Changed default level 18 (large input)

Previous -18 : 4.7 MB/s, R:3.833
New -18 : 5.1 MB/s. R:3.825

It's a better fit within -17 (6.8 MB/s) and -19 (4.0 MB/s)
The new level 18 also uses significantly less memory.
And, it makes a good transition between level 17 (mml5)
and level 19 (mml3).
Up to now, there was no level with mml4.

(note : minmatch setting can have a large impact on some (specific) datasets)

diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index 9a2d194ad79e9c3f1eeaea728bfe2879be8e8cbf..74ae66cb7426b9dfe20f2e57de9f8d3b5bea713c 100644 (file)
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -3432,7 +3432,7 @@ static const ZSTD_compressionParameters ZSTD_defaultCParameters[4][ZSTD_MAX_CLEV
     { 22, 21, 21,  5,  5, 16, ZSTD_btlazy2 },  /* level 15 */
     { 23, 22, 22,  5,  5, 16, ZSTD_btlazy2 },  /* level 16 */
     { 23, 21, 22,  4,  5, 24, ZSTD_btopt   },  /* level 17 */
-    { 23, 23, 22,  6,  5, 32, ZSTD_btopt   },  /* level 18 */
+    { 23, 22, 22,  5,  4, 32, ZSTD_btopt   },  /* level 18 */
     { 23, 23, 22,  6,  3, 48, ZSTD_btopt   },  /* level 19 */
     { 25, 25, 23,  7,  3, 64, ZSTD_btopt2  },  /* level 20 */
     { 26, 26, 23,  7,  3,256, ZSTD_btopt2  },  /* level 21 */