From 4a39ccb40350a25719b1a43d2bacbd74fbd4f703 Mon Sep 17 00:00:00 2001 From: Alex Converse Date: Mon, 16 Mar 2009 16:11:27 +0000 Subject: [PATCH] AAC: IEEE-754 type punning for 16-bit floating point rounding. Originally committed as revision 18015 to svn://svn.ffmpeg.org/ffmpeg/trunk --- libavcodec/aac.c | 26 ++++++++++++++------------ 1 file changed, 14 insertions(+), 12 deletions(-) diff --git a/libavcodec/aac.c b/libavcodec/aac.c index 9a3b3d7ba8..9b230a5c5d 100644 --- a/libavcodec/aac.c +++ b/libavcodec/aac.c @@ -93,6 +93,8 @@ #include #include +union float754 { float f; uint32_t i; }; + static VLC vlc_scalefactors; 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) { - int exp; - pf = frexpf(pf, &exp); - pf = ldexpf(roundf(ldexpf(pf, 8)), exp-8); - return pf; + union float754 tmp; + tmp.f = pf; + tmp.i = (tmp.i + 0x00008000U) & 0xFFFF0000U; + return tmp.f; } static av_always_inline float flt16_even(float pf) { - int exp; - pf = frexpf(pf, &exp); - pf = ldexpf(rintf(ldexpf(pf, 8)), exp-8); - return pf; + union float754 tmp; + tmp.f = pf; + tmp.i = (tmp.i + 0x00007FFFU + (tmp.i & 0x00010000U>>16)) & 0xFFFF0000U; + return tmp.f; } static av_always_inline float flt16_trunc(float pf) { - int exp; - pf = frexpf(pf, &exp); - pf = ldexpf(truncf(ldexpf(pf, 8)), exp-8); - return pf; + union float754 pun; + pun.f = pf; + pun.i &= 0xFFFF0000U; + return pun.f; } static void predict(AACContext * ac, PredictorState * ps, float* coef, int output_enable) {