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swscale: fix overflow in 16-bit vertical scaling. 

We operated on 31-bits, but with e.g. lanczos scaling, values can
add up to beyond 0x80000000, thus leading to output of zeroes. Drop
one bit of precision fixes this.
This commit is contained in:
Ronald S. Bultje 2011-07-08 14:57:07 -07:00 committed by Michael Niedermayer
parent 71a04bc19d
commit 93a10dd561
1 changed files with 9 additions and 9 deletions
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18
libswscale/swscale.c
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@ -302,7 +302,7 @@ yuv2yuvX16_c_template(const int16_t *lumFilter, const int32_t **lumSrc,
int dword= output_bits == 16;
uint16_t *yDest = dest[0], *uDest = dest[1], *vDest = dest[2],
*aDest = CONFIG_SWSCALE_ALPHA ? dest[3] : NULL;
int shift = 11 + 4*dword + 16 - output_bits;
int shift = 11 + 4*dword + 16 - output_bits - 1;
#define output_pixel(pos, val) \
if (big_endian) { \
@ -319,24 +319,24 @@ yuv2yuvX16_c_template(const int16_t *lumFilter, const int32_t **lumSrc,
} \
}
for (i = 0; i < dstW; i++) {
int val = 1 << (26-output_bits + 4*dword);
int val = 1 << (26-output_bits + 4*dword - 1);
int j;
for (j = 0; j < lumFilterSize; j++)
val += (dword ? lumSrc[j][i] : ((int16_t**)lumSrc)[j][i]) * lumFilter[j];
val += ((dword ? lumSrc[j][i] : ((int16_t**)lumSrc)[j][i]) * lumFilter[j])>>1;
output_pixel(&yDest[i], val);
}
if (uDest) {
for (i = 0; i < chrDstW; i++) {
int u = 1 << (26-output_bits + 4*dword);
int v = 1 << (26-output_bits + 4*dword);
int u = 1 << (26-output_bits + 4*dword - 1);
int v = 1 << (26-output_bits + 4*dword - 1);
int j;
for (j = 0; j < chrFilterSize; j++) {
u += (dword ? chrUSrc[j][i] : ((int16_t**)chrUSrc)[j][i]) * chrFilter[j];
v += (dword ? chrVSrc[j][i] : ((int16_t**)chrVSrc)[j][i]) * chrFilter[j];
u += ((dword ? chrUSrc[j][i] : ((int16_t**)chrUSrc)[j][i]) * chrFilter[j]) >> 1;
v += ((dword ? chrVSrc[j][i] : ((int16_t**)chrVSrc)[j][i]) * chrFilter[j]) >> 1;
}
output_pixel(&uDest[i], u);
@ -346,11 +346,11 @@ yuv2yuvX16_c_template(const int16_t *lumFilter, const int32_t **lumSrc,
if (CONFIG_SWSCALE_ALPHA && aDest) {
for (i = 0; i < dstW; i++) {
int val = 1 << (26-output_bits + 4*dword);
int val = 1 << (26-output_bits + 4*dword - 1);
int j;
for (j = 0; j < lumFilterSize; j++)
val += (dword ? alpSrc[j][i] : ((int16_t**)alpSrc)[j][i]) * lumFilter[j];
val += ((dword ? alpSrc[j][i] : ((int16_t**)alpSrc)[j][i]) * lumFilter[j]) >> 1;
output_pixel(&aDest[i], val);
}