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avcodec/h274: don't read from uninitialized array members

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This bug flew under the radar because, in practice, these values are
0-initialized for the first invocation. But for subsequent invocations
(with different h/v values), reading from the uninitialized parts of
`out` is undefined behavior.

Avoid this by simply adjusting the iteration range of the following
loops. Has the added benefit of being a minor speedup.

Signed-off-by: James Almer <jamrial@gmail.com>
This commit is contained in:
Niklas Haas 2021-09-12 15:14:31 +02:00 committed by James Almer
parent c4973e2148
commit 52c35d648c
1 changed files with 3 additions and 3 deletions
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6
libavcodec/h274.c
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@ -74,9 +74,9 @@ static void init_slice_c(int8_t out[64][64], uint8_t h, uint8_t v,
// 64x64 inverse integer transform
for (int y = 0; y < 64; y++) {
for (int x = 0; x < 64; x++) {
for (int x = 0; x <= freq_h; x++) {
int32_t sum = 0;
for (int p = 0; p < 64; p++)
for (int p = 0; p <= freq_v; p++)
sum += R64T[y][p] * out[x][p];
tmp[y][x] = (sum + 128) >> 8;
}
@ -85,7 +85,7 @@ static void init_slice_c(int8_t out[64][64], uint8_t h, uint8_t v,
for (int y = 0; y < 64; y++) {
for (int x = 0; x < 64; x++) {
int32_t sum = 0;
for (int p = 0; p < 64; p++)
for (int p = 0; p <= freq_h; p++)
sum += tmp[y][p] * R64T[x][p]; // R64T^T = R64
// Renormalize and clip to [-127, 127]
out[y][x] = av_clip((sum + 128) >> 8, -127, 127);