subband.c

著名的 helix realplayer 基于手机 symbian 系统的 播放器全套源代码

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/**************************************************************************************
 * Fixed-point MP3 decoder using Intel IPP libraries
 * June 2003
 *
 * subband.c - wrapper for IPP primitive which runs synthesis filter
 **************************************************************************************/

#include "coder.h"	

#define BLOCK_SIZE	18
#define	NBANDS		32

/**************************************************************************************
 * Function:    Subband
 *
 * Description: do subband transform on all the blocks in one granule, all channels
 *
 * Inputs:      filled MP3DecInfo structure, after calling IMDCT for all channels
 *              vbuf[ch] and vindex[ch] must be preserved between calls
 *
 * Outputs:     decoded PCM data, interleaved LRLRLR... if stereo
 *
 * Return:      0 on success,  -1 if null input pointers
 **************************************************************************************/
int Subband(MP3DecInfo *mp3DecInfo, short *pcmBuf)
{
	int b, ch, iMode;
	short *pcmPtr;
	IMDCTInfo *mi;
	SubbandInfo *sbi;

	/* validate pointers */
	if (!mp3DecInfo || !mp3DecInfo->IMDCTInfoPS || !mp3DecInfo->SubbandInfoPS)
		return -1;

	mi = (IMDCTInfo *)(mp3DecInfo->IMDCTInfoPS);
	sbi = (SubbandInfo*)(mp3DecInfo->SubbandInfoPS);

	iMode = (mp3DecInfo->nChans == 1 ? 1 : 2);
	for (ch = 0; ch < mp3DecInfo->nChans; ch++) {
		/* IPP primitive #7 - subband transform 
		 *   mode 2 means output samples are skipped by 2 (fills pcmBuf[0, 2, 4...])
		 *    - for stereo, we start at &pcmBuf[0] first time (L) and &pcmBuf[1] second time (R)
		 *    - for mono, we still use mode 1 (no interleaving)
		 */
		pcmPtr = pcmBuf + ch;		/* offset for stereo interleaving */
		for(b = 0; b < BLOCK_SIZE; b++) {
			ippsSynthPQMF_MP3_32s16s(mi->outBuf[ch] + b*NBANDS,	pcmPtr, sbi->vbuf[ch], &(sbi->vindex[ch]), iMode);
			pcmPtr += NBANDS * mp3DecInfo->nChans;
		}
	}

	return 0;
}