std/jpeg: halve maximum scan count from 64 to 32
cjpeg defaults to using 1 (sequential) or 10 (progressive) scans. 32 is
still easily more than what's seen in practice.
The previous commit (f9c384d6 std/jpeg: add "expect multiple scans"
check) makes Wuffs more closely match libjpeg. Without that commit,
though, this commit halves the time taken to decode the oss-fuzz test
case (linked below) from 6 to 3 seconds, in an optimized build. For the
debug-sanitizer fuzzer build, without this commit, that test case times
out after 60 seconds but this commit should halve the time taken.
Updates https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=70340
diff --git a/release/c/wuffs-unsupported-snapshot.c b/release/c/wuffs-unsupported-snapshot.c
index 89c73f1..f40fa2c 100644
--- a/release/c/wuffs-unsupported-snapshot.c
+++ b/release/c/wuffs-unsupported-snapshot.c
@@ -47714,7 +47714,7 @@
switch (coro_susp_point) {
WUFFS_BASE__COROUTINE_SUSPENSION_POINT_0;
- if (self->private_impl.f_scan_count >= 64u) {
+ if (self->private_impl.f_scan_count >= 32u) {
status = wuffs_base__make_status(wuffs_jpeg__error__unsupported_scan_count);
goto exit;
} else if ((self->private_impl.f_scan_count > 0u) && ! self->private_impl.f_expect_multiple_scans) {
diff --git a/std/jpeg/decode_jpeg.wuffs b/std/jpeg/decode_jpeg.wuffs
index f0deae2..d6fa4ec 100644
--- a/std/jpeg/decode_jpeg.wuffs
+++ b/std/jpeg/decode_jpeg.wuffs
@@ -1257,7 +1257,7 @@
var decode_mcu_result : base.u32
var bitstream_length : base.u32
- if this.scan_count >= 64 {
+ if this.scan_count >= 32 {
return "#unsupported scan count"
} else if (this.scan_count > 0) and (not this.expect_multiple_scans) {
return "#bad scan count"
