[picodrive.git] / platform / common / mp3.c

/*
 * PicoDrive
 * (C) notaz, 2010
 *
 * This work is licensed under the terms of MAME license.
 * See COPYING file in the top-level directory.
 */
#include "mp3.h"

int mp3_find_sync_word(const unsigned char *buf, int size)
{
	const unsigned char *p, *pe;

	/* find byte-aligned syncword - need 12 (MPEG 1,2) or 11 (MPEG 2.5) matching bits */
	for (p = buf, pe = buf + size - 3; p <= pe; p++)
	{
		int pn;
		if (p[0] != 0xff)
			continue;
		pn = p[1];
		if ((pn & 0xf8) != 0xf8 || // currently must be MPEG1
		    (pn & 6) == 0) {       // invalid layer
			p++; continue;
		}
		pn = p[2];
		if ((pn & 0xf0) < 0x20 || (pn & 0xf0) == 0xf0 || // bitrates
		    (pn & 0x0c) != 0) { // not 44kHz
			continue;
		}

		return p - buf;
	}

	return -1;
}
Commit	Line	Data
cff531af	1	/*
	2	* PicoDrive
	3	* (C) notaz, 2010
	4	*
	5	* This work is licensed under the terms of MAME license.
	6	* See COPYING file in the top-level directory.
	7	*/
7c18e34a	8	#include "mp3.h"
	9
	10	int mp3_find_sync_word(const unsigned char *buf, int size)
	11	{
	12	const unsigned char p, pe;
	13
	14	/* find byte-aligned syncword - need 12 (MPEG 1,2) or 11 (MPEG 2.5) matching bits */
	15	for (p = buf, pe = buf + size - 3; p <= pe; p++)
	16	{
	17	int pn;
	18	if (p[0] != 0xff)
	19	continue;
	20	pn = p[1];
	21	if ((pn & 0xf8) != 0xf8 \|\| // currently must be MPEG1
	22	(pn & 6) == 0) { // invalid layer
	23	p++; continue;
	24	}
	25	pn = p[2];
	26	if ((pn & 0xf0) < 0x20 \|\| (pn & 0xf0) == 0xf0 \|\| // bitrates
	27	(pn & 0x0c) != 0) { // not 44kHz
	28	continue;
	29	}
	30
	31	return p - buf;
	32	}
	33
	34	return -1;
	35	}
	36