len, size_t nr) {
-  /*printf("ARRAY_CONTAINS_LEN: %zu\n", len);*/
-  for (size_t idx = 0; idx < len; idx++) {
-    if (arr[idx] == nr) {
-      /*printf("SEARCH FOR %zu --- ", nr);*/
-      /*Array_Print("ARRAY_CONTAINS_TRUE", arr, len);*/
-      return true;
-    }
-  }
-  /*printf("SEARCH FOR %zu --- ", nr);*/
-  /*Array_Print("ARRAY_CONTAINS_FALSE", arr, len);*/
-  return false;
-}
-
-static inline bool Sudoku_IsEnd(Sudoku *s) {
-  return !Array_Contains(s->field, s->num_fields, 0);
-}
-
-static inline bool Sudoku_GotoPrevFreeField(Sudoku *s) {
-  do {
-    if (!Sudoku_IsFixed(s))
-      return true;
-  } while (Sudoku_Prev(s));
-
-  return false;
-}
-
-static inline bool Sudoku_GotoNextFreeField(Sudoku *s) {
-  /*printf("Sudoku_GotoNextFreeField\n");*/
-  do {
-    if (!Sudoku_IsFixed(s))
-      return true;
-  } while (Sudoku_Next(s));
-
-  return false;
-}
-
-static inline size_t *Sudoku_GetRow(Sudoku *s) {
-  for (size_t pos = 0; pos < s->size; pos++) {
-    tmpArr[pos] = Sudoku_GetFieldAtPos(s, (s->pos / s->size) * s->size + pos);
-  }
-  return tmpArr;
-}
-
-static inline size_t *Sudoku_GetCol(Sudoku *s) {
-  for (size_t pos = 0; pos < s->size; pos++) {
-    tmpArr[pos] = Sudoku_GetFieldAtPos(s, pos * s->size + s->pos % s->size);
-  }
-  return tmpArr;
-}
-
-static inline size_t *Sudoku_GetBlock(Sudoku *s) {
-  size_t block_start_row = s->pos / s->size / s->block_size * s->block_size;
-  size_t block_start_col = s->pos % s->size / s->block_size * s->block_size;
-
-  for (size_t r = 0; r < s->block_size; r++) {
-    for (size_t c = 0; c < s->block_size; c++) {
-      tmpArr[r * s->block_size + c] = Sudoku_GetFieldAtPos(
-          s, s->size * (block_start_row + r) + block_start_col + c);
-    }
-  }
-  return tmpArr;
-}
-
-static inline bool Sudoku_BlockOk(Sudoku *s, size_t nr) {
-  size_t *block = Sudoku_GetBlock(s);
-  /*Array_Print("BLOCK", block, s->size);*/
-  bool ok = !Array_Contains(block, s->size, nr);
-  return ok;
-}
-
-static inline bool Sudoku_RowOk(Sudoku *s, size_t nr) {
-  size_t *row = Sudoku_GetRow(s);
-  bool ok = !Array_Contains(row, s->size, nr);
-  return ok;
-}
-
-static inline bool Sudoku_ColOk(Sudoku *s, size_t nr) {
-  size_t *col = Sudoku_GetCol(s);
-  bool ok = !Array_Contains(col, s->size, nr);
-  return ok;
-}
-
-static inline bool Sudoku_Ok(Sudoku *s, size_t nr) {
-  return Sudoku_BlockOk(s, nr) && Sudoku_ColOk(s, nr) && Sudoku_RowOk(s, nr);
-}
-
-static inline bool Sudoku_PutValidNr(Sudoku *s) {
-  size_t current_nr = Sudoku_GetFieldAtPos(s, s->pos);
-
-  /*printf("%s() pos=%zu current_nr=%zu\n", __func__, s->pos, current_nr);*/
-
-  for (size_t nr = current_nr; nr < s->size + 1; nr++) {
-    if (Sudoku_Ok(s, nr)) {
-      /*printf("%s() pos=%zu current_nr=%zu nr=%zu\n", __func__, s->pos,*/
-      /*current_nr, nr);*/
-      Sudoku_Set(s, nr);
-      return true;
-    }
-  }
-  return false;
-}
-
-static bool Sudoku_SolveBacktracking(Sudoku *s) {
-  bool found_solution = false;
-  size_t num_solutions = 0;
-  while (1) {
-    /*printf("LOOP: pos=%zu\n", s->pos);*/
-    /*Sudoku_Print(s);*/
-    if (Sudoku_IsEnd(s)) {
-      /*printf("END\n");*/
-      found_solution = true;
-      num_solutions++;
-      if (num_solutions % 100 == 0) {
-        Print_Clear();
-        printf("Solutions: %zu\n", num_solutions);
-        Sudoku_Print(s);
-      }
-
-      if (Sudoku_IsFixed(s)) {
-        /*printf("fixed\n");*/
-        continue;
-      }
-      Sudoku_ClearCurrentField(s);
-      Sudoku_Prev(s);
-      Sudoku_GotoPrevFreeField(s);
-    }
-
-    if (Sudoku_IsFixed(s)) {
-      /*printf("fixed -> goto next\n");*/
-      Sudoku_Next(s);
-      continue;
-    }
-
-    if (Sudoku_GotoNextFreeField(s)) {
-      if (Sudoku_PutValidNr(s)) {
-        Sudoku_Next(s);
-        continue;
-      } else {
-        Sudoku_ClearCurrentField(s);
-        if (!Sudoku_Prev(s)) {
-          printf("Number of solutions: %zu\n", num_solutions);
-          break;
-        }
-        if (!Sudoku_GotoPrevFreeField(s)) {
-          printf("Number of solutions: %zu\n", num_solutions);
-          break;
-        }
-      }
-    }
-  }
-
-  return found_solution;
-}
-
-static void Sudoku_Free(Sudoku *s) {
-  free(s->field);
-  free(s->fixed);
-  free(s);
-  s = NULL;
-}
-
-int main() {
-  Sudoku *s = Sudoku_New(3);
-  Sudoku_Print(s);
-  Sudoku_SolveBacktracking(s);
-  Sudoku_Free(s);
-  free(tmpArr);
-}

c_version/sudk_stack.c

@@ -1,266 +0,0 @@
-#include <stdbool.h>
-#include <stddef.h>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <sys/types.h>
-
-static inline void Print_Clear(void) { printf("\x1b\x5b\x48\x1b\x5b\x32\x4a"); }
-
-typedef struct Sudoku {
-  uint8_t *field;
-  bool *fixed;
-  size_t size;
-  size_t block_size;
-  size_t pos;
-  size_t pos_last_placed;
-  size_t num_fields;
-} Sudoku;
-
-static Sudoku *Sudoku_New(size_t block_size) {
-
-  Sudoku *s = calloc(1, sizeof(Sudoku));
-
-  // clang-format off
-  uint8_t many_solutions_field[81] = {
-      0, 0, 0, 0, 0, 0, 0, 0, 9,
-      0, 0, 0, 0, 8, 9, 0, 2, 0,
-      0, 0, 0, 0, 2, 0, 4, 0, 0,
-      0, 0, 4, 0, 6, 0, 0, 0, 8,
-      0, 0, 0, 5, 0, 0, 0, 0, 0,
-      0, 6, 5, 0, 0, 2, 0, 7, 4,
-      0, 3, 0, 0, 0, 5, 0, 4, 0,
-      0, 0, 1, 8, 0, 0, 0, 0, 0,
-      0, 0, 8, 2, 0, 0, 0, 6, 0,
-  };
-  // clang-format on
-
-  size_t size = block_size * block_size;
-  uint8_t *field = calloc(size * size, sizeof(uint8_t));
-  bool *fixed = calloc(size * size, sizeof(bool));
-
-  printf("num_fields: %zu\n", size * size);
-
-  s->field = field;
-  s->fixed = fixed;
-
-  for (size_t idx = 0; idx < 81; idx++) {
-    s->field[idx] = many_solutions_field[idx];
-  }
-
-  for (size_t idx = 0; idx < 81; idx++) {
-    if (s->field[idx] != 0) {
-      s->fixed[idx] = true;
-    }
-  }
-
-  s->size = size;
-  s->block_size = block_size;
-  s->pos = 0;
-  s->pos_last_placed = 0;
-  s->num_fields = size * size;
-
-  return s;
-}
-
-static inline void Sudoku_Print(Sudoku *s) {
-  for (size_t idx = 0; idx < s->num_fields; idx++) {
-
-    // newline
-    if (idx != 0 && idx % s->size == 0)
-      printf("\n");
-
-    // nr
-    printf("%hhu", s->field[idx]);
-
-    // space
-    if ((idx + 1) % s->size != 0)
-      printf(" ");
-  }
-  printf("\n");
-}
-
-static inline bool Sudoku_Next(Sudoku *s) {
-  if (s->pos == s->num_fields - 1) {
-    return false;
-  }
-
-  s->pos++;
-  return true;
-}
-
-static inline bool Sudoku_Prev(Sudoku *s) {
-  if (s->pos == 0)
-    return false;
-
-  s->pos--;
-  return true;
-}
-
-static inline bool Sudoku_IsFixed(Sudoku *s) { return s->fixed[s->pos]; }
-
-static inline uint8_t Sudoku_GetFieldAtPos(Sudoku *s, size_t pos) {
-  return s->field[pos];
-}
-
-static inline void Sudoku_Set(Sudoku *s, uint8_t nr) {
-  s->field[s->pos] = nr;
-  s->pos_last_placed = s->pos;
-}
-
-static inline void Sudoku_ClearCurrentField(Sudoku *s) { Sudoku_Set(s, 0); }
-
-static inline bool Array_Contains(uint8_t *arr, size_t len, uint8_t nr) {
-  for (size_t idx = 0; idx < len; idx++) {
-    if (arr[idx] == nr) {
-      return true;
-    }
-  }
-  return false;
-}
-
-static inline bool Sudoku_IsEnd(Sudoku *s) {
-  return !Array_Contains(s->field, s->num_fields, 0);
-}
-
-static inline bool Sudoku_GotoPrevFreeField(Sudoku *s) {
-  do {
-    if (!Sudoku_IsFixed(s))
-      return true;
-  } while (Sudoku_Prev(s));
-
-  return false;
-}
-
-static inline bool Sudoku_GotoNextFreeField(Sudoku *s) {
-  do {
-    if (!Sudoku_IsFixed(s))
-      return true;
-  } while (Sudoku_Next(s));
-
-  return false;
-}
-
-static inline void Sudoku_GetRow(Sudoku *s, uint8_t *row) {
-  for (size_t pos = 0; pos < s->size; pos++) {
-    row[pos] = Sudoku_GetFieldAtPos(s, (s->pos / s->size) * s->size + pos);
-  }
-}
-
-static inline void Sudoku_GetCol(Sudoku *s, uint8_t *col) {
-  for (size_t pos = 0; pos < s->size; pos++) {
-    col[pos] = Sudoku_GetFieldAtPos(s, pos * s->size + s->pos % s->size);
-  }
-}
-
-static inline void Sudoku_GetBlock(Sudoku *s, uint8_t *block) {
-  size_t block_start_row = s->pos / s->size / s->block_size * s->block_size;
-  size_t block_start_col = s->pos % s->size / s->block_size * s->block_size;
-
-  for (size_t r = 0; r < s->block_size; r++) {
-    for (size_t c = 0; c < s->block_size; c++) {
-      block[r * s->block_size + c] = Sudoku_GetFieldAtPos(
-          s, s->size * (block_start_row + r) + block_start_col + c);
-    }
-  }
-}
-
-static inline bool Sudoku_BlockOk(Sudoku *s, uint8_t nr) {
-  bool ok;
-  uint8_t block[9] = {0};
-  Sudoku_GetBlock(s, block);
-  ok = !Array_Contains(block, s->size, nr);
-  return ok;
-}
-
-static inline bool Sudoku_RowOk(Sudoku *s, uint8_t nr) {
-  bool ok;
-  uint8_t row[9] = {0};
-  Sudoku_GetRow(s, row);
-  ok = !Array_Contains(row, s->size, nr);
-  return ok;
-}
-
-static inline bool Sudoku_ColOk(Sudoku *s, uint8_t nr) {
-  bool ok;
-  uint8_t col[9] = {0};
-  Sudoku_GetCol(s, col);
-  ok = !Array_Contains(col, s->size, nr);
-  return ok;
-}
-
-static inline bool Sudoku_Ok(Sudoku *s, uint8_t nr) {
-  return Sudoku_BlockOk(s, nr) && Sudoku_ColOk(s, nr) && Sudoku_RowOk(s, nr);
-}
-
-static inline bool Sudoku_PutValidNr(Sudoku *s) {
-  uint8_t current_nr = Sudoku_GetFieldAtPos(s, s->pos);
-  for (uint8_t nr = current_nr; nr < s->size + 1; nr++) {
-    if (Sudoku_Ok(s, nr)) {
-      Sudoku_Set(s, nr);
-      return true;
-    }
-  }
-  return false;
-}
-
-static bool Sudoku_SolveBacktracking(Sudoku *s) {
-  bool found_solution = false;
-  size_t num_solutions = 0;
-  while (1) {
-    if (Sudoku_IsEnd(s)) {
-      found_solution = true;
-      num_solutions++;
-      if (num_solutions % 100 == 0) {
-        Print_Clear();
-        printf("Solutions: %zu\n", num_solutions);
-        Sudoku_Print(s);
-      }
-
-      if (Sudoku_IsFixed(s)) {
-        continue;
-      }
-      Sudoku_ClearCurrentField(s);
-      Sudoku_Prev(s);
-      Sudoku_GotoPrevFreeField(s);
-    }
-
-    if (Sudoku_IsFixed(s)) {
-      Sudoku_Next(s);
-      continue;
-    }
-
-    if (Sudoku_GotoNextFreeField(s)) {
-      if (Sudoku_PutValidNr(s)) {
-        Sudoku_Next(s);
-        continue;
-      } else {
-        Sudoku_ClearCurrentField(s);
-        if (!Sudoku_Prev(s)) {
-          printf("Number of solutions: %zu\n", num_solutions);
-          break;
-        }
-        if (!Sudoku_GotoPrevFreeField(s)) {
-          printf("Number of solutions: %zu\n", num_solutions);
-          break;
-        }
-      }
-    }
-  }
-
-  return found_solution;
-}
-
-static void Sudoku_Free(Sudoku *s) {
-  free(s->field);
-  free(s->fixed);
-  free(s);
-  s = NULL;
-}
-
-int main(void) {
-  Sudoku *s = Sudoku_New(3);
-  Sudoku_Print(s);
-  Sudoku_SolveBacktracking(s);
-  Sudoku_Free(s);
-}

flamegraph.svg

@@ -1,491 +0,0 @@
-<?xml version="1.0" standalone="no"?><!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"><svg version="1.1" width="1200" height="374" onload="init(evt)" viewBox="0 0 1200 374" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:fg="http://github.com/jonhoo/inferno"><!--Flame graph stack visualization. See https://github.com/brendangregg/FlameGraph for latest version, and http://www.brendangregg.com/flamegraphs.html for examples.--><!--NOTES: --><defs><linearGradient id="background" y1="0" y2="1" x1="0" x2="0"><stop stop-color="#eeeeee" offset="5%"/><stop stop-color="#eeeeb0" offset="95%"/></linearGradient></defs><style type="text/css">
-text { font-family:monospace; font-size:12px }
-#title { text-anchor:middle; font-size:17px; }
-#matched { text-anchor:end; }
-#search { text-anchor:end; opacity:0.1; cursor:pointer; }
-#search:hover, #search.show { opacity:1; }
-#subtitle { text-anchor:middle; font-color:rgb(160,160,160); }
-#unzoom { cursor:pointer; }
-#frames > *:hover { stroke:black; stroke-width:0.5; cursor:pointer; }
-.hide { display:none; }
-.parent { opacity:0.5; }
-</style><script type="text/ecmascript"><![CDATA[
-        var nametype = 'Function:';
-        var fontsize = 12;
-        var fontwidth = 0.59;
-        var xpad = 10;
-        var inverted = false;
-        var searchcolor = 'rgb(230,0,230)';
-        var fluiddrawing = true;
-        var truncate_text_right = false;
-    ]]><![CDATA["use strict";
-var details, searchbtn, unzoombtn, matchedtxt, svg, searching, frames, known_font_width;
-function init(evt) {
-    details = document.getElementById("details").firstChild;
-    searchbtn = document.getElementById("search");
-    unzoombtn = document.getElementById("unzoom");
-    matchedtxt = document.getElementById("matched");
-    svg = document.getElementsByTagName("svg")[0];
-    frames = document.getElementById("frames");
-    known_font_width = get_monospace_width(frames);
-    total_samples = parseInt(frames.attributes.total_samples.value);
-    searching = 0;
-
-    // Use GET parameters to restore a flamegraph's state.
-    var restore_state = function() {
-        var params = get_params();
-        if (params.x && params.y)
-            zoom(find_group(document.querySelector('[*|x="' + params.x + '"][y="' + params.y + '"]')));
-        if (params.s)
-            search(params.s);
-    };
-
-    if (fluiddrawing) {
-        // Make width dynamic so the SVG fits its parent's width.
-        svg.removeAttribute("width");
-        // Edge requires us to have a viewBox that gets updated with size changes.
-        var isEdge = /Edge\/\d./i.test(navigator.userAgent);
-        if (!isEdge) {
-            svg.removeAttribute("viewBox");
-        }
-        var update_for_width_change = function() {
-            if (isEdge) {
-                svg.attributes.viewBox.value = "0 0 " + svg.width.baseVal.value + " " + svg.height.baseVal.value;
-            }
-
-            // Keep consistent padding on left and right of frames container.
-            frames.attributes.width.value = svg.width.baseVal.value - xpad * 2;
-
-            // Text truncation needs to be adjusted for the current width.
-            update_text_for_elements(frames.children);
-
-            // Keep search elements at a fixed distance from right edge.
-            var svgWidth = svg.width.baseVal.value;
-            searchbtn.attributes.x.value = svgWidth - xpad;
-            matchedtxt.attributes.x.value = svgWidth - xpad;
-        };
-        window.addEventListener('resize', function() {
-            update_for_width_change();
-        });
-        // This needs to be done asynchronously for Safari to work.
-        setTimeout(function() {
-            unzoom();
-            update_for_width_change();
-            restore_state();
-        }, 0);
-    } else {
-        restore_state();
-    }
-}
-// event listeners
-window.addEventListener("click", function(e) {
-    var target = find_group(e.target);
-    if (target) {
-        if (target.nodeName == "a") {
-            if (e.ctrlKey === false) return;
-            e.preventDefault();
-        }
-        if (target.classList.contains("parent")) unzoom();
-        zoom(target);
-
-        // set parameters for zoom state
-        var el = target.querySelector("rect");
-        if (el && el.attributes && el.attributes.y && el.attributes["fg:x"]) {
-            var params = get_params()
-            params.x = el.attributes["fg:x"].value;
-            params.y = el.attributes.y.value;
-            history.replaceState(null, null, parse_params(params));
-        }
-    }
-    else if (e.target.id == "unzoom") {
-        unzoom();
-
-        // remove zoom state
-        var params = get_params();
-        if (params.x) delete params.x;
-        if (params.y) delete params.y;
-        history.replaceState(null, null, parse_params(params));
-    }
-    else if (e.target.id == "search") search_prompt();
-}, false)
-// mouse-over for info
-// show
-window.addEventListener("mouseover", function(e) {
-    var target = find_group(e.target);
-    if (target) details.nodeValue = nametype + " " + g_to_text(target);
-}, false)
-// clear
-window.addEventListener("mouseout", function(e) {
-    var target = find_group(e.target);
-    if (target) details.nodeValue = ' ';
-}, false)
-// ctrl-F for search
-window.addEventListener("keydown",function (e) {
-    if (e.keyCode === 114 || (e.ctrlKey && e.keyCode === 70)) {
-        e.preventDefault();
-        search_prompt();
-    }
-}, false)
-// functions
-function get_params() {
-    var params = {};
-    var paramsarr = window.location.search.substr(1).split('&');
-    for (var i = 0; i < paramsarr.length; ++i) {
-        var tmp = paramsarr[i].split("=");
-        if (!tmp[0] || !tmp[1]) continue;
-        params[tmp[0]]  = decodeURIComponent(tmp[1]);
-    }
-    return params;
-}
-function parse_params(params) {
-    var uri = "?";
-    for (var key in params) {
-        uri += key + '=' + encodeURIComponent(params[key]) + '&';
-    }
-    if (uri.slice(-1) == "&")
-        uri = uri.substring(0, uri.length - 1);
-    if (uri == '?')
-        uri = window.location.href.split('?')[0];
-    return uri;
-}
-function find_child(node, selector) {
-    var children = node.querySelectorAll(selector);
-    if (children.length) return children[0];
-    return;
-}
-function find_group(node) {
-    var parent = node.parentElement;
-    if (!parent) return;
-    if (parent.id == "frames") return node;
-    return find_group(parent);
-}
-function orig_save(e, attr, val) {
-    if (e.attributes["fg:orig_" + attr] != undefined) return;
-    if (e.attributes[attr] == undefined) return;
-    if (val == undefined) val = e.attributes[attr].value;
-    e.setAttribute("fg:orig_" + attr, val);
-}
-function orig_load(e, attr) {
-    if (e.attributes["fg:orig_"+attr] == undefined) return;
-    e.attributes[attr].value = e.attributes["fg:orig_" + attr].value;
-    e.removeAttribute("fg:orig_" + attr);
-}
-function g_to_text(e) {
-    var text = find_child(e, "title").firstChild.nodeValue;
-    return (text)
-}
-function g_to_func(e) {
-    var func = g_to_text(e);
-    // if there's any manipulation we want to do to the function
-    // name before it's searched, do it here before returning.
-    return (func);
-}
-function get_monospace_width(frames) {
-    // Given the id="frames" element, return the width of text characters if
-    // this is a monospace font, otherwise return 0.
-    text = find_child(frames.children[0], "text");
-    originalContent = text.textContent;
-    text.textContent = "!";
-    bangWidth = text.getComputedTextLength();
-    text.textContent = "W";
-    wWidth = text.getComputedTextLength();
-    text.textContent = originalContent;
-    if (bangWidth === wWidth) {
-        return bangWidth;
-    } else {
-        return 0;
-    }
-}
-function update_text_for_elements(elements) {
-    // In order to render quickly in the browser, you want to do one pass of
-    // reading attributes, and one pass of mutating attributes. See
-    // https://web.dev/avoid-large-complex-layouts-and-layout-thrashing/ for details.
-
-    // Fall back to inefficient calculation, if we're variable-width font.
-    // TODO This should be optimized somehow too.
-    if (known_font_width === 0) {
-        for (var i = 0; i < elements.length; i++) {
-            update_text(elements[i]);
-        }
-        return;
-    }
-
-    var textElemNewAttributes = [];
-    for (var i = 0; i < elements.length; i++) {
-        var e = elements[i];
-        var r = find_child(e, "rect");
-        var t = find_child(e, "text");
-        var w = parseFloat(r.attributes.width.value) * frames.attributes.width.value / 100 - 3;
-        var txt = find_child(e, "title").textContent.replace(/\([^(]*\)$/,"");
-        var newX = format_percent((parseFloat(r.attributes.x.value) + (100 * 3 / frames.attributes.width.value)));
-
-        // Smaller than this size won't fit anything
-        if (w < 2 * known_font_width) {
-            textElemNewAttributes.push([newX, ""]);
-            continue;
-        }
-
-        // Fit in full text width
-        if (txt.length * known_font_width < w) {
-            textElemNewAttributes.push([newX, txt]);
-            continue;
-        }
-
-        var substringLength = Math.floor(w / known_font_width) - 2;
-        if (truncate_text_right) {
-            // Truncate the right side of the text.
-            textElemNewAttributes.push([newX, txt.substring(0, substringLength) + ".."]);
-            continue;
-        } else {
-            // Truncate the left side of the text.
-            textElemNewAttributes.push([newX, ".." + txt.substring(txt.length - substringLength, txt.length)]);
-            continue;
-        }
-    }
-
-    console.assert(textElemNewAttributes.length === elements.length, "Resize failed, please file a bug at https://github.com/jonhoo/inferno/");
-
-    // Now that we know new textContent, set it all in one go so we don't refresh a bazillion times.
-    for (var i = 0; i < elements.length; i++) {
-        var e = elements[i];
-        var values = textElemNewAttributes[i];
-        var t = find_child(e, "text");
-        t.attributes.x.value = values[0];
-        t.textContent = values[1];
-    }
-}
-
-function update_text(e) {
-    var r = find_child(e, "rect");
-    var t = find_child(e, "text");
-    var w = parseFloat(r.attributes.width.value) * frames.attributes.width.value / 100 - 3;
-    var txt = find_child(e, "title").textContent.replace(/\([^(]*\)$/,"");
-    t.attributes.x.value = format_percent((parseFloat(r.attributes.x.value) + (100 * 3 / frames.attributes.width.value)));
-
-    // Smaller than this size won't fit anything
-    if (w < 2 * fontsize * fontwidth) {
-        t.textContent = "";
-        return;
-    }
-    t.textContent = txt;
-    // Fit in full text width
-    if (t.getComputedTextLength() < w)
-        return;
-    if (truncate_text_right) {
-        // Truncate the right side of the text.
-        for (var x = txt.length - 2; x > 0; x--) {
-            if (t.getSubStringLength(0, x + 2) <= w) {
-                t.textContent = txt.substring(0, x) + "..";
-                return;
-            }
-        }
-    } else {
-        // Truncate the left side of the text.
-        for (var x = 2; x < txt.length; x++) {
-            if (t.getSubStringLength(x - 2, txt.length) <= w) {
-                t.textContent = ".." + txt.substring(x, txt.length);
-                return;
-            }
-        }
-    }
-    t.textContent = "";
-}
-// zoom
-function zoom_reset(e) {
-    if (e.tagName == "rect") {
-        e.attributes.x.value = format_percent(100 * parseInt(e.attributes["fg:x"].value) / total_samples);
-        e.attributes.width.value = format_percent(100 * parseInt(e.attributes["fg:w"].value) / total_samples);
-    }
-    if (e.childNodes == undefined) return;
-    for(var i = 0, c = e.childNodes; i < c.length; i++) {
-        zoom_reset(c[i]);
-    }
-}
-function zoom_child(e, x, zoomed_width_samples) {
-    if (e.tagName == "text") {
-        var parent_x = parseFloat(find_child(e.parentNode, "rect[x]").attributes.x.value);
-        e.attributes.x.value = format_percent(parent_x + (100 * 3 / frames.attributes.width.value));
-    } else if (e.tagName == "rect") {
-        e.attributes.x.value = format_percent(100 * (parseInt(e.attributes["fg:x"].value) - x) / zoomed_width_samples);
-        e.attributes.width.value = format_percent(100 * parseInt(e.attributes["fg:w"].value) / zoomed_width_samples);
-    }
-    if (e.childNodes == undefined) return;
-    for(var i = 0, c = e.childNodes; i < c.length; i++) {
-        zoom_child(c[i], x, zoomed_width_samples);
-    }
-}
-function zoom_parent(e) {
-    if (e.attributes) {
-        if (e.attributes.x != undefined) {
-            e.attributes.x.value = "0.0%";
-        }
-        if (e.attributes.width != undefined) {
-            e.attributes.width.value = "100.0%";
-        }
-    }
-    if (e.childNodes == undefined) return;
-    for(var i = 0, c = e.childNodes; i < c.length; i++) {
-        zoom_parent(c[i]);
-    }
-}
-function zoom(node) {
-    var attr = find_child(node, "rect").attributes;
-    var width = parseInt(attr["fg:w"].value);
-    var xmin = parseInt(attr["fg:x"].value);
-    var xmax = xmin + width;
-    var ymin = parseFloat(attr.y.value);
-    unzoombtn.classList.remove("hide");
-    var el = frames.children;
-    var to_update_text = [];
-    for (var i = 0; i < el.length; i++) {
-        var e = el[i];
-        var a = find_child(e, "rect").attributes;
-        var ex = parseInt(a["fg:x"].value);
-        var ew = parseInt(a["fg:w"].value);
-        // Is it an ancestor
-        if (!inverted) {
-            var upstack = parseFloat(a.y.value) > ymin;
-        } else {
-            var upstack = parseFloat(a.y.value) < ymin;
-        }
-        if (upstack) {
-            // Direct ancestor
-            if (ex <= xmin && (ex+ew) >= xmax) {
-                e.classList.add("parent");
-                zoom_parent(e);
-                to_update_text.push(e);
-            }
-            // not in current path
-            else
-                e.classList.add("hide");
-        }
-        // Children maybe
-        else {
-            // no common path
-            if (ex < xmin || ex >= xmax) {
-                e.classList.add("hide");
-            }
-            else {
-                zoom_child(e, xmin, width);
-                to_update_text.push(e);
-            }
-        }
-    }
-    update_text_for_elements(to_update_text);
-}
-function unzoom() {
-    unzoombtn.classList.add("hide");
-    var el = frames.children;
-    for(var i = 0; i < el.length; i++) {
-        el[i].classList.remove("parent");
-        el[i].classList.remove("hide");
-        zoom_reset(el[i]);
-    }
-    update_text_for_elements(el);
-}
-// search
-function reset_search() {
-    var el = document.querySelectorAll("#frames rect");
-    for (var i = 0; i < el.length; i++) {
-        orig_load(el[i], "fill")
-    }
-    var params = get_params();
-    delete params.s;
-    history.replaceState(null, null, parse_params(params));
-}
-function search_prompt() {
-    if (!searching) {
-        var term = prompt("Enter a search term (regexp " +
-            "allowed, eg: ^ext4_)", "");
-        if (term != null) {
-            search(term)
-        }
-    } else {
-        reset_search();
-        searching = 0;
-        searchbtn.classList.remove("show");
-        searchbtn.firstChild.nodeValue = "Search"
-        matchedtxt.classList.add("hide");
-        matchedtxt.firstChild.nodeValue = ""
-    }
-}
-function search(term) {
-    var re = new RegExp(term);
-    var el = frames.children;
-    var matches = new Object();
-    var maxwidth = 0;
-    for (var i = 0; i < el.length; i++) {
-        var e = el[i];
-        // Skip over frames which are either not visible, or below the zoomed-to frame
-        if (e.classList.contains("hide") || e.classList.contains("parent")) {
-            continue;
-        }
-        var func = g_to_func(e);
-        var rect = find_child(e, "rect");
-        if (func == null || rect == null)
-            continue;
-        // Save max width. Only works as we have a root frame
-        var w = parseInt(rect.attributes["fg:w"].value);
-        if (w > maxwidth)
-            maxwidth = w;
-        if (func.match(re)) {
-            // highlight
-            var x = parseInt(rect.attributes["fg:x"].value);
-            orig_save(rect, "fill");
-            rect.attributes.fill.value = searchcolor;
-            // remember matches
-            if (matches[x] == undefined) {
-                matches[x] = w;
-            } else {
-                if (w > matches[x]) {
-                    // overwrite with parent
-                    matches[x] = w;
-                }
-            }
-            searching = 1;
-        }
-    }
-    if (!searching)
-        return;
-    var params = get_params();
-    params.s = term;
-    history.replaceState(null, null, parse_params(params));
-
-    searchbtn.classList.add("show");
-    searchbtn.firstChild.nodeValue = "Reset Search";
-    // calculate percent matched, excluding vertical overlap
-    var count = 0;
-    var lastx = -1;
-    var lastw = 0;
-    var keys = Array();
-    for (k in matches) {
-        if (matches.hasOwnProperty(k))
-            keys.push(k);
-    }
-    // sort the matched frames by their x location
-    // ascending, then width descending
-    keys.sort(function(a, b){
-        return a - b;
-    });
-    // Step through frames saving only the biggest bottom-up frames
-    // thanks to the sort order. This relies on the tree property
-    // where children are always smaller than their parents.
-    for (var k in keys) {
-        var x = parseInt(keys[k]);
-        var w = matches[keys[k]];
-        if (x >= lastx + lastw) {
-            count += w;
-            lastx = x;
-            lastw = w;
-        }
-    }
-    // display matched percent
-    matchedtxt.classList.remove("hide");
-    var pct = 100 * count / maxwidth;
-    if (pct != 100) pct = pct.toFixed(1);
-    matchedtxt.firstChild.nodeValue = "Matched: " + pct + "%";
-}
-function format_percent(n) {
-    return n.toFixed(4) + "%";
-}
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rustfmt.toml

@@ -1,3 +0,0 @@
-group_imports = "StdExternalCrate"
-imports_granularity = "Crate"
-imports_layout = "HorizontalVertical"

src/main.rs

@@ -1,114 +1,249 @@
 use std::time::Instant;
 
-const BLOCK_SIZE: usize = 3;
+#[derive(Copy, Clone, Debug)]
-const SIZE: usize = BLOCK_SIZE * BLOCK_SIZE;
+struct Bitset {
-const NUM_FIELDS: usize = SIZE * SIZE;
+    set: u16,
-
-fn print_gray() {
-    print!("\x1b\x5b\x31\x3b\x33\x30\x6d");
 }
 
-fn print_green() {
+impl Bitset {
-    print!("\x1b\x5b\x31\x3b\x33\x32\x6d");
+    pub fn new() -> Self {
+        Self { set: 0 }
+    }
+
+    #[inline(always)]
+    fn get(&self, nr: usize) -> bool {
+        self.set & (1 << nr) != 0
+    }
+
+    #[inline(always)]
+    fn set(&mut self, nr: usize) {
+        self.set |= 1 << nr;
+    }
+
+    #[inline(always)]
+    fn unset(&mut self, nr: usize) {
+        self.set &= !(1 << nr);
+    }
 }
 
-fn print_neutral() {
+const BLOCK_SIZE: usize = 4;
-    print!("\x1b\x5b\x31\x3b\x30\x6d");
+//const MAX_BLOCK_SIZE: usize = 10;
-}
-
-fn print_clear() {
-    print!("\x1b\x5b\x48\x1b\x5b\x32\x4a");
-}
 
 struct SField {
-    field: Vec<u8>,
+    field: Vec<usize>,
-    skip_forward: Vec<u8>,
+    fixed: Vec<usize>,
-    skip_backward: Vec<u8>,
+    size: usize,
     pos: usize,
-    possible_values: Vec<Vec<u8>>,
+    pos_last_placed: usize,
+    num_fields: usize,
+    possible_values: Vec<Vec<usize>>,
+
+    // For each row/col/block we create a bitset that represents the numbers
+    // that are already in that row, col or block.
+    // This way we can check very fast if a nr fits into a specific field or not.
+    rows: [Bitset; BLOCK_SIZE * BLOCK_SIZE],
+    cols: [Bitset; BLOCK_SIZE * BLOCK_SIZE],
+    blocks: [Bitset; BLOCK_SIZE * BLOCK_SIZE],
+}
+
+#[inline(always)]
+fn xy_to_pos(x: usize, y: usize, size: usize) -> usize {
+    y * size + x
+}
+
+#[inline(always)]
+fn pos_to_xy_blocknr(pos: usize, size: usize) -> (usize, usize, usize) {
+    let x = pos % size;
+    let y = pos / size;
+
+    let block_x = x / BLOCK_SIZE;
+    let block_y = y / BLOCK_SIZE;
+
+    let block_nr = block_y * BLOCK_SIZE + block_x;
+
+    (x, y, block_nr)
 }
 
 impl SField {
     pub fn new() -> SField {
-        #[rustfmt::skip]
+        const SIZE: usize = BLOCK_SIZE * BLOCK_SIZE;
-        let field = vec![
-            0,0,0,0,0,0,0,0,0,
-            0,0,0,0,8,9,0,0,0,
-            0,0,0,0,2,0,4,0,0,
-            0,0,4,0,6,0,0,0,8,
-            0,0,0,5,0,0,0,0,0,
-            0,6,5,0,0,2,0,7,4,
-            0,3,0,0,0,5,0,4,0,
-            0,0,1,8,0,0,0,0,0,
-            0,0,8,2,0,0,0,6,0,
-        ];
 
-        let mut sudoku = SField {
+        // EMPTY FIELD
-            field,
+        // let field = vec![0; size * size];
-            skip_forward: vec![0; NUM_FIELDS + 1],
+
-            skip_backward: vec![0; NUM_FIELDS + 1],
+        #[rustfmt::skip]
-            pos: 0,
+        let field = match BLOCK_SIZE {
-            possible_values: vec![vec![]; NUM_FIELDS],
+            4 => vec![
+                0usize,15,0,0,0,0,11,4,0,5,0,0,0,0,12,8,
+                12,0,0,9,0,1,0,5,0,0,8,15,0,0,0,13,
+                0,0,3,0,0,10,13,0,0,11,4,0,15,0,6,0,
+                13,10,0,11,0,0,0,14,0,3,2,0,0,9,0,0,
+                0,0,15,10,8,0,0,0,0,0,14,0,0,6,2,0,
+                0,0,14,0,0,0,6,0,0,0,0,0,1,0,0,0,
+                0,11,0,8,3,0,15,1,6,0,0,0,0,0,0,7,
+                0,6,0,7,0,0,0,0,8,13,0,0,10,0,0,0,
+                0,14,0,2,0,0,0,0,3,0,5,0,11,15,9,0,
+                0,0,0,12,11,0,2,0,0,0,0,0,0,0,0,0,
+                0,8,0,0,6,14,1,0,13,15,0,0,0,0,0,10,
+                10,0,0,3,9,0,7,0,0,1,0,0,13,12,8,0,
+                7,0,0,0,0,0,14,0,0,0,0,0,0,0,0,9,
+                0,3,0,14,0,0,9,6,0,0,0,0,0,4,0,0,
+                0,4,6,0,0,7,0,0,0,0,0,0,0,0,0,0,
+                5,2,0,0,0,4,10,15,1,0,3,0,0,0,7,0,
+            ],
+            3 => vec![
+                0,0,0,0,0,0,0,0,9,
+                0,0,0,0,8,9,0,2,0,
+                0,0,0,0,2,0,4,0,0,
+                0,0,4,0,6,0,0,0,8,
+                0,0,0,5,0,0,0,0,0,
+                0,6,5,0,0,2,0,7,4,
+                0,3,0,0,0,5,0,4,0,
+                0,0,1,8,0,0,0,0,0,
+                0,0,8,2,0,0,0,6,0,
+            ],
+            _ => panic!("Unsupported block size. Only 3 and 4 is ok for now.")
         };
 
-        sudoku.build_possible_values_db();
+        // MANY SOLUTIONS
+        // #[rustfmt::skip]
+        // let field = vec![
+        //     0,0,0,0,0,0,0,0,9,
+        //     0,0,0,0,8,9,0,2,0,
+        //     0,0,0,0,2,0,4,0,0,
+        //     0,0,4,0,6,0,0,0,8,
+        //     0,0,0,5,0,0,0,0,0,
+        //     0,6,5,0,0,2,0,7,4,
+        //     0,3,0,0,0,5,0,4,0,
+        //     0,0,1,8,0,0,0,0,0,
+        //     0,0,8,2,0,0,0,6,0,
+        // ];
 
-        sudoku.build_skip_dbs();
+        // HARD
+        // #[rustfmt::skip]
+        // let field = vec![
+        //     8,4,0,0,6,0,5,0,1,
+        //     0,0,0,0,0,3,0,4,0,
+        //     0,0,6,9,0,0,0,0,7,
+        //     0,2,0,7,1,0,0,0,6,
+        //     0,0,0,6,3,0,0,0,0,
+        //     9,0,0,0,0,0,0,5,0,
+        //     0,0,0,0,4,0,0,6,0,
+        //     2,0,0,0,0,0,1,8,0,
+        //     0,0,5,0,0,0,3,0,0,
+        // ];
 
-        sudoku
+        // EASY
-    }
+        // #[rustfmt::skip]
+        // let field = vec![
+        //     5,9,0,6,1,3,0,0,0,
+        //     0,0,0,9,0,0,5,0,0,
+        //     8,0,3,0,5,7,6,4,0,
+        //     0,7,5,0,0,0,4,0,6,
+        //     0,6,0,7,4,0,2,0,8,
+        //     2,0,8,0,0,0,7,5,3,
+        //     0,0,0,5,6,1,0,7,0,
+        //     0,0,1,0,7,0,9,0,0,
+        //     7,3,6,0,2,0,0,0,0,
+        // ];
 
-    fn build_skip_dbs(&mut self) {
+        let mut fixed = Vec::with_capacity(SIZE * SIZE);
-        fn find_fixed_streak_forward(mut idx: usize, field: &[u8]) -> u8 {
+        field.iter().for_each(|e| {
-            let mut fixed_count = 1;
+            if *e == 0 {
-            idx += 1;
+                fixed.push(0);
+            } else {
+                fixed.push(1);
+            }
+        });
 
-            while idx < NUM_FIELDS && field[idx] > 0 {
+        // create bitsets
-                fixed_count += 1;
+        // rows
-                idx += 1;
+        let mut bit_rows = [Bitset::new(); SIZE];
+        for row_nr in 0..SIZE {
+            let mut row = [0; SIZE];
+            for count in 0..SIZE {
+                row[count] = field[xy_to_pos(count, row_nr, SIZE)];
             }
 
-            fixed_count
+            row.into_iter()
+                .filter(|val| *val != 0)
+                .for_each(|val| bit_rows[row_nr].set(val - 1));
         }
 
-        fn find_fixed_streak_backward(mut idx: usize, field: &[u8]) -> u8 {
+        // cols
-            let mut fixed_count = 1;
+        let mut bit_cols = [Bitset::new(); SIZE];
-            idx -= 1;
+        for col_nr in 0..SIZE {
-
+            let mut col = [0; SIZE];
-            while idx < NUM_FIELDS && field[idx] > 0 {
+            for count in 0..SIZE {
-                fixed_count += 1;
+                col[count] = field[xy_to_pos(col_nr, count, SIZE)];
-                idx -= 1;
             }
 
-            fixed_count
+            col.into_iter()
+                .filter(|val| *val != 0)
+                .for_each(|val| bit_cols[col_nr].set(val - 1));
         }
 
-        let fwd = &mut self.skip_forward;
+        // blocks
-        for (idx, nr) in self.field.iter().enumerate() {
+        let mut bit_blocks = [Bitset::new(); SIZE];
-            match nr {
+
-                0 => fwd[idx] = *nr,
+        for block_nr in 0..SIZE {
-                _ => fwd[idx] = find_fixed_streak_forward(idx, &self.field),
+            let block_start_x = block_nr * BLOCK_SIZE % SIZE;
+            let block_start_y = block_nr * BLOCK_SIZE / SIZE * BLOCK_SIZE;
+
+            let mut block = [0; SIZE];
+            for count in 0..SIZE {
+                let block_offset_x = count % BLOCK_SIZE;
+                let block_offset_y = count / BLOCK_SIZE;
+
+                let field_x = block_start_x + block_offset_x;
+                let field_y = block_start_y + block_offset_y;
+
+                //dbg!(
+                //block_nr,
+                //block_start_x,
+                //block_start_y,
+                //block_offset_x,
+                //block_offset_y,
+                //field_x,
+                //field_y,
+                //);
+
+                block[count] = field[xy_to_pos(field_x, field_y, SIZE)];
             }
+
+            block
+                .into_iter()
+                .filter(|x| *x != 0)
+                .for_each(|x| bit_blocks[block_nr].set(x - 1));
         }
 
-        let bwd = &mut self.skip_backward;
+        //dbg!(bit_rows);
-        for (idx, nr) in self.field.iter().enumerate().rev() {
+        //dbg!(bit_cols);
-            match nr {
+        //dbg!(bit_blocks);
-                0 => bwd[idx + 1] = *nr,
+
-                _ => bwd[idx + 1] = find_fixed_streak_backward(idx, &self.field),
+        SField {
-            }
+            field,
+            fixed,
+            size: SIZE,
+            pos: 0,
+            pos_last_placed: 0,
+            num_fields: SIZE * SIZE,
+            possible_values: vec![vec![]; SIZE * SIZE],
+            rows: bit_rows,
+            cols: bit_cols,
+            blocks: bit_blocks,
         }
     }
 
     fn build_possible_values_db(&mut self) {
-        for idx in 0..NUM_FIELDS {
+        for idx in 0..self.num_fields {
-            if self.field[idx] != 0 {
+            if self.fixed[idx] == 1 {
                 continue;
             }
             self.pos = idx;
             // try all values between 1 and =self.size and remember the good ones
-            let mut good_ones = Vec::with_capacity(SIZE);
+            let mut good_ones = Vec::with_capacity(self.size);
-            for nr in 1..=(u8::try_from(SIZE).expect("SIZE is too big")) {
+            for nr in 1..=self.size {
                 if self.ok(nr) {
                     good_ones.push(nr);
                 }
@@ -119,87 +254,208 @@ impl SField {
     }
 
     pub fn solve_backtracking(&mut self) -> bool {
+        let mut found_solution = false;
         let mut num_solutions = 0;
 
+        let mut loop_count = 0;
+        let mut last_loop_count = 0;
+        let mut now = Instant::now();
         loop {
-            if !self.put_valid_nr() {
+            //std::thread::sleep_ms(30);
-                self.clear_current_field();
+            //self.print_clear();
-                if !self.prev() {
+            //self.print();
-                    print_clear();
+            loop_count += 1;
-                    self.print();
+            if now.elapsed().as_millis() >= 1000 {
-                    println!("Number of solutions: {num_solutions}");
+                now = Instant::now();
-                    break;
+                self.print_clear();
+                self.print();
+                println!("{} loops/s", loop_count - last_loop_count);
+                last_loop_count = loop_count;
+            }
+            if self.is_end() {
+                found_solution = true;
+                num_solutions += 1;
+                //if num_solutions % 100 == 0 {
+                //self.print_clear();
+                //println!("Solutions: {}", num_solutions);
+                //self.print();
+                //}
+
+                if self.is_fixed() {
+                    continue;
                 }
+                self.clear_current_field();
+                self.prev();
+                self.goto_prev_free_field();
+            }
+
+            if self.is_fixed() {
+                self.next();
                 continue;
             }
 
-            if !self.next() {
+            if self.goto_next_free_field() {
-                num_solutions += 1;
+                if self.put_valid_nr() {
-                if num_solutions % 10_000 == 0 {
+                    self.next();
-                    print_clear();
+                    continue;
-                    self.print();
+                } else {
-                    println!("Number of solutions: {num_solutions}");
+                    //println!("put_valid_nr failed for pos {}", self.pos);
+                    //std::thread::sleep_ms(300);
+                    self.clear_current_field();
+                    if !self.prev() {
+                        println!("Number of solutions: {}", num_solutions);
+                        break;
+                    }
+                    if !self.goto_prev_free_field() {
+                        println!("Number of solutions: {}", num_solutions);
+                        break;
+                    }
                 }
-
-                self.clear_current_field();
-                self.prev();
             }
         }
 
-        num_solutions > 0
+        found_solution
     }
 
+    #[inline(always)]
+    fn print_gray(&self) {
+        print!("\x1b\x5b\x31\x3b\x33\x30\x6d");
+    }
+
+    #[inline(always)]
+    fn print_green(&self) {
+        print!("\x1b\x5b\x31\x3b\x33\x32\x6d");
+    }
+
+    #[inline(always)]
+    fn print_red(&self) {
+        print!("\x1b\x5b\x31\x3b\x33\x31\x6d");
+    }
+
+    #[inline(always)]
+    fn print_neutral(&self) {
+        print!("\x1b\x5b\x31\x3b\x30\x6d");
+    }
+
+    #[inline(always)]
+    fn print_clear(&self) {
+        print!("\x1b\x5b\x48\x1b\x5b\x32\x4a");
+    }
+
+    #[inline(always)]
     fn print(&self) {
-        for i in 0..NUM_FIELDS {
+        for i in 0..self.num_fields {
-            if i != 0 && i % SIZE == 0 {
+            if i != 0 && i % self.size == 0 {
                 println!();
             }
 
-            if i == self.pos {
+            if i == self.pos_last_placed {
-                print_green();
+                self.print_red();
+            } else if i == self.pos {
+                self.print_green();
             } else if self.get_field_at_pos(i) == 0 {
-                print_gray();
+                self.print_gray();
             }
 
             print!("{:2} ", self.get_field_at_pos(i));
 
-            if i == self.pos || self.get_field_at_pos(i) == 0 {
+            if i == self.pos || i == self.pos_last_placed || self.get_field_at_pos(i) == 0 {
-                print_neutral();
+                self.print_neutral();
             }
         }
         println!();
     }
 
+    #[inline(always)]
     fn clear_current_field(&mut self) {
         self.set(0);
     }
 
+    #[inline(always)]
+    fn goto_prev_free_field(&mut self) -> bool {
+        while {
+            if !self.is_fixed() {
+                return true;
+            }
+            self.prev()
+        } {}
+
+        false
+    }
+
+    #[inline(always)]
+    fn goto_next_free_field(&mut self) -> bool {
+        while {
+            if !self.is_fixed() {
+                return true;
+            }
+            self.next()
+        } {}
+
+        false
+    }
+
+    #[inline(always)]
+    fn _put_valid_nr(&mut self) -> bool {
+        let current_nr = self.get_field_at_pos(self.pos);
+
+        for nr in current_nr..self.size + 1 {
+            if self.ok(nr) {
+                self.set(nr);
+                return true;
+            }
+        }
+
+        false
+    }
+
+    #[inline(always)]
     fn put_valid_nr(&mut self) -> bool {
         let current_nr = self.get_field_at_pos(self.pos);
 
         // safety:
         //     self.possible_vals is initialized with self.size * self.size
         //     so self.pos can safely be used to index here
-        let possible_vals = &self.possible_values[self.pos];
+        let possible_vals = unsafe { self.possible_values.get_unchecked(self.pos) };
 
-        for nr in possible_vals {
+        for nr in possible_vals.iter() {
             if *nr <= current_nr {
                 continue;
             }
 
-            if self.ok(*nr) {
+            let nr = *nr;
-                self.set(*nr);
+            if self.ok(nr) {
+                self.set(nr);
                 return true;
             }
         }
         false
     }
 
-    fn ok(&self, nr: u8) -> bool {
+    #[inline(always)]
-        self.block_ok(nr) && self.row_ok(nr) && self.col_ok(nr)
+    fn is_end(&self) -> bool {
+        !self.field.contains(&0)
     }
 
-    fn get_field_at_pos(&self, pos: usize) -> u8 {
+    #[inline(always)]
+    fn ok(&self, nr: usize) -> bool {
+        //self.block_ok(nr) && self.row_ok(nr) && self.col_ok(nr)
+
+        let (x, y, block_nr) = pos_to_xy_blocknr(self.pos, self.size);
+
+        !self.rows[y].get(nr - 1) && !self.cols[x].get(nr - 1) && !self.blocks[block_nr].get(nr - 1)
+    }
+
+    #[inline(always)]
+    fn is_fixed(&self) -> bool {
+        // safety: self.pos can be used to index the field unchecked
+        //         since the only methods modifying self.pos are
+        //         `next()` and `prev()` and they do bounds checking
+        unsafe { *self.fixed.get_unchecked(self.pos) == 1 }
+    }
+
+    #[inline(always)]
+    fn get_field_at_pos(&self, pos: usize) -> usize {
         // safety:
         //     TODO
         //     would need to mathematically explain that the calculations in
@@ -207,84 +463,125 @@ impl SField {
         unsafe { *self.field.get_unchecked(pos) }
     }
 
-    fn set(&mut self, nr: u8) {
+    #[inline(always)]
-        self.field[self.pos] = nr;
+    fn set(&mut self, nr: usize) {
+        let old = unsafe { self.field.get_unchecked_mut(self.pos) };
+
+        // if another number > 0 was in that cell, we need to remove that number from our bitsets
+        if *old > 0 {
+            let (x, y, block_nr) = pos_to_xy_blocknr(self.pos, self.size);
+            self.rows[y].unset(*old - 1);
+            self.cols[x].unset(*old - 1);
+            self.blocks[block_nr].unset(*old - 1);
+        }
+
+        // add new nr to our bitsets if it is a meaningful (> 0) number
+        if nr > 0 {
+            let (x, y, block_nr) = pos_to_xy_blocknr(self.pos, self.size);
+            self.rows[y].set(nr - 1);
+            self.cols[x].set(nr - 1);
+            self.blocks[block_nr].set(nr - 1);
+        }
+
+        // write the new number into the field
+        *old = nr;
+
+        // remember the last placed position for debugging purposes
+        self.pos_last_placed = self.pos;
     }
 
-    fn get_row(&self, row: &mut [u8; SIZE]) {
+    /*
+    #[inline(always)]
+    fn get_row(&self, row: &mut [usize]) {
         for (idx, row_elem) in row.iter_mut().enumerate() {
-            *row_elem = self.get_field_at_pos((self.pos / SIZE) * SIZE + idx);
+            *row_elem = self.get_field_at_pos((self.pos / self.size) * self.size + idx);
         }
     }
 
-    fn get_col(&self, col: &mut [u8; SIZE]) {
+    #[inline(always)]
+    fn get_col(&self, col: &mut [usize]) {
         for (idx, col_elem) in col.iter_mut().enumerate() {
-            *col_elem = self.get_field_at_pos(idx * SIZE + self.pos % SIZE);
+            *col_elem = self.get_field_at_pos(idx * self.size + self.pos % self.size);
         }
     }
 
-    fn get_block(&self, block: &mut [u8; SIZE]) {
+    #[inline(always)]
-        let block_start_row = self.pos / SIZE / BLOCK_SIZE * BLOCK_SIZE;
+    fn get_block(&self, block: &mut [usize]) {
-        let block_start_col = self.pos % SIZE / BLOCK_SIZE * BLOCK_SIZE;
+        let block_start_row = self.pos / self.size / self.block_size * self.block_size;
+        let block_start_col = self.pos % self.size / self.block_size * self.block_size;
 
-        for r in 0..BLOCK_SIZE {
+        for r in 0..self.block_size {
-            for c in 0..BLOCK_SIZE {
+            for c in 0..self.block_size {
-                block[r * BLOCK_SIZE + c] =
+                block[r * self.block_size + c] =
-                    self.get_field_at_pos(SIZE * (block_start_row + r) + block_start_col + c);
+                    self.get_field_at_pos(self.size * (block_start_row + r) + block_start_col + c);
             }
         }
     }
 
-    fn block_ok(&self, nr: u8) -> bool {
+    #[inline(always)]
-        let mut block = [0; SIZE];
+    fn block_ok(&self, nr: usize) -> bool {
-        self.get_block(&mut block);
+        let mut block = [0; MAX_BLOCK_SIZE * MAX_BLOCK_SIZE];
+        self.get_block(&mut block[0..self.size]);
         !block.contains(&nr)
     }
 
-    fn row_ok(&self, nr: u8) -> bool {
+    #[inline(always)]
-        let mut row = [0; SIZE];
+    fn row_ok(&self, nr: usize) -> bool {
-        self.get_row(&mut row);
+        let mut row = [0; MAX_BLOCK_SIZE * MAX_BLOCK_SIZE];
+        self.get_row(&mut row[0..self.size]);
         !row.contains(&nr)
     }
 
-    fn col_ok(&self, nr: u8) -> bool {
+    #[inline(always)]
-        let mut col = [0; SIZE];
+    fn col_ok(&self, nr: usize) -> bool {
-        self.get_col(&mut col);
+        let mut col = [0; MAX_BLOCK_SIZE * MAX_BLOCK_SIZE];
+        self.get_col(&mut col[0..self.size]);
         !col.contains(&nr)
     }
+    */
 
+    #[inline(always)]
     fn next(&mut self) -> bool {
-        let new_pos = self.pos + 1 + self.skip_forward[self.pos + 1] as usize;
+        if self.pos == self.num_fields - 1 {
-
-        if new_pos >= NUM_FIELDS {
             return false;
         }
 
-        self.pos = new_pos;
+        //println!("next {} -> {}", self.pos, self.pos + 1);
+        self.pos += 1;
         true
     }
 
+    #[inline(always)]
     fn prev(&mut self) -> bool {
-        let new_pos = self.pos - 1 - self.skip_backward[self.pos] as usize;
+        if self.pos == 0 {
-
-        if new_pos >= NUM_FIELDS {
             return false;
         }
 
-        self.pos = new_pos;
+        self.pos -= 1;
         true
     }
 
+    #[inline(always)]
     fn solve(&mut self) {
         let now = Instant::now();
         if !self.solve_backtracking() {
             println!("there is no solution.");
         }
-        eprintln!("took {:.3}s", now.elapsed().as_secs_f64());
+        println!("took {:.3}s", now.elapsed().as_secs_f64());
     }
 }
 
-fn main() {
+fn run() -> Result<(), String> {
     let mut field = SField::new();
+
+    field.build_possible_values_db();
+
     field.solve();
+    Ok(())
+}
+
+fn main() {
+    if let Err(e) = run() {
+        println!("{}", e)
+    }
 }