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/* ---- DXhead.c --------------------------------------------
*
*
* decoder MPEG Layer III handle Xing header
*
* mod 12/7/98 add vbr scale
*
* Copyright 1998 Xing Technology Corp.
* -----------------------------------------------------------
*/
#include <stdlib.h>
#include <stdio.h>
#include <float.h>
#include <math.h>
#include "dxhead.h"
/* 4 Xing
* 4 flags
* 4 frames
* 4 bytes
* 100 toc
*/
/*-------------------------------------------------------------*/
static int ExtractI4(unsigned char *buf)
{
int x;
/* big endian extract */
x = buf[0];
x <<= 8;
x |= buf[1];
x <<= 8;
x |= buf[2];
x <<= 8;
x |= buf[3];
return x;
}
/*-------------------------------------------------------------*/
int mpg123_get_xing_header(XHEADDATA * X, unsigned char *buf)
{
int i, head_flags;
int h_id, h_mode, h_sr_index;
static int sr_table[4] =
{44100, 48000, 32000, 99999};
/* get Xing header data */
X->flags = 0; /* clear to null incase fail */
/* get selected MPEG header data */
h_id = (buf[1] >> 3) & 1;
h_sr_index = (buf[2] >> 2) & 3;
h_mode = (buf[3] >> 6) & 3;
/* determine offset of header */
if (h_id)
{ /* mpeg1 */
if (h_mode != 3)
buf += (32 + 4);
else
buf += (17 + 4);
}
else
{ /* mpeg2 */
if (h_mode != 3)
buf += (17 + 4);
else
buf += (9 + 4);
}
if (buf[0] != 'X')
return 0; /* fail */
if (buf[1] != 'i')
return 0; /* header not found */
if (buf[2] != 'n')
return 0;
if (buf[3] != 'g')
return 0;
buf += 4;
X->h_id = h_id;
X->samprate = sr_table[h_sr_index];
if (h_id == 0)
X->samprate >>= 1;
head_flags = X->flags = ExtractI4(buf);
buf += 4; /* get flags */
if (head_flags & FRAMES_FLAG)
{
X->frames = ExtractI4(buf);
buf += 4;
}
if (head_flags & BYTES_FLAG)
{
X->bytes = ExtractI4(buf);
buf += 4;
}
if (head_flags & TOC_FLAG)
{
if (X->toc != NULL)
{
for (i = 0; i < 100; i++)
X->toc[i] = buf[i];
}
buf += 100;
}
X->vbr_scale = -1;
if (head_flags & VBR_SCALE_FLAG)
{
X->vbr_scale = ExtractI4(buf);
buf += 4;
}
/*if( X->toc != NULL ) {
*for(i=0;i<100;i++) {
* if( (i%10) == 0 ) printf("\n");
* printf(" %3d", (int)(X->toc[i]));
*}
*}
*/
return 1; /* success */
}
/*-------------------------------------------------------------*/
int mpg123_seek_point(unsigned char TOC[100], int file_bytes, float percent)
{
/* interpolate in TOC to get file seek point in bytes */
int a, seekpoint;
float fa, fb, fx;
if (percent < 0.0f)
percent = 0.0f;
if (percent > 100.0f)
percent = 100.0f;
a = (int) percent;
if (a > 99)
a = 99;
fa = TOC[a];
if (a < 99)
{
fb = TOC[a + 1];
}
else
{
fb = 256.0f;
}
fx = fa + (fb - fa) * (percent - a);
seekpoint = (int) ((1.0f / 256.0f) * fx * file_bytes);
return seekpoint;
}
/*-------------------------------------------------------------*/
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