Adding shrinking flag for cover and fastcover (#1656)

* Changed ERROR(GENERIC) excluding inits

* editing git ignore

* Edited init functions to size_t returns

* moved declarations earlier

* resolved issues with changes to init functions

* fixed style and an error check

* attempting to add tests that might trigger changes

* added && die to cases expecting to fail

* resolved no die on expected failed command

* fixed accel to be incorrect value

* Adding an automated shrinking option

* Fixing build

* finalizing fixes

* fix?

* Removing added comment in cover.h

* Styling fixes

* Merging with fb dev

* removing megic number for default regression

* Requested revisions

* fixing support for fast cover

* fixing casting errors

* parenthesis fix

* fixing some build nits

* resolving travis ci syntax

* might resolve all compilation issues

* removed unused variable

* remodeling the selectDict function

* fixing bad memory access

* fixing error checks

* fixed erroring check in selectDict

* fixing mixed declarations

* modify mixed declaration

* fixing nits and adding test cases

* Adding requested changes + fixed bug for error checking

* switched double comparison from != to <

* fixed declaration typing

* refactoring COVER_best_finish() and changing shrinkDict

* removing the const's

* modifying ZDICT_optimizeTrainFromBuffer_cover functions

* fixing potential bad memcpy

* fixing the error function for dict size

lib/dictBuilder/cover.h

@@ -46,6 +46,15 @@ typedef struct {
   U32 size;
 } COVER_epoch_info_t;
 
+/**
+ * Struct used for the dictionary selection function.
+ */
+typedef struct COVER_dictSelection {
+  BYTE* dictContent;
+  size_t dictSize;
+  size_t totalCompressedSize;
+} COVER_dictSelection_t;
+
 /**
  * Computes the number of epochs and the size of each epoch.
  * We will make sure that each epoch gets at least 10 * k bytes.
@@ -107,6 +116,32 @@ void COVER_best_start(COVER_best_t *best);
  * Decrements liveJobs and signals any waiting threads if liveJobs == 0.
  * If this dictionary is the best so far save it and its parameters.
  */
-void COVER_best_finish(COVER_best_t *best, size_t compressedSize,
-                       ZDICT_cover_params_t parameters, void *dict,
-                       size_t dictSize);
+void COVER_best_finish(COVER_best_t *best, ZDICT_cover_params_t parameters,
+                       COVER_dictSelection_t selection);
+/**
+ * Error function for COVER_selectDict function. Checks if the return
+ * value is an error.
+ */
+unsigned COVER_dictSelectionIsError(COVER_dictSelection_t selection);
+
+ /**
+  * Error function for COVER_selectDict function. Returns a struct where
+  * return.totalCompressedSize is a ZSTD error.
+  */
+COVER_dictSelection_t COVER_dictSelectionError(size_t error);
+
+/**
+ * Always call after selectDict is called to free up used memory from
+ * newly created dictionary.
+ */
+void COVER_dictSelectionFree(COVER_dictSelection_t selection);
+
+/**
+ * Called to finalize the dictionary and select one based on whether or not
+ * the shrink-dict flag was enabled. If enabled the dictionary used is the
+ * smallest dictionary within a specified regression of the compressed size
+ * from the largest dictionary.
+ */
+ COVER_dictSelection_t COVER_selectDict(BYTE* customDictContent,
+                       size_t dictContentSize, const BYTE* samplesBuffer, const size_t* samplesSizes, unsigned nbFinalizeSamples,
+                       size_t nbCheckSamples, size_t nbSamples, ZDICT_cover_params_t params, size_t* offsets, size_t totalCompressedSize);