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AAC: IEEE-754 type punning for 16-bit floating point rounding. 

Originally committed as revision 18015 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Alex Converse 2009-03-16 16:11:27 +00:00
parent 508fe07ab3
commit 4a39ccb403
1 changed files with 14 additions and 12 deletions
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26
libavcodec/aac.c
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@ -93,6 +93,8 @@
#include <math.h> #include <math.h>
#include <string.h> #include <string.h>
union float754 { float f; uint32_t i; };
static VLC vlc_scalefactors; static VLC vlc_scalefactors;
static VLC vlc_spectral[11]; static VLC vlc_spectral[11];
@ -930,24 +932,24 @@ static int decode_spectrum_and_dequant(AACContext * ac, float coef[1024], GetBit
} }
static av_always_inline float flt16_round(float pf) { static av_always_inline float flt16_round(float pf) {
int exp; union float754 tmp;
pf = frexpf(pf, &exp); tmp.f = pf;
pf = ldexpf(roundf(ldexpf(pf, 8)), exp-8); tmp.i = (tmp.i + 0x00008000U) & 0xFFFF0000U;
return pf; return tmp.f;
} }
static av_always_inline float flt16_even(float pf) { static av_always_inline float flt16_even(float pf) {
int exp; union float754 tmp;
pf = frexpf(pf, &exp); tmp.f = pf;
pf = ldexpf(rintf(ldexpf(pf, 8)), exp-8); tmp.i = (tmp.i + 0x00007FFFU + (tmp.i & 0x00010000U>>16)) & 0xFFFF0000U;
return pf; return tmp.f;
} }
static av_always_inline float flt16_trunc(float pf) { static av_always_inline float flt16_trunc(float pf) {
int exp; union float754 pun;
pf = frexpf(pf, &exp); pun.f = pf;
pf = ldexpf(truncf(ldexpf(pf, 8)), exp-8); pun.i &= 0xFFFF0000U;
return pf; return pun.f;
} }
static void predict(AACContext * ac, PredictorState * ps, float* coef, int output_enable) { static void predict(AACContext * ac, PredictorState * ps, float* coef, int output_enable) {