From: Yoni Gilad <yonig@radcom.com>
Date: Thu, 17 Feb 2022 17:46:29 +0000 (+0200)
Subject: seekable_format: Prevent rereading frame when seeking forward
X-Git-Tag: v1.5.5~2^2~4^2~1
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=618bf84e0d16070ac67a80b404041adb264c4952;p=thirdparty%2Fzstd.git

seekable_format: Prevent rereading frame when seeking forward

When decompressing a seekable file, if seeking forward within
a frame (by issuing multiple ZSTD_seekable_decompress calls
with a small gap between them), the frame will be unnecessarily
reread from the beginning. This patch makes it continue using
the current frame data and simply skip over the unneeded bytes.
---

diff --git a/contrib/seekable_format/zstdseek_decompress.c b/contrib/seekable_format/zstdseek_decompress.c
index fbb2d4fe3..4fefc5f2e 100644
--- a/contrib/seekable_format/zstdseek_decompress.c
+++ b/contrib/seekable_format/zstdseek_decompress.c
@@ -493,7 +493,7 @@ size_t ZSTD_seekable_decompress(ZSTD_seekable* zs, void* dst, size_t len, unsign
     size_t srcBytesRead = 0;
     do {
         /* check if we can continue from a previous decompress job */
-        if (targetFrame != zs->curFrame || offset != zs->decompressedOffset) {
+        if (targetFrame != zs->curFrame || offset < zs->decompressedOffset) {
             zs->decompressedOffset = zs->seekTable.entries[targetFrame].dOffset;
             zs->curFrame = targetFrame;