changed dynamic fse threshold for offset

recent experienced showed that
default distribution table for offset
can get it wrong pretty quickly with the nb of symbols,
while it remains a reasonable choice much longer for lengths symbols.

Changed the formula,
so that dynamic threshold is now 32 symbols for offsets.
It remains at 64 symbols for lengths.

Detection based on defaultNormLog

diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index df7cb8aa730ea1cd2e32d546ccc2ce61ad9fd6a4..e6b363ae0fba369a9617a8b4024068019581ec02 100644 (file)
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -1743,8 +1743,6 @@ ZSTD_selectEncodingType(
         ZSTD_defaultPolicy_e const isDefaultAllowed,
         ZSTD_strategy const strategy)
 {
-#define MIN_SEQ_FOR_DYNAMIC_FSE   64
-#define MAX_SEQ_FOR_STATIC_FSE  1000
     ZSTD_STATIC_ASSERT(ZSTD_defaultDisallowed == 0 && ZSTD_defaultAllowed != 0);
     if (mostFrequent == nbSeq) {
         *repeatMode = FSE_repeat_none;
@@ -1761,11 +1759,14 @@ ZSTD_selectEncodingType(
     }
     if (strategy < ZSTD_lazy) {
         if (isDefaultAllowed) {
-            if ((*repeatMode == FSE_repeat_valid) && (nbSeq < MAX_SEQ_FOR_STATIC_FSE)) {
+            size_t const staticFse_nbSeq_max = 1000;
+            size_t const dynamicFse_nbSeq_min = 1 << defaultNormLog;  /* 32 for offset, 64 for lengths */
+            assert(defaultNormLog >= 5 && defaultNormLog <= 6);  /* xx_DEFAULTNORMLOG */
+            if ((*repeatMode == FSE_repeat_valid) && (nbSeq < staticFse_nbSeq_max)) {
                 DEBUGLOG(5, "Selected set_repeat");
                 return set_repeat;
             }
-            if ((nbSeq < MIN_SEQ_FOR_DYNAMIC_FSE) || (mostFrequent < (nbSeq >> (defaultNormLog-1)))) {
+            if ((nbSeq < dynamicFse_nbSeq_min) || (mostFrequent < (nbSeq >> (defaultNormLog-1)))) {
                 DEBUGLOG(5, "Selected set_basic");
                 /* The format allows default tables to be repeated, but it isn't useful.
                  * When using simple heuristics to select encoding type, we don't want