1 files changed, 50 insertions, 0 deletions
diff --git a/backport-Fix-a-bug-in-ZLIB_DEBUG-compiles-in-check_match.patch b/backport-Fix-a-bug-in-ZLIB_DEBUG-compiles-in-check_match.patch
new file mode 100644
index 0000000..18bc6a8
--- /dev/null
+++ b/backport-Fix-a-bug-in-ZLIB_DEBUG-compiles-in-check_match.patch
@@ -0,0 +1,50 @@
+From 7af6320ad78b390de42f414fabdc64dc6d67a5ea Mon Sep 17 00:00:00 2001
+From: Mark Adler <madler@alumni.caltech.edu>
+Date: Fri, 19 Jan 2024 12:19:53 -0800
+Subject: [PATCH] Fix a bug in ZLIB_DEBUG compiles in check_match().
+
+This avoids trying to compare a match starting one byte before the
+current window. Thanks to @zmodem (Hans) for discovering this.
+
+Reference:https://github.com/madler/zlib/commit/7af6320ad78b390de42f414fabdc64dc6d67a5ea
+Conflict: Patch context adaptation
+
+---
+ deflate.c | 20 ++++++++++++++------
+ 1 file changed, 14 insertions(+), 6 deletions(-)
+
+diff --git a/deflate.c b/deflate.c
+index 8088083..396ab12 100644
+--- a/deflate.c
++++ b/deflate.c
+@@ -1510,13 +1510,21 @@ local void check_match(s, start, match, length)
+     int length;
+ {
+     /* check that the match is indeed a match */
+-    if (zmemcmp(s->window + match,
+-                s->window + start, length) != EQUAL) {
+-        fprintf(stderr, " start %u, match %u, length %d\n",
+-                start, match, length);
++    Bytef *back = s->window + (int)match, *here = s->window + start;
++    IPos len = length;
++    if (match == (IPos)-1) {
++        /* match starts one byte before the current window -- just compare the
++           subsequent length-1 bytes */
++        back++;
++        here++;
++        len--;
++    }
++    if (zmemcmp(back, here, len) != EQUAL) {
++        fprintf(stderr, " start %u, match %d, length %d\n",
++                start, (int)match, length);
+         do {
+-            fprintf(stderr, "%c%c", s->window[match++], s->window[start++]);
+-        } while (--length != 0);
++            fprintf(stderr, "(%02x %02x)", *back++, *here++);
++        } while (--len != 0);
+         z_error("invalid match");
+     }
+     if (z_verbose > 1) {
+-- 
+2.33.0
+