From: Yann Collet <cyan@fb.com>
Date: Mon, 26 Feb 2024 21:27:59 +0000 (-0800)
Subject: optimization: bail out faster in presence of incompressible data
X-Git-Tag: v1.5.6^2~60^2~2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=86db60752d1f813642054d12d704663c7757d434;p=thirdparty%2Fzstd.git

optimization: bail out faster in presence of incompressible data
---

diff --git a/lib/compress/zstd_compress_superblock.c b/lib/compress/zstd_compress_superblock.c
index e9038c472..a9e9493be 100644
--- a/lib/compress/zstd_compress_superblock.c
+++ b/lib/compress/zstd_compress_superblock.c
@@ -521,6 +521,9 @@ static size_t ZSTD_compressSubBlock_multi(const seqStore_t* seqStorePtr,
         DEBUGLOG(5, "estimated fullblock size=%u bytes ; avgLitCost=%.2f ; avgSeqCost=%.2f ; targetCBlockSize=%u, nbSubBlocks=%u ; avgBlockBudget=%.0f bytes",
                     (unsigned)ebs.estBlockSize, (double)avgLitCost/BYTESCALE, (double)avgSeqCost/BYTESCALE,
                     (unsigned)targetCBlockSize, (unsigned)nbSubBlocks, (double)avgBlockBudget/BYTESCALE);
+        /* simplification: if estimates states that the full superblock doesn't compress, just bail out immediately
+         * this will result in the production of a single uncompressed block covering @srcSize.*/
+        if (ebs.estBlockSize > srcSize) return 0;
 
         /* compress and write sub-blocks */
         for (n=0; n+1 < nbSubBlocks; n++) {
@@ -568,7 +571,7 @@ static size_t ZSTD_compressSubBlock_multi(const seqStore_t* seqStorePtr,
                     sp += seqCount;
                     blockBudgetSupp = 0;
             }   }
-            /* otherwise : do not compress yet, coalesce current block with next one */
+            /* otherwise : do not compress yet, coalesce current sub-block with following one */
         }
     } /* if (nbSeqs > 0) */