refactor HUF_compress_internal for clarity

changed workspace parameter convention
to always provide workspaceSize,
so that size can be explicitly checked.

Also, use more enum to make the meaning of some parameters more explicit.

lib/compress/hist.h

@@ -41,11 +41,11 @@
 
 /*! HIST_count():
  *  Provides the precise count of each byte within a table 'count'.
- *  'count' is a table of unsigned int, of minimum size (*maxSymbolValuePtr+1).
+ * 'count' is a table of unsigned int, of minimum size (*maxSymbolValuePtr+1).
  *  Updates *maxSymbolValuePtr with actual largest symbol value detected.
- *  @return : count of the most frequent symbol (which isn't identified).
- *            or an error code, which can be tested using HIST_isError().
- *            note : if return == srcSize, there is only one symbol.
+ * @return : count of the most frequent symbol (which isn't identified).
+ *           or an error code, which can be tested using HIST_isError().
+ *           note : if return == srcSize, there is only one symbol.
  */
 size_t HIST_count(unsigned* count, unsigned* maxSymbolValuePtr,
                   const void* src, size_t srcSize);
@@ -56,14 +56,16 @@ unsigned HIST_isError(size_t code);  /**< tells if a return value is an error co
 /* --- advanced histogram functions --- */
 
 #define HIST_WKSP_SIZE_U32 1024
+#define HIST_WKSP_SIZE    (HIST_WKSP_SIZE_U32 * sizeof(unsigned))
 /** HIST_count_wksp() :
  *  Same as HIST_count(), but using an externally provided scratch buffer.
  *  Benefit is this function will use very little stack space.
- * `workSpace` must be a table of unsigned of size >= HIST_WKSP_SIZE_U32
+ * `workSpace` is a writable buffer which must be 4-bytes aligned,
+ * `workSpaceSize` must be >= HIST_WKSP_SIZE
  */
 size_t HIST_count_wksp(unsigned* count, unsigned* maxSymbolValuePtr,
                        const void* src, size_t srcSize,
-                       unsigned* workSpace);
+                       void* workSpace, size_t workSpaceSize);
 
 /** HIST_countFast() :
  *  same as HIST_count(), but blindly trusts that all byte values within src are <= *maxSymbolValuePtr.
@@ -74,11 +76,12 @@ size_t HIST_countFast(unsigned* count, unsigned* maxSymbolValuePtr,
 
 /** HIST_countFast_wksp() :
  *  Same as HIST_countFast(), but using an externally provided scratch buffer.
- * `workSpace` must be a table of unsigned of size >= HIST_WKSP_SIZE_U32
+ * `workSpace` is a writable buffer which must be 4-bytes aligned,
+ * `workSpaceSize` must be >= HIST_WKSP_SIZE
  */
 size_t HIST_countFast_wksp(unsigned* count, unsigned* maxSymbolValuePtr,
                            const void* src, size_t srcSize,
-                           unsigned* workSpace);
+                           void* workSpace, size_t workSpaceSize);
 
 /*! HIST_count_simple() :
  *  Same as HIST_countFast(), this function is unsafe,