[HUF] Improve Huffman encoding speed

Improve Huffman encoding speed by 20% for gcc and 10% for clang.

| Compiler |     Benchmark     | Config  |   Dataset   | Ratio | Speed MB/s (dev) | Speed MB/s (huf-cspeed) | Speed MB/s (huf-cspeed - dev) |
|----------|-------------------|---------|-------------|-------|------------------|-------------------------|-------------------------------|
| gcc      | compress          | level_1 | enwik7      | 2.43  | 253.70           | 258.72                  | 2.0%                          |
| gcc      | compress          | level_1 | silesia     | 2.88  | 341.90           | 348.15                  | 1.8%                          |
| gcc      | compress_literals | level_1 | enwik7      | 1.49  | 761.83           | 912.76                  | 19.8%                         |
| gcc      | compress_literals | level_1 | silesia     | 1.28  | 754.83           | 902.37                  | 19.5%                         |
| gcc      | compress_literals | level_7 | enwik7      | 1.29  | 502.81           | 552.79                  | 9.9%                          |
| gcc      | compress_literals | level_7 | silesia     | 1.11  | 675.97           | 776.44                  | 14.9%                         |
| clang    | compress          | level_1 | enwik7      | 2.43  | 277.54           | 280.98                  | 1.2%                          |
| clang    | compress          | level_1 | silesia     | 2.88  | 369.98           | 375.46                  | 1.5%                          |
| clang    | compress_literals | level_1 | enwik7      | 1.49  | 828.83           | 918.41                  | 10.8%                         |
| clang    | compress_literals | level_1 | silesia     | 1.28  | 815.81           | 905.41                  | 11.0%                         |
| clang    | compress_literals | level_7 | enwik7      | 1.29  | 533.13           | 553.30                  | 3.8%                          |
| clang    | compress_literals | level_7 | silesia     | 1.11  | 714.52           | 775.38                  | 8.5%                          |

lib/common/huf.h

@@ -89,9 +89,9 @@ HUF_PUBLIC_API size_t HUF_compress2 (void* dst, size_t dstCapacity,
 
 /** HUF_compress4X_wksp() :
  *  Same as HUF_compress2(), but uses externally allocated `workSpace`.
- * `workspace` must have minimum alignment of 4, and be at least as large as HUF_WORKSPACE_SIZE */
-#define HUF_WORKSPACE_SIZE ((6 << 10) + 256)
-#define HUF_WORKSPACE_SIZE_U32 (HUF_WORKSPACE_SIZE / sizeof(U32))
+ * `workspace` must be at least as large as HUF_WORKSPACE_SIZE */
+#define HUF_WORKSPACE_SIZE ((8 << 10) + 256)
+#define HUF_WORKSPACE_SIZE_U64 (HUF_WORKSPACE_SIZE / sizeof(U64))
 HUF_PUBLIC_API size_t HUF_compress4X_wksp (void* dst, size_t dstCapacity,
                                      const void* src, size_t srcSize,
                                      unsigned maxSymbolValue, unsigned tableLog,
@@ -136,15 +136,11 @@ HUF_PUBLIC_API size_t HUF_compress4X_wksp (void* dst, size_t dstCapacity,
 
 /* static allocation of HUF's Compression Table */
 /* this is a private definition, just exposed for allocation and strict aliasing purpose. never EVER access its members directly */
-struct HUF_CElt_s {
-  U16  val;
-  BYTE nbBits;
-};   /* typedef'd to HUF_CElt */
-typedef struct HUF_CElt_s HUF_CElt;   /* consider it an incomplete type */
-#define HUF_CTABLE_SIZE_U32(maxSymbolValue)   ((maxSymbolValue)+1)   /* Use tables of U32, for proper alignment */
-#define HUF_CTABLE_SIZE(maxSymbolValue)       (HUF_CTABLE_SIZE_U32(maxSymbolValue) * sizeof(U32))
+typedef size_t HUF_CElt;   /* consider it an incomplete type */
+#define HUF_CTABLE_SIZE_ST(maxSymbolValue)   ((maxSymbolValue)+2)   /* Use tables of size_t, for proper alignment */
+#define HUF_CTABLE_SIZE(maxSymbolValue)       (HUF_CTABLE_SIZE_ST(maxSymbolValue) * sizeof(size_t))
 #define HUF_CREATE_STATIC_CTABLE(name, maxSymbolValue) \
-    HUF_CElt name[HUF_CTABLE_SIZE_U32(maxSymbolValue)] /* no final ; */
+    HUF_CElt name[HUF_CTABLE_SIZE_ST(maxSymbolValue)] /* no final ; */
 
 /* static allocation of HUF's DTable */
 typedef U32 HUF_DTable;
@@ -250,11 +246,10 @@ size_t HUF_readStats_wksp(BYTE* huffWeight, size_t hwSize,
  *  Loading a CTable saved with HUF_writeCTable() */
 size_t HUF_readCTable (HUF_CElt* CTable, unsigned* maxSymbolValuePtr, const void* src, size_t srcSize, unsigned *hasZeroWeights);
 
-/** HUF_getNbBits() :
+/** HUF_getNbBitsFromCTable() :
  *  Read nbBits from CTable symbolTable, for symbol `symbolValue` presumed <= HUF_SYMBOLVALUE_MAX
- *  Note 1 : is not inlined, as HUF_CElt definition is private
- *  Note 2 : const void* used, so that it can provide a statically allocated table as argument (which uses type U32) */
-U32 HUF_getNbBits(const void* symbolTable, U32 symbolValue);
+ *  Note 1 : is not inlined, as HUF_CElt definition is private */
+U32 HUF_getNbBitsFromCTable(const HUF_CElt* symbolTable, U32 symbolValue);
 
 /*
  * HUF_decompress() does the following:
@@ -306,7 +301,7 @@ size_t HUF_decompress4X2_usingDTable(void* dst, size_t maxDstSize, const void* c
 /* ====================== */
 
 size_t HUF_compress1X (void* dst, size_t dstSize, const void* src, size_t srcSize, unsigned maxSymbolValue, unsigned tableLog);
-size_t HUF_compress1X_wksp (void* dst, size_t dstSize, const void* src, size_t srcSize, unsigned maxSymbolValue, unsigned tableLog, void* workSpace, size_t wkspSize);  /**< `workSpace` must be a table of at least HUF_WORKSPACE_SIZE_U32 unsigned */
+size_t HUF_compress1X_wksp (void* dst, size_t dstSize, const void* src, size_t srcSize, unsigned maxSymbolValue, unsigned tableLog, void* workSpace, size_t wkspSize);  /**< `workSpace` must be a table of at least HUF_WORKSPACE_SIZE_U64 U64 */
 size_t HUF_compress1X_usingCTable(void* dst, size_t dstSize, const void* src, size_t srcSize, const HUF_CElt* CTable);
 /** HUF_compress1X_repeat() :
  *  Same as HUF_compress1X_wksp(), but considers using hufTable if *repeat != HUF_repeat_none.