/*---- 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;
	
}

/*-------------------------------------------------------------*/ 
