huffman.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
 *
 * huffman.c - wrapper for IPP primitive which decodes Huffman codewords
 **************************************************************************************/

#include "coder.h"	

/**************************************************************************************
 * Function:    DecodeHuffman
 *
 * Description: decode one granule, one channel worth of Huffman codes
 *
 * Inputs:      MP3DecInfo structure filled by UnpackFrameHeader(), UnpackSideInfo(),
 *                and UnpackScaleFactors() (for this granule)
 *              buffer pointing to start of Huffman data in MP3 frame
 *              pointer to bit offset (0-7) indicating starting bit in buf[0]
 *              number of bits in the Huffman data section of the frame
 *                (could include padding bits)
 *              index of current granule and channel
 *
 * Outputs:     decoded coefficients in hi->huffDecBuf[ch] (hi pointer in mp3DecInfo)
 *              updated bitOffset
 *
 * Return:      length (in bytes) of frame header (for caller to calculate offset to
 *                first byte following frame header)
 *              bitOffset also returned in parameter (0 = MSB, 7 = LSB of 
 *                byte located at buf + offset)
 *              -1 if null input pointers
 **************************************************************************************/
int DecodeHuffman(MP3DecInfo *mp3DecInfo, unsigned char *buf, int *bitOffset, int huffBlockBits, int gr, int ch)
{
	Ipp8u *pBitStream;
	FrameHeader *fh;
	IppMP3FrameHeader *fhIPP;
	SideInfo *si;
	IppMP3SideInfo *siIPP;
	HuffmanInfo *hi;

	/* validate pointers */
	if (!mp3DecInfo || !mp3DecInfo->FrameHeaderPS || !mp3DecInfo->SideInfoPS || !mp3DecInfo->HuffmanInfoPS)
		return -1;

	pBitStream = (Ipp8u *)buf;
	fh = (FrameHeader *)(mp3DecInfo->FrameHeaderPS);
	fhIPP = &(fh->fhIPP);

	/* si is an array of up to 4 structs, stored as gr0ch0, gr0ch1, gr1ch0, gr1ch1 */
	si = (SideInfo *)(mp3DecInfo->SideInfoPS);
	siIPP = &(si->siIPP[0]);
	siIPP += (gr*mp3DecInfo->nChans + ch);

	hi = (HuffmanInfo*)(mp3DecInfo->HuffmanInfoPS);

	/* IPP primitive #4 - Huffman decoding */
	ippsHuffmanDecode_MP3_1u32s(&pBitStream, bitOffset, hi->huffDecBuf[ch], &(hi->nonZeroBound[ch]), 
		siIPP, fhIPP, huffBlockBits);

	/* IPP primitive updated pBitStream, return the offset to start of next block in bitstream */
	return (pBitStream - buf);
}