diff options
| author | Fabrice Bellard <fabrice@bellard.org> | 2002-10-03 21:03:59 +0000 |
|---|---|---|
| committer | Fabrice Bellard <fabrice@bellard.org> | 2002-10-03 21:03:59 +0000 |
| commit | 652f01978626257e38d1e333af45055d2b9465b5 (patch) | |
| tree | dd09bd5b0a1f5bb5225a3d26af77cb1ad29e3e92 /libavcodec/simple_idct.c | |
| parent | 5917d17cb79af27681209a745492bdccc37d2f76 (diff) | |
in fact IDCT248 needs to be normalized as I suspected
Originally committed as revision 997 to svn://svn.ffmpeg.org/ffmpeg/trunk
Diffstat (limited to 'libavcodec/simple_idct.c')
| -rw-r--r-- | libavcodec/simple_idct.c | 16 |
1 files changed, 7 insertions, 9 deletions
diff --git a/libavcodec/simple_idct.c b/libavcodec/simple_idct.c index 81e7af7809..ffb79f6db3 100644 --- a/libavcodec/simple_idct.c +++ b/libavcodec/simple_idct.c @@ -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]; |