feat(compress): move dedicated dict param reversion to Rust

Port ZSTD_dedicatedDictSearch_revertCParams to a Rust leaf that accepts and
returns the complete repr(C) compression-parameter struct. Keep the existing
C pointer wrapper and call order before ZSTD_adjustCParams_internal, while
changing only hashLog for greedy, lazy, and lazy2 strategies.

Test Plan:
- cargo test --manifest-path rust/Cargo.toml --no-default-features --features compression
- cargo clippy --manifest-path rust/Cargo.toml --no-default-features --features compression (and --benches/--tests, rerun after fmt)
- cargo +nightly fmt --manifest-path rust/Cargo.toml
- make -B -C lib -j2 lib
- make -B -C tests -j2 fuzzer
- tests/fuzzer -s4560 -t47 -i48 -v
- tests/fuzzer -s4560 -t57 -i1057 -v
- make -B -C tests -j2 test-zstream
- git diff --check

lib/compress/zstd_compress.c

@@ -132,7 +132,8 @@ int ZSTD_rust_params_resolveExternalRepcodeSearch(int mode, int cLevel);
 int ZSTD_rust_params_cdictIndicesAreTagged(ZSTD_compressionParameters cParams);
 int ZSTD_rust_params_dedicatedDictSearchIsSupported(ZSTD_compressionParameters cParams);
 U32 ZSTD_rust_params_dedicatedDictSearch_getHashLog(U32 hashLog);
-U32 ZSTD_rust_params_dedicatedDictSearch_revertHashLog(U32 hashLog);
+ZSTD_compressionParameters
+ZSTD_rust_params_dedicatedDictSearch_revertCParams(ZSTD_compressionParameters cParams);
 int ZSTD_rust_params_shouldAttachDict(int strategy, int dedicatedDictSearch,
                                       U64 pledgedSrcSize, int attachDictPref,
                                       int forceWindow);
@@ -5678,21 +5679,7 @@ static ZSTD_compressionParameters ZSTD_dedicatedDictSearch_getCParams(int const
  */
 static void ZSTD_dedicatedDictSearch_revertCParams(
         ZSTD_compressionParameters* cParams) {
-    switch (cParams->strategy) {
+    *cParams = ZSTD_rust_params_dedicatedDictSearch_revertCParams(*cParams);
-        case ZSTD_fast:
-        case ZSTD_dfast:
-            break;
-        case ZSTD_greedy:
-        case ZSTD_lazy:
-        case ZSTD_lazy2:
-            cParams->hashLog = ZSTD_rust_params_dedicatedDictSearch_revertHashLog(cParams->hashLog);
-            break;
-        case ZSTD_btlazy2:
-        case ZSTD_btopt:
-        case ZSTD_btultra:
-        case ZSTD_btultra2:
-            break;
-    }
 }
 
 /*! ZSTD_getCParams_internal() :

rust/src/zstd_compress_params.rs

@@ -455,6 +455,19 @@ fn dedicated_dict_search_revert_hash_log(hash_log: u32) -> u32 {
         .max(ZSTD_HASHLOG_MIN as u32)
 }
 
+#[inline]
+fn dedicated_dict_search_revert_cparams(
+    mut cparams: ZSTD_compressionParameters,
+) -> ZSTD_compressionParameters {
+    match cparams.strategy {
+        ZSTD_GREEDY | ZSTD_LAZY | ZSTD_LAZY2 => {
+            cparams.hashLog = dedicated_dict_search_revert_hash_log(cparams.hashLog);
+        }
+        _ => {}
+    }
+    cparams
+}
+
 const ATTACH_DICT_SIZE_CUTOFFS: [u64; 10] = [
     8 * 1024,  /* unused */
     8 * 1024,  /* ZSTD_fast */
@@ -531,10 +544,12 @@ pub extern "C" fn ZSTD_rust_params_dedicatedDictSearch_getHashLog(hash_log: u32)
     dedicated_dict_search_get_hash_log(hash_log)
 }
 
-/// C ABI for the hash-log adjustment used by `ZSTD_dedicatedDictSearch_revertCParams()`.
+/// C ABI for `ZSTD_dedicatedDictSearch_revertCParams()`.
 #[no_mangle]
-pub extern "C" fn ZSTD_rust_params_dedicatedDictSearch_revertHashLog(hash_log: u32) -> u32 {
+pub extern "C" fn ZSTD_rust_params_dedicatedDictSearch_revertCParams(
-    dedicated_dict_search_revert_hash_log(hash_log)
+    cparams: ZSTD_compressionParameters,
+) -> ZSTD_compressionParameters {
+    dedicated_dict_search_revert_cparams(cparams)
 }
 
 /// C ABI for `ZSTD_shouldAttachDict()`.
@@ -1403,7 +1418,7 @@ mod tests {
             assert_eq!(adjusted, if should_adjust { 14 } else { original });
 
             let reverted = if should_adjust {
-                ZSTD_rust_params_dedicatedDictSearch_revertHashLog(adjusted)
+                dedicated_dict_search_revert_hash_log(adjusted)
             } else {
                 adjusted
             };
@@ -1412,26 +1427,87 @@ mod tests {
 
         assert_eq!(ZSTD_rust_params_dedicatedDictSearch_getHashLog(u32::MAX), 1);
         assert_eq!(
-            ZSTD_rust_params_dedicatedDictSearch_revertHashLog(ZSTD_HASHLOG_MIN as u32),
+            dedicated_dict_search_revert_hash_log(ZSTD_HASHLOG_MIN as u32),
             ZSTD_HASHLOG_MIN as u32
         );
         assert_eq!(
-            ZSTD_rust_params_dedicatedDictSearch_revertHashLog(ZSTD_HASHLOG_MIN as u32 + 1),
+            dedicated_dict_search_revert_hash_log(ZSTD_HASHLOG_MIN as u32 + 1),
             ZSTD_HASHLOG_MIN as u32
         );
         assert_eq!(
-            ZSTD_rust_params_dedicatedDictSearch_revertHashLog(ZSTD_HASHLOG_MIN as u32 + 2),
+            dedicated_dict_search_revert_hash_log(ZSTD_HASHLOG_MIN as u32 + 2),
             ZSTD_HASHLOG_MIN as u32
         );
+        assert_eq!(dedicated_dict_search_revert_hash_log(0), u32::MAX - 1);
+        assert_eq!(dedicated_dict_search_revert_hash_log(1), u32::MAX);
+    }
+
+    #[test]
+    fn dedicated_dict_search_revert_cparams_preserves_fields_and_strategy_policy() {
+        let strategies = [
+            ZSTD_FAST,
+            ZSTD_DFAST,
+            ZSTD_GREEDY,
+            ZSTD_LAZY,
+            ZSTD_LAZY2,
+            ZSTD_BTLAZY2,
+            ZSTD_BTOPT,
+            ZSTD_BTULTRA,
+            ZSTD_BTULTRA2,
+            -1,
+            99,
+        ];
+
+        for strategy in strategies {
+            let input = ZSTD_compressionParameters {
+                windowLog: 21,
+                chainLog: 19,
+                hashLog: 12,
+                searchLog: 5,
+                minMatch: 4,
+                targetLength: 48,
+                strategy,
+            };
+            let output = dedicated_dict_search_revert_cparams(input);
+            let expected_hash_log = if matches!(strategy, ZSTD_GREEDY | ZSTD_LAZY | ZSTD_LAZY2) {
+                10
+            } else {
+                input.hashLog
+            };
+
+            assert_eq!(output.hashLog, expected_hash_log, "strategy {strategy}");
+            assert_eq!(output.windowLog, input.windowLog, "strategy {strategy}");
+            assert_eq!(output.chainLog, input.chainLog, "strategy {strategy}");
+            assert_eq!(output.searchLog, input.searchLog, "strategy {strategy}");
+            assert_eq!(output.minMatch, input.minMatch, "strategy {strategy}");
             assert_eq!(
-            ZSTD_rust_params_dedicatedDictSearch_revertHashLog(0),
+                output.targetLength, input.targetLength,
+                "strategy {strategy}"
+            );
+            assert_eq!(output.strategy, input.strategy, "strategy {strategy}");
+        }
+
+        for strategy in [ZSTD_GREEDY, ZSTD_LAZY, ZSTD_LAZY2] {
+            let mut input = ZSTD_compressionParameters {
+                hashLog: ZSTD_HASHLOG_MIN as u32,
+                strategy,
+                ..ZSTD_compressionParameters::default()
+            };
+            assert_eq!(dedicated_dict_search_revert_cparams(input).hashLog, 6);
+
+            input.hashLog = 0;
+            assert_eq!(
+                dedicated_dict_search_revert_cparams(input).hashLog,
                 u32::MAX - 1
             );
+
+            input.hashLog = 1;
             assert_eq!(
-            ZSTD_rust_params_dedicatedDictSearch_revertHashLog(1),
+                dedicated_dict_search_revert_cparams(input).hashLog,
                 u32::MAX
             );
         }
+    }
 
     #[test]
     fn dictionary_attachment_matches_strategy_size_and_preference_boundaries() {