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in fact IDCT248 needs to be normalized as I suspected

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Originally committed as revision 997 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Fabrice Bellard 2002-10-03 21:03:59 +00:00
parent 5917d17cb7
commit 652f019786
2 changed files with 27 additions and 25 deletions
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36
libavcodec/dct-test.c
View File

@ -299,10 +299,11 @@ void idct248_ref(UINT8 *dest, int linesize, INT16 *block)
}
/* butterfly */
s = 0.5 * sqrt(2.0);
for(i=0;i<4;i++) {
for(j=0;j<8;j++) {
block1[8*(2*i)+j] = (block[8*(2*i)+j] + block[8*(2*i+1)+j]) * 0.5;
block1[8*(2*i+1)+j] = (block[8*(2*i)+j] - block[8*(2*i+1)+j]) * 0.5;
block1[8*(2*i)+j] = (block[8*(2*i)+j] + block[8*(2*i+1)+j]) * s;
block1[8*(2*i+1)+j] = (block[8*(2*i)+j] - block[8*(2*i+1)+j]) * s;
}
}
@ -336,7 +337,7 @@ void idct248_ref(UINT8 *dest, int linesize, INT16 *block)
/* clamp and store the result */
for(i=0;i<8;i++) {
for(j=0;j<8;j++) {
v = block3[8*i+j] + 128.0;
v = block3[8*i+j];
if (v < 0)
v = 0;
else if (v > 255)
@ -357,13 +358,27 @@ void idct248_error(const char *name,
important here) */
err_max = 0;
for(it=0;it<NB_ITS;it++) {
for(i=0;i<64;i++)
block1[i] = (random() % 512) - 256;
/* XXX: use forward transform to generate values */
for(i=0;i<64;i++)
block1[i] = (random() % 256) - 128;
block1[0] += 1024;
for(i=0; i<64; i++)
block[i]= block1[i];
idct248_ref(img_dest1, 8, block);
for(i=0; i<64; i++)
block[i]= block1[i];
idct248_put(img_dest, 8, block);
for(i=0;i<64;i++) {
v = abs((int)img_dest[i] - (int)img_dest1[i]);
if (v == 255)
printf("%d %d\n", img_dest[i], img_dest1[i]);
if (v > err_max)
err_max = v;
}
#if 0
printf("ref=\n");
for(i=0;i<8;i++) {
@ -373,13 +388,7 @@ void idct248_error(const char *name,
}
printf("\n");
}
#endif
for(i=0; i<64; i++)
block[i]= block1[i];
idct248_put(img_dest, 8, block);
#if 0
printf("out=\n");
for(i=0;i<8;i++) {
int j;
@ -389,11 +398,6 @@ void idct248_error(const char *name,
printf("\n");
}
#endif
for(i=0;i<64;i++) {
v = abs(img_dest[i] - img_dest1[i]);
if (v > err_max)
err_max = v;
}
}
printf("%s %s: err_inf=%d\n",
1 ? "IDCT248" : "DCT248",

16
libavcodec/simple_idct.c
View File

@ -663,14 +663,12 @@ void simple_idct(INT16 *block)
#define CN_SHIFT 12
#define C_FIX(x) ((int)((x) * (1 << CN_SHIFT) + 0.5))
#define C0 C_FIX(0.7071067811)
#define C1 C_FIX(0.9238795324)
#define C2 C_FIX(0.3826834324)
#define C1 C_FIX(0.6532814824)
#define C2 C_FIX(0.2705980501)
/* row idct is multiple by 16 * sqrt(2.0), col idct4 is multiplied by
sqrt(2). An extra division by two is needed for the first butterfly
stage */
#define C_SHIFT (4+1+12+1)
/* row idct is multiple by 16 * sqrt(2.0), col idct4 is normalized,
and the butterfly must be multiplied by 0.5 * sqrt(2.0) */
#define C_SHIFT (4+1+12)
static inline void idct4col(UINT8 *dest, int line_size, const INT16 *col)
{
@ -681,8 +679,8 @@ static inline void idct4col(UINT8 *dest, int line_size, const INT16 *col)
a1 = col[8*2];
a2 = col[8*4];
a3 = col[8*6];
c0 = (a0 + a2) * C0 + (1 << (C_SHIFT - 1)) + (128 << C_SHIFT);
c2 = (a0 - a2) * C0 + (1 << (C_SHIFT - 1)) + (128 << C_SHIFT);
c0 = ((a0 + a2) << (CN_SHIFT - 1)) + (1 << (C_SHIFT - 1));
c2 = ((a0 - a2) << (CN_SHIFT - 1)) + (1 << (C_SHIFT - 1));
c1 = a1 * C1 + a3 * C2;
c3 = a1 * C2 - a3 * C1;
dest[0] = cm[(c0 + c1) >> C_SHIFT];