| Message ID | 20190221193429.19600-2-michael@niedermayer.cc |
|---|---|
| State | Accepted |
| Commit | 3f68948cb3036e239baa17d88b2f2ef1ecbb8f0c |
| Headers | show |
On Thu, 21 Feb 2019 20:34:29 +0100 Michael Niedermayer <michael@niedermayer.cc> wrote: > Improves speed from 5.4 to 4.2 seconds > Fixes: 13149/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PGM_fuzzer-5760833622114304 LGTM Though, I really would expect the compiler to detect and optimize that. I wonder if "PNMContext * const sc" would help it any. - Lauri
On Fri, Feb 22, 2019 at 09:10:55AM +0200, Lauri Kasanen wrote: > On Thu, 21 Feb 2019 20:34:29 +0100 > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > Improves speed from 5.4 to 4.2 seconds > > Fixes: 13149/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PGM_fuzzer-5760833622114304 > > LGTM will apply > > Though, I really would expect the compiler to detect and optimize that. > I wonder if "PNMContext * const sc" would help it any. i doubt that would help. the char * pointer both the one we are reding from and the one we write to could in principle alias anything else (this is allowed in C) So the compiler would have to proof every time it writes to str/s that this cannot alias anything in the structure. And every time it writes to the structure that it cannot alias the bytestream its reading from. Otherwise it cannot optimize the operations out thanks [...]
diff --git a/libavcodec/pnm.c b/libavcodec/pnm.c index b06a6e81b5..17926f256f 100644 --- a/libavcodec/pnm.c +++ b/libavcodec/pnm.c @@ -36,13 +36,15 @@ static void pnm_get(PNMContext *sc, char *str, int buf_size) { char *s; int c; + uint8_t *bs = sc->bytestream; + const uint8_t *end = sc->bytestream_end; /* skip spaces and comments */ - while (sc->bytestream < sc->bytestream_end) { - c = *sc->bytestream++; + while (bs < end) { + c = *bs++; if (c == '#') { - while (c != '\n' && sc->bytestream < sc->bytestream_end) { - c = *sc->bytestream++; + while (c != '\n' && bs < end) { + c = *bs++; } } else if (!pnm_space(c)) { break; @@ -50,12 +52,13 @@ static void pnm_get(PNMContext *sc, char *str, int buf_size) } s = str; - while (sc->bytestream < sc->bytestream_end && !pnm_space(c)) { + while (bs < end && !pnm_space(c)) { if ((s - str) < buf_size - 1) *s++ = c; - c = *sc->bytestream++; + c = *bs++; } *s = '\0'; + sc->bytestream = bs; } int ff_pnm_decode_header(AVCodecContext *avctx, PNMContext * const s)
Improves speed from 5.4 to 4.2 seconds Fixes: 13149/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PGM_fuzzer-5760833622114304 Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> --- libavcodec/pnm.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)