#include?“mp3dec.h“

/*?An?Inverse?Modified?Discrete?Cosinus?Transform?is?applied?to?18?values
???at?a?time.?The?18?frequency?values?generate?36?time?domain?values?
???where?half?of?these?are?overlapped?with?half?of?the?previously?generated
???values?to?produce?18?output?values.?These?can?later?be?fed?into?the
???subband?synthesis.

???The?multiply-add?loop?here?is?very?time?critical.?It?uses?a?total?of
???684*32=21888?MAC?operations?per?imdct?4?times?per?frame.?With?38
???frames?per?second?thats?3.33?million?MAC‘s.

???Using?some?small?trigonometric?tricks?we?can?do?this?in?360*32*4*38=
???1.75?million?MAC‘s?per?second?instead.

*/

extern?mpfloat?Granule_imdct_previous[2][576];??/*?used?for?overlapping?*/
extern?mpfloat?Granule_9x9_idct[72];
extern?mpfloat?Granule_imdct_win[4][36];

mpfloat?Granule_twiddles_short[23]?=?{
????0.866025403f?0.5f
????1.931851653f?0.707106781f?0.517638090f

????0.504314480f?0.541196100f?0.630236207f
????0.821339815f?1.306562965f?3.830648788f
????0.793353340f?0.608761429f?0.923879532f
????0.382683432f?0.991444861f?0.130526192f?
????0.382683432f?0.608761429f?0.793353340f
????0.923879532f?0.991444861f?0.130526192f
};

mpfloat?Granule_twiddles_normal[]?=?{
????5.736856623f?1.931851653f?1.183100792f
????0.871723397f?0.707106781f?0.610387294f?
????0.551688959f?0.517638090f?0.501909918f

????-0.500476342f?-0.504314480f?-0.512139757f
????-0.524264562f?-0.541196100f?-0.563690973f?
????-0.592844523f?-0.630236207f?-0.678170852f?
????-0.740093616f?-0.821339815f?-0.930579498f
????-1.082840285f?-1.306562965f?-1.662754762f?
????-2.310113158f?-3.830648788f?-11.46279281f
};

void
Granule_imdct（Granule?*gr?int?ch?Granule_floatfreqs?X）
{
????int?sb?i?j?k?l?window;
????mpfloat?save?sum?sum2?pp1;
????mpfloat?s;
????mpfloat?x[36]?t[18];
????mpfloat?*v?*prev?*z?*twid;

????prev?=?Granule_imdct_previous[ch];

????/*?process?each?subband?*/

????for（sb?=?0;?sb?
	for（i?=?0;?i?	????x[i]?=?（mpfloat）0.0f;
	
	/*?decode?the?block_type?-?it‘s?in?block_type?but?we?have?to?think
	???about?the?mixed?blocks?lower?2?subbands?*/
	
	if（gr->block_type?==?BLOCKTYPE_3WIN?&&
	???!（gr->window_switching_flag?&&?
	?????gr->mixed_block_flag?&&?sb?
	????/*?process?the?3?windows?separately?each?window?has?12?values?*/

	????for（window?=?0;?window?
#ifdef?LEE_IMDCT
		/*?30*3=90?adds?25*3=75?muls?*/

		X[15+window]?+=?X[12+window];
		X[12+window]?+=?X[9+window];
		X[9+window]?+=?X[6+window];
		X[6+window]?+=?X[3+window];
		X[3+window]?+=?X[window];

		X[15+window]?+=?X[9+window];
		X[9+window]?+=?X[3+window];

		twid?=?Granule_twiddles_short;

		/*?do?a?3x3?IDCT?on?the?even?part?*/

		pp1?=?X[6+window]?*?twid[0];
		sum?=?X[window]?+?X[12+window]?*?twid[1];
		t[1]?=?X[window]?-?X[12+window];
		t[0]?=?sum?+?pp1;
		t[2]?=?sum?-?pp1;

		/*?3x3?IDCT

?屬性????????????大小?????日期????時間???名稱
-----------?---------??----------?-----??----

?????文件???????8953??1999-03-22?16:20??用DSP進行mp3解壓縮的算法原程序\fastimdct.c

?????文件???????5475??1999-03-22?16:20??用DSP進行mp3解壓縮的算法原程序\FASTSB.C

?????文件???????9515??1999-03-22?16:20??用DSP進行mp3解壓縮的算法原程序\HUFF.C

?????文件??????19029??1999-03-22?16:20??用DSP進行mp3解壓縮的算法原程序\HUFFMAN.H

?????文件??????56613??1999-03-22?16:20??用DSP進行mp3解壓縮的算法原程序\MP3DEC.C

?????文件??????12117??1999-03-22?16:20??用DSP進行mp3解壓縮的算法原程序\MP3DEC.H

?????文件???????6053??1999-03-22?16:20??用DSP進行mp3解壓縮的算法原程序\MP3DEC_D.H

?????文件???????1364??1999-03-22?16:20??用DSP進行mp3解壓縮的算法原程序\windowing.c

?????目錄??????????0??2007-08-26?21:54??用DSP進行mp3解壓縮的算法原程序

-----------?---------??----------?-----??----

???????????????119119????????????????????9