www.pudn.com > mp3rar.rar > huffdec3.c

/************************* MPEG-2 NBC Audio Decoder ************************** 
 *                                                                           * 
"This software module was originally developed by  
AT&T, Dolby Laboratories, Fraunhofer Gesellschaft IIS in the course of  
development of the MPEG-2 NBC/MPEG-4 Audio standard ISO/IEC 13818-7,  
14496-1,2 and 3. This software module is an implementation of a part of one or more  
MPEG-2 NBC/MPEG-4 Audio tools as specified by the MPEG-2 NBC/MPEG-4  
Audio standard. ISO/IEC  gives users of the MPEG-2 NBC/MPEG-4 Audio  
standards free license to this software module or modifications thereof for use in  
hardware or software products claiming conformance to the MPEG-2 NBC/MPEG-4 
Audio  standards. Those intending to use this software module in hardware or  
software products are advised that this use may infringe existing patents.  
The original developer of this software module and his/her company, the subsequent  
editors and their companies, and ISO/IEC have no liability for use of this software  
module or modifications thereof in an implementation. Copyright is not released for  
non MPEG-2 NBC/MPEG-4 Audio conforming products.The original developer 
retains full right to use the code for his/her  own purpose, assign or donate the  
code to a third party and to inhibit third party from using the code for non  
MPEG-2 NBC/MPEG-4 Audio conforming products. This copyright notice must 
be included in all copies or derivative works."  
Copyright(c)1996. 
 *                                                                           * 
 ****************************************************************************/ 
 
#include "all.h" 
 
 
int __cdecl 
huffcmp(const void *va, const void *vb) 
{ 
    const Huffman *a, *b; 
 
    a = (Huffman *)va; 
    b = (Huffman *)vb; 
    if (a->len < b->len) 
	return -1; 
    if ( (a->len == b->len) && (a->cw < b->cw) ) 
	return -1; 
    return 1; 
} 
 
/* 
 * initialize the Hcb structure and sort the Huffman 
 * codewords by length, shortest (most probable) first 
 */ 
void 
hufftab(Hcb *hcb, Huffman *hcw, int dim, int lav, int signed_cb) 
{ 
    int i, n; 
     
    if (!signed_cb) { 
	hcb->mod = lav + 1; 
        hcb->off = 0; 
    } 
    else { 
	hcb->mod = 2*lav + 1; 
        hcb->off = lav; 
    } 
    n=1;	     
    for (i=0; imod; 
    hcb->n = n; 
    hcb->dim = dim; 
    hcb->lav = lav; 
    hcb->signed_cb = signed_cb; 
    hcb->hcw = hcw; 
 
    qsort(hcw, n, sizeof(Huffman), huffcmp); 
} 
  
/* 
 * Cword is working buffer to which shorts from 
 *   bitstream are written. Bits are read from msb to lsb 
 * Nbits is number of lsb bits not yet consumed 
 *  
 * this uses a minimum-memory method of Huffman decoding 
 */ 
int 
decode_huff_cw(Huffman *h) 
{ 
    int i, j; 
    long cw; 
 
    i = h->len; 
    cw = getbits(i); 
    while ((unsigned long)cw != h->cw) { 
	h++; 
	j = h->len-i; 
	i += j; 
	cw <<= j; 
	cw |= getbits(j); 
    } 
    return(h->index); 
} 
 
 
void 
unpack_idx(int *qp, int idx, Hcb *hcb) 
{ 
    int dim = hcb->dim; 
    int mod = hcb->mod; 
    int off = hcb->off; 
    if(dim == 4){ 
	qp[0] = (idx/(mod*mod*mod)) - off; 
	idx -= (qp[0] + off)*(mod*mod*mod); 
	qp[1] = (idx/(mod*mod)) - off; 
	idx -= (qp[1] + off)*(mod*mod); 
	qp[2] = (idx/(mod)) - off; 
	idx -= (qp[2] + off)*(mod); 
	qp[3] = (idx) - off; 
    } 
    else { 
	qp[0] = (idx/(mod)) - off; 
	idx -= (qp[0] + off)*(mod); 
	qp[1] = (idx) - off; 
    } 
} 
 
/* get sign bits */ 
void 
get_sign_bits(int *q, int n) 
{ 
    int i; 
 
    if(nbits <= 16) { 
		cword = (cword<<16) | getshort(); 
		nbits += 16; 
    } 
    for (i=0; i> nbits) & 1) { 
				/* 1 signals negative, as in 2's complement */ 
				q[i] = -q[i]; 
			} 
		} 
    } 
}