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Don't allow default tables to repeat

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It isn't useful in any case to repeat default tables.
Saves a few bytes on Silesia, since we don't trigger the dictionary
heuristic.

Before: 211988480 => 73651998 bytes
After:  211988480 => 73651721 bytes
This commit is contained in:
Nick Terrell 2017-10-13 13:23:57 -07:00
parent b7977e348d
commit 7f961ba6cd
1 changed files with 7 additions and 1 deletions
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8
lib/compress/zstd_compress.c
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@ -1298,7 +1298,13 @@ symbolEncodingType_e ZSTD_selectEncodingType(
if ( isDefaultAllowed
&& ((nbSeq < MIN_SEQ_FOR_DYNAMIC_FSE) || (mostFrequent < (nbSeq >> (defaultNormLog-1)))) ) {
DEBUGLOG(5, "Selected set_basic");
*repeatMode = FSE_repeat_valid;
/* 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
* to confuse these tables with dictionaries. When running more careful
* analysis, we don't need to waste time checking both repeating tables
* and default tables.
*/
*repeatMode = FSE_repeat_none;
return set_basic;
}
DEBUGLOG(5, "Selected set_compressed");