/*
	parse: spawned from common; clustering around stream/frame parsing

	copyright ?-2014 by the mpg123 project - free software under the terms of the LGPL 2.1
	see COPYING and AUTHORS files in distribution or http://mpg123.org
	initially written by Michael Hipp & Thomas Orgis
*/

#include "mpg123lib_intern.h"

#include <sys/stat.h>
#include <fcntl.h>

#include "getbits.h"

#if defined (WANT_WIN32_SOCKETS)
#include <winsock2.h>
#include <ws2tcpip.h>
#endif

/* a limit for number of frames in a track; beyond that unsigned long may not be enough to hold byte addresses */
#ifdef HAVE_LIMITS_H
#include <limits.h>
#endif
#ifndef ULONG_MAX
/* hm, is this portable across preprocessors? */
#define ULONG_MAX ((unsigned long)-1)
#endif
#define TRACK_MAX_FRAMES ULONG_MAX/4/1152

#include "mpeghead.h"

#include "debug.h"

#define bsbufid(fr) (fr)->bsbuf==(fr)->bsspace[0] ? 0 : ((fr)->bsbuf==fr->bsspace[1] ? 1 : ( (fr)->bsbuf==(fr)->bsspace[0]+512 ? 2 : ((fr)->bsbuf==fr->bsspace[1]+512 ? 3 : -1) ) )

/* PARSE_GOOD and PARSE_BAD have to be 1 and 0 (TRUE and FALSE), others can vary. */
enum parse_codes
{
	 PARSE_MORE = MPG123_NEED_MORE
	,PARSE_ERR  = MPG123_ERR
	,PARSE_END  = 10 /* No more audio data to find. */
	,PARSE_GOOD = 1 /* Everything's fine. */
	,PARSE_BAD  = 0 /* Not fine (invalid data). */
	,PARSE_RESYNC = 2 /* Header not good, go into resync. */
	,PARSE_AGAIN  = 3 /* Really start over, throw away and read a new header, again. */
};

/* bitrates for [mpeg1/2][layer] */
static const int tabsel_123[2][3][16] =
{
	{
		{0,32,64,96,128,160,192,224,256,288,320,352,384,416,448,},
		{0,32,48,56, 64, 80, 96,112,128,160,192,224,256,320,384,},
		{0,32,40,48, 56, 64, 80, 96,112,128,160,192,224,256,320,}
	},
	{
		{0,32,48,56,64,80,96,112,128,144,160,176,192,224,256,},
		{0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,},
		{0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,}
	}
};

static const long freqs[9] = { 44100, 48000, 32000, 22050, 24000, 16000 , 11025 , 12000 , 8000 };

static int decode_header(mpg123_handle *fr,unsigned long newhead, int *freeformat_count);
static int skip_junk(mpg123_handle *fr, unsigned long *newheadp, long *headcount);
static int do_readahead(mpg123_handle *fr, unsigned long newhead);
static int wetwork(mpg123_handle *fr, unsigned long *newheadp);

/* These two are to be replaced by one function that gives all the frame parameters (for outsiders).*/
/* Those functions are unsafe regarding bad arguments (inside the mpg123_handle), but just returning anything would also be unsafe, the caller code has to be trusted. */

int frame_bitrate(mpg123_handle *fr)
{
	return tabsel_123[fr->lsf][fr->lay-1][fr->bitrate_index];
}

long frame_freq(mpg123_handle *fr)
{
	return freqs[fr->sampling_frequency];
}

/* compiler is smart enought to inline this one or should I really do it as macro...? */
static int head_check(unsigned long head)
{
	if
	(
		((head & HDR_SYNC) != HDR_SYNC)
		||
		/* layer: 01,10,11 is 1,2,3; 00 is reserved */
		(!(HDR_LAYER_VAL(head)))
		||
		/* 1111 means bad bitrate */
		(HDR_BITRATE_VAL(head) == 0xf)
		||
		/* sampling freq: 11 is reserved */
		(HDR_SAMPLERATE_VAL(head) == 0x3)
		/* here used to be a mpeg 2.5 check... re-enabled 2.5 decoding due to lack of evidence that it is really not good */
	)
	{
		return FALSE;
	}
	/* if no check failed, the header is valid (hopefully)*/
	else
	{
		return TRUE;
	}
}

static int check_lame_tag(mpg123_handle *fr)
{
	/*
		going to look for Xing or Info at some position after the header
		                                   MPEG 1  MPEG 2/2.5 (LSF)
		Stereo, Joint Stereo, Dual Channel  32      17
		Mono                                17       9

		Also, how to avoid false positives? I guess I should interpret more of the header to rule that out(?).
		I hope that ensuring all zeros until tag start is enough.
	*/
	int lame_offset = (fr->stereo == 2) ? (fr->lsf ? 17 : 32 ) : (fr->lsf ? 9 : 17);

	if(fr->p.flags & MPG123_IGNORE_INFOFRAME) return 0;

	/* Note: CRC or not, that does not matter here. */
	if(fr->framesize >= 120+lame_offset) /* traditional Xing header is 120 bytes */
	{
		int i;
		int lame_type = 0;
		debug("do we have lame tag?");
		/* only search for tag when all zero before it (apart from checksum) */
		for(i=2; i < lame_offset; ++i) if(fr->bsbuf[i] != 0) break;
		if(i == lame_offset)
		{
			debug("possibly...");
			if
			(
					   (fr->bsbuf[lame_offset] == 'I')
				&& (fr->bsbuf[lame_offset+1] == 'n')
				&& (fr->bsbuf[lame_offset+2] == 'f')
				&& (fr->bsbuf[lame_offset+3] == 'o')
			)
			{
				lame_type = 1; /* We still have to see what there is */
			}
			else if
			(
					   (fr->bsbuf[lame_offset] == 'X')
				&& (fr->bsbuf[lame_offset+1] == 'i')
				&& (fr->bsbuf[lame_offset+2] == 'n')
				&& (fr->bsbuf[lame_offset+3] == 'g')
			)
			{
				lame_type = 2;
				fr->vbr = MPG123_VBR; /* Xing header means always VBR */
			}
			if(lame_type)
			{
				unsigned long xing_flags;

				/* we have one of these headers... */
				if(VERBOSE2) fprintf(stderr, "Note: Xing/Lame/Info header detected\n");
				/* now interpret the Xing part, I have 120 bytes total for sure */
				/* there are 4 bytes for flags, but only the last byte contains known ones */
				lame_offset += 4; /* now first byte after Xing/Name */
				/* 4 bytes dword for flags */
				#define make_long(a, o) ((((unsigned long) a[o]) << 24) | (((unsigned long) a[o+1]) << 16) | (((unsigned long) a[o+2]) << 8) | ((unsigned long) a[o+3]))
				/* 16 bit */
				#define make_short(a,o) ((((unsigned short) a[o]) << 8) | ((unsigned short) a[o+1]))
				xing_flags = make_long(fr->bsbuf, lame_offset);
				lame_offset += 4;
				debug1("Xing: flags 0x%08lx", xing_flags);
				if(xing_flags & 1) /* frames */
				{
					if(fr->p.flags & MPG123_IGNORE_STREAMLENGTH)
					{
						if(VERBOSE3)
						fprintf(stderr, "Note: Ignoring Xing frames because of MPG123_IGNORE_STREAMLENGTH\n");
					}
					else
					{
						fr->track_frames = (off_t) make_long(fr->bsbuf, lame_offset);
						if(fr->track_frames > TRACK_MAX_FRAMES) fr->track_frames = 0; /* endless stream? */
#ifdef GAPLESS
						/* All or nothing: Only if encoder delay/padding is known we'll cut samples for gapless. */
						if(fr->p.flags & MPG123_GAPLESS)
						frame_gapless_init(fr, fr->track_frames, 0, 0);
#endif
						if(VERBOSE3) fprintf(stderr, "Note: Xing: %lu frames\n", (long unsigned)fr->track_frames);
					}

					lame_offset += 4;
				}
				if(xing_flags & 0x2) /* bytes */
				{
					if(fr->p.flags & MPG123_IGNORE_STREAMLENGTH)
					{
						if(VERBOSE3)
						fprintf(stderr, "Note: Ignoring Xing bytes because of MPG123_IGNORE_STREAMLENGTH\n");
					}
					else
					{
						unsigned long xing_bytes = make_long(fr->bsbuf, lame_offset);					/* We assume that this is the _total_ size of the file, including Xing frame ... and ID3 frames...
						   It's not that clearly documented... */
						if(fr->rdat.filelen < 1)
						fr->rdat.filelen = (off_t) xing_bytes; /* One could start caring for overflow here. */
						else
						{
							if((off_t) xing_bytes != fr->rdat.filelen && NOQUIET)
							{
								double diff = 1.0/fr->rdat.filelen * (fr->rdat.filelen - (off_t)xing_bytes);
								if(diff < 0.) diff = -diff;

								if(VERBOSE3)
								fprintf(stderr, "Note: Xing stream size %lu differs by %f%% from determined/given file size!\n", xing_bytes, diff);

								if(diff > 1.)
								fprintf(stderr, "Warning: Xing stream size off by more than 1%%, fuzzy seeking may be even more fuzzy than by design!\n");
							}
						}

						if(VERBOSE3)
						fprintf(stderr, "Note: Xing: %lu bytes\n", (long unsigned)xing_bytes);
					}

					lame_offset += 4;
				}
				if(xing_flags & 0x4) /* TOC */
				{
					frame_fill_toc(fr, fr->bsbuf+lame_offset);
					lame_offset += 100; /* just skip */
				}
				if(xing_flags & 0x8) /* VBR quality */
				{
					if(VERBOSE3)
					{
						unsigned long xing_quality = make_long(fr->bsbuf, lame_offset);
						fprintf(stderr, "Note: Xing: quality = %lu\n", (long unsigned)xing_quality);
					}
					lame_offset += 4;
				}
				/* I guess that either 0 or LAME extra data follows */
				if(fr->bsbuf[lame_offset] != 0)
				{
					unsigned char lame_vbr;
					float replay_gain[2] = {0,0};
					float peak = 0;
					float gain_offset = 0; /* going to be +6 for old lame that used 83dB */
					char nb[10];
					memcpy(nb, fr->bsbuf+lame_offset, 9);
					nb[9] = 0;
					if(VERBOSE3) fprintf(stderr, "Note: Info: Encoder: %s\n", nb);
					if(!strncmp("LAME", nb, 4))
					{
						/* Lame versions before 3.95.1 used 83 dB reference level, later versions 89 dB.
						   We stick with 89 dB as being "normal", adding 6 dB. */
						unsigned int major, minor;
						char rest[6];
						rest[0] = 0;
						if(sscanf(nb+4, "%u.%u%s", &major, &minor, rest) >= 2)
						{
							debug3("LAME: %u/%u/%s", major, minor, rest);
							/* We cannot detect LAME 3.95 reliably (same version string as 3.95.1), so this is a blind spot.
							   Everything < 3.95 is safe, though. */
							if(major < 3 || (major == 3 && minor < 95))  /* || (major == 3 && minor == 95 && rest[0] == 0)) */
							{
								gain_offset = 6;
								if(VERBOSE3) fprintf(stderr, "Note: Info: Old LAME detected, using ReplayGain preamp of %f dB.\n", gain_offset);
							}
						}
						else if(VERBOSE3) fprintf(stderr, "Note: Info: Cannot determine LAME version.\n");
					}
					lame_offset += 9;
					/* the 4 big bits are tag revision, the small bits vbr method */
					lame_vbr = fr->bsbuf[lame_offset] & 15;
					if(VERBOSE3)
					{
						fprintf(stderr, "Note: Info: rev %u\n", fr->bsbuf[lame_offset] >> 4);
						fprintf(stderr, "Note: Info: vbr mode %u\n", lame_vbr);
					}
					lame_offset += 1;
					switch(lame_vbr)
					{
						/* from rev1 proposal... not sure if all good in practice */
						case 1:
						case 8: fr->vbr = MPG123_CBR; break;
						case 2:
						case 9: fr->vbr = MPG123_ABR; break;
						default: fr->vbr = MPG123_VBR; /* 00==unknown is taken as VBR */
					}
					/* skipping: lowpass filter value */
					lame_offset += 1;
					/* replaygain */
					/* 32bit float: peak amplitude -- why did I parse it as int before??*/
					/* Ah, yes, lame seems to store it as int since some day in 2003; I've only seen zeros anyway until now, bah! */
					if
					(
							 (fr->bsbuf[lame_offset] != 0)
						|| (fr->bsbuf[lame_offset+1] != 0)
						|| (fr->bsbuf[lame_offset+2] != 0)
						|| (fr->bsbuf[lame_offset+3] != 0)
					)
					{
						debug("Wow! Is there _really_ a non-zero peak value? Now is it stored as float or int - how should I know?");
						/* byte*peak_bytes = (byte*) &peak;
						... endianess ... just copy bytes to avoid floating point operation on unaligned memory?
						peak_bytes[0] = ...
						peak = *(float*) (fr->bsbuf+lame_offset); */
					}
					if(VERBOSE3) fprintf(stderr, "Note: Info: peak = %f (I won't use this)\n", peak);
					peak = 0; /* until better times arrived */
					lame_offset += 4;
					/*
						ReplayGain values - lame only writes radio mode gain...
						16bit gain, 3 bits name, 3 bits originator, sign (1=-, 0=+), dB value*10 in 9 bits (fixed point)
						ignore the setting if name or originator == 000!
						radio 0 0 1 0 1 1 1 0 0 1 1 1 1 1 0 1
						audiophile 0 1 0 0 1 0 0 0 0 0 0 1 0 1 0 0
					*/

					for(i =0; i < 2; ++i)
					{
						unsigned char origin = (fr->bsbuf[lame_offset] >> 2) & 0x7; /* the 3 bits after that... */
						if(origin != 0)
						{
							unsigned char gt = fr->bsbuf[lame_offset] >> 5; /* only first 3 bits */
							if(gt == 1) gt = 0; /* radio */
							else if(gt == 2) gt = 1; /* audiophile */
							else continue;
							/* get the 9 bits into a number, divide by 10, multiply sign... happy bit banging */
							replay_gain[gt] = (float) ((fr->bsbuf[lame_offset] & 0x2) ? -0.1 : 0.1) * (make_short(fr->bsbuf, lame_offset) & 0x1ff);
							/* If this is an automatic value from LAME (or whatever), the automatic gain offset applies.
							   If a user or whoever set the value, do not touch it! 011 is automatic origin. */
							if(origin == 3) replay_gain[gt] += gain_offset;
						}
						lame_offset += 2;
					}
					if(VERBOSE3) 
					{
						fprintf(stderr, "Note: Info: Radio Gain = %03.1fdB\n", replay_gain[0]);
						fprintf(stderr, "Note: Info: Audiophile Gain = %03.1fdB\n", replay_gain[1]);
					}
					for(i=0; i < 2; ++i)
					{
						if(fr->rva.level[i] <= 0)
						{
							fr->rva.peak[i] = 0; /* at some time the parsed peak should be used */
							fr->rva.gain[i] = replay_gain[i];
							fr->rva.level[i] = 0;
						}
					}
					lame_offset += 1; /* skipping encoding flags byte */
					if(fr->vbr == MPG123_ABR)
					{
						fr->abr_rate = fr->bsbuf[lame_offset];
						if(VERBOSE3) fprintf(stderr, "Note: Info: ABR rate = %u\n", fr->abr_rate);
					}
					lame_offset += 1;
					/* encoder delay and padding, two 12 bit values... lame does write them from int ...*/
					if(VERBOSE3)
					fprintf(stderr, "Note: Encoder delay = %i; padding = %i\n",
					        ((((int) fr->bsbuf[lame_offset]) << 4) | (((int) fr->bsbuf[lame_offset+1]) >> 4)),
					        (((((int) fr->bsbuf[lame_offset+1]) << 8) | (((int) fr->bsbuf[lame_offset+2]))) & 0xfff) );
					#ifdef GAPLESS
					if(fr->p.flags & MPG123_GAPLESS)
					{
						off_t skipbegin = ((((int) fr->bsbuf[lame_offset]) << 4) | (((int) fr->bsbuf[lame_offset+1]) >> 4));
						off_t skipend = (((((int) fr->bsbuf[lame_offset+1]) << 8) | (((int) fr->bsbuf[lame_offset+2]))) & 0xfff);
						frame_gapless_init(fr, fr->track_frames, skipbegin, skipend);
					}
					#endif
				}
				/* switch buffer back ... */
				fr->bsbuf = fr->bsspace[fr->bsnum]+512;
				fr->bsnum = (fr->bsnum + 1) & 1;
				return 1; /* got it! */
			}
		}
	}
	return 0; /* no lame tag */
}

/* Just tell if the header is some mono. */
static int header_mono(unsigned long newhead)
{
	return HDR_CHANNEL_VAL(newhead) == MPG_MD_MONO ? TRUE : FALSE;
}

/* true if the two headers will work with the same decoding routines */
static int head_compatible(unsigned long fred, unsigned long bret)
{
	return ( (fred & HDR_CMPMASK) == (bret & HDR_CMPMASK)
		&&       header_mono(fred) == header_mono(bret)    );
}

static void halfspeed_prepare(mpg123_handle *fr)
{
	/* save for repetition */
	if(fr->p.halfspeed && fr->lay == 3)
	{
		debug("halfspeed - reusing old bsbuf ");
		memcpy (fr->ssave, fr->bsbuf, fr->ssize);
	}
}

/* If this returns 1, the next frame is the repetition. */
static int halfspeed_do(mpg123_handle *fr)
{
	/* Speed-down hack: Play it again, Sam (the frame, I mean). */
	if (fr->p.halfspeed) 
	{
		if(fr->halfphase) /* repeat last frame */
		{
			debug("repeat!");
			fr->to_decode = fr->to_ignore = TRUE;
			--fr->halfphase;
			fr->bitindex = 0;
			fr->wordpointer = (unsigned char *) fr->bsbuf;
			if(fr->lay == 3) memcpy (fr->bsbuf, fr->ssave, fr->ssize);
			if(fr->error_protection) fr->crc = getbits(fr, 16); /* skip crc */
			return 1;
		}
		else
		{
			fr->halfphase = fr->p.halfspeed - 1;
		}
	}
	return 0;
}

/* 
	Temporary macro until we got this worked out.
	Idea is to filter out special return values that shall trigger direct jumps to end / resync / read again. 
	Particularily, the generic ret==PARSE_BAD==0 and ret==PARSE_GOOD==1 are not affected.
*/
#define JUMP_CONCLUSION(ret) \
{ \
if(ret < 0){ debug1("%s", ret == MPG123_NEED_MORE ? "need more" : "read error"); goto read_frame_bad; } \
else if(ret == PARSE_AGAIN) goto read_again; \
else if(ret == PARSE_RESYNC) goto init_resync; \
else if(ret == PARSE_END){ ret=0; goto read_frame_bad; } \
}

/*
	That's a big one: read the next frame. 1 is success, <= 0 is some error
	Special error READER_MORE means: Please feed more data and try again.
*/
int read_frame(mpg123_handle *fr)
{
	/* TODO: rework this thing */
	int freeformat_count = 0;
	unsigned long newhead;
	off_t framepos;
	int ret;
	/* stuff that needs resetting if complete frame reading fails */
	int oldsize  = fr->framesize;
	int oldphase = fr->halfphase;

	/* The counter for the search-first-header loop.
	   It is persistent outside the loop to prevent seemingly endless loops
	   when repeatedly headers are found that do not have valid followup headers. */
	long headcount = 0;

	fr->fsizeold=fr->framesize;       /* for Layer3 */

	if(halfspeed_do(fr) == 1) return 1;

read_again:
	/* In case we are looping to find a valid frame, discard any buffered data before the current position.
	   This is essential to prevent endless looping, always going back to the beginning when feeder buffer is exhausted. */
	if(fr->rd->forget != NULL) fr->rd->forget(fr);

	debug2("trying to get frame %"OFF_P" at %"OFF_P, (off_p)fr->num+1, (off_p)fr->rd->tell(fr));
	if((ret = fr->rd->head_read(fr,&newhead)) <= 0){ debug1("need more? (%i)", ret); goto read_frame_bad;}

init_resync:

#ifdef SKIP_JUNK
	if(!fr->firsthead && !head_check(newhead))
	{
		ret = skip_junk(fr, &newhead, &headcount);
		JUMP_CONCLUSION(ret);
	}
#endif

	ret = head_check(newhead);
	if(ret) ret = decode_header(fr, newhead, &freeformat_count);

	JUMP_CONCLUSION(ret); /* That only continues for ret == PARSE_BAD or PARSE_GOOD. */
	if(ret == PARSE_BAD)
	{ /* Header was not good. */
		ret = wetwork(fr, &newhead); /* Messy stuff, handle junk, resync ... */
		JUMP_CONCLUSION(ret);
		/* Normally, we jumped already. If for some reason everything's fine to continue, do continue. */
		if(ret != PARSE_GOOD) goto read_frame_bad;
	}

	if(!fr->firsthead)
	{
		ret = do_readahead(fr, newhead);
		/* readahead can fail mit NEED_MORE, in which case we must also make the just read header available again for next go */
		if(ret < 0) fr->rd->back_bytes(fr, 4);
		JUMP_CONCLUSION(ret);
	}

	/* Now we should have our valid header and proceed to reading the frame. */

	/* if filepos is invalid, so is framepos */
	framepos = fr->rd->tell(fr) - 4;
	/* flip/init buffer for Layer 3 */
	{
		unsigned char *newbuf = fr->bsspace[fr->bsnum]+512;
		/* read main data into memory */
		if((ret=fr->rd->read_frame_body(fr,newbuf,fr->framesize))<0)
		{
			/* if failed: flip back */
			debug("need more?");
			goto read_frame_bad;
		}
		fr->bsbufold = fr->bsbuf;
		fr->bsbuf = newbuf;
	}
	fr->bsnum = (fr->bsnum + 1) & 1;

	if(!fr->firsthead)
	{
		fr->firsthead = newhead; /* _now_ it's time to store it... the first real header */
		/* This is the first header of our current stream segment.
		   It is only the actual first header of the whole stream when fr->num is still below zero!
		   Think of resyncs where firsthead has been reset for format flexibility. */
		if(fr->num < 0)
		{
			fr->audio_start = framepos;
			/* Only check for LAME  tag at beginning of whole stream
			   ... when there indeed is one in between, it's the user's problem. */
			if(fr->lay == 3 && check_lame_tag(fr) == 1)
			{ /* ...in practice, Xing/LAME tags are layer 3 only. */
				if(fr->rd->forget != NULL) fr->rd->forget(fr);

				fr->oldhead = 0;
				goto read_again;
			}
			/* now adjust volume */
			do_rva(fr);
		}

		debug2("fr->firsthead: %08lx, audio_start: %li", fr->firsthead, (long int)fr->audio_start);
	}

  fr->bitindex = 0;
  fr->wordpointer = (unsigned char *) fr->bsbuf;
	/* Question: How bad does the floating point value get with repeated recomputation?
	   Also, considering that we can play the file or parts of many times. */
	if(++fr->mean_frames != 0)
	{
		fr->mean_framesize = ((fr->mean_frames-1)*fr->mean_framesize+compute_bpf(fr)) / fr->mean_frames ;
	}
	++fr->num; /* 0 for first frame! */
	debug4("Frame %"OFF_P" %08lx %i, next filepos=%"OFF_P, 
	(off_p)fr->num, newhead, fr->framesize, (off_p)fr->rd->tell(fr));
	if(!(fr->state_flags & FRAME_FRANKENSTEIN) && (
		(fr->track_frames > 0 && fr->num >= fr->track_frames)
#ifdef GAPLESS
		|| (fr->gapless_frames > 0 && fr->num >= fr->gapless_frames)
#endif
	))
	{
		fr->state_flags |= FRAME_FRANKENSTEIN;
		if(NOQUIET) fprintf(stderr, "\nWarning: Encountered more data after announced end of track (frame %"OFF_P"/%"OFF_P"). Frankenstein!\n", (off_p)fr->num, 
#ifdef GAPLESS
		fr->gapless_frames > 0 ? (off_p)fr->gapless_frames : 
#endif
		(off_p)fr->track_frames);
	}

	halfspeed_prepare(fr);

	/* index the position */
	fr->input_offset = framepos;
#ifdef FRAME_INDEX
	/* Keep track of true frame positions in our frame index.
	   but only do so when we are sure that the frame number is accurate... */
	if((fr->state_flags & FRAME_ACCURATE) && FI_NEXT(fr->index, fr->num))
	fi_add(&fr->index, framepos);
#endif

	if(fr->silent_resync > 0) --fr->silent_resync;

	if(fr->rd->forget != NULL) fr->rd->forget(fr);

	fr->to_decode = fr->to_ignore = TRUE;
	if(fr->error_protection) fr->crc = getbits(fr, 16); /* skip crc */

	/*
		Let's check for header change after deciding that the new one is good
		and actually having read a frame.

		header_change > 1: decoder structure has to be updated
		Preserve header_change value from previous runs if it is serious.
		If we still have a big change pending, it should be dealt with outside,
		fr->header_change set to zero afterwards.
	*/
	if(fr->header_change < 2)
	{
		fr->header_change = 2; /* output format change is possible... */
		if(fr->oldhead)        /* check a following header for change */
		{
			if(fr->oldhead == newhead) fr->header_change = 0;
			else
			/* Headers that match in this test behave the same for the outside world.
			   namely: same decoding routines, same amount of decoded data. */
			if(head_compatible(fr->oldhead, newhead))
			fr->header_change = 1;
			else
			{
				fr->state_flags |= FRAME_FRANKENSTEIN;
				if(NOQUIET)
				fprintf(stderr, "\nWarning: Big change (MPEG version, layer, rate). Frankenstein stream?\n");
			}
		}
		else if(fr->firsthead && !head_compatible(fr->firsthead, newhead))
		{
			fr->state_flags |= FRAME_FRANKENSTEIN;
			if(NOQUIET)
			fprintf(stderr, "\nWarning: Big change from first (MPEG version, layer, rate). Frankenstein stream?\n");
		}
	}

	fr->oldhead = newhead;

	return 1;
read_frame_bad:
	/* Also if we searched for valid data in vein, we can forget skipped data.
	   Otherwise, the feeder would hold every dead old byte in memory until the first valid frame! */
	if(fr->rd->forget != NULL) fr->rd->forget(fr);

	fr->silent_resync = 0;
	if(fr->err == MPG123_OK) fr->err = MPG123_ERR_READER;
	fr->framesize = oldsize;
	fr->halfphase = oldphase;
	/* That return code might be inherited from some feeder action, or reader error. */
	return ret;
}


/*
 * read ahead and find the next MPEG header, to guess framesize
 * return value: success code
 *  PARSE_GOOD: found a valid frame size (stored in the handle).
 * <0: error codes, possibly from feeder buffer (NEED_MORE)
 *  PARSE_BAD: cannot get the framesize for some reason and shall silentry try the next possible header (if this is no free format stream after all...)
 */
static int guess_freeformat_framesize(mpg123_handle *fr)
{
	long i;
	int ret;
	unsigned long head;
	if(!(fr->rdat.flags & (READER_SEEKABLE|READER_BUFFERED)))
	{
		if(NOQUIET) error("Cannot look for freeformat frame size with non-seekable and non-buffered stream!");

		return PARSE_BAD;
	}
	if((ret=fr->rd->head_read(fr,&head))<=0)
	return ret;

	/* We are already 4 bytes into it */
	for(i=4;i<MAXFRAMESIZE+4;i++)
	{
		if((ret=fr->rd->head_shift(fr,&head))<=0) return ret;

		/* No head_check needed, the mask contains all relevant bits. */
		if((head & HDR_SAMEMASK) == (fr->oldhead & HDR_SAMEMASK))
		{
			fr->rd->back_bytes(fr,i+1);
			fr->framesize = i-3;
			return PARSE_GOOD; /* Success! */
		}
	}
	fr->rd->back_bytes(fr,i);
	return PARSE_BAD;
}


/*
 * decode a header and write the information
 * into the frame structure
 * Return values are compatible with those of read_frame, namely:
 *  1: success
 *  0: no valid header
 * <0: some error
 * You are required to do a head_check() before calling!
 */
static int decode_header(mpg123_handle *fr,unsigned long newhead, int *freeformat_count)
{
#ifdef DEBUG /* Do not waste cycles checking the header twice all the time. */
	if(!head_check(newhead))
	{
		error1("trying to decode obviously invalid header 0x%08lx", newhead);
	}
#endif
	/* For some reason, the layer and sampling freq settings used to be wrapped
	   in a weird conditional including MPG123_NO_RESYNC. What was I thinking?
	   This information has to be consistent. */
	fr->lay = 4 - HDR_LAYER_VAL(newhead);

	if(HDR_VERSION_VAL(newhead) & 0x2)
	{
		fr->lsf = (HDR_VERSION_VAL(newhead) & 0x1) ? 0 : 1;
		fr->mpeg25 = 0;
		fr->sampling_frequency = HDR_SAMPLERATE_VAL(newhead) + (fr->lsf*3);
	}
	else
	{
		fr->lsf = 1;
		fr->mpeg25 = 1;
		fr->sampling_frequency = 6 + HDR_SAMPLERATE_VAL(newhead);
	}

	#ifdef DEBUG
	/* seen a file where this varies (old lame tag without crc, track with crc) */
	if((HDR_CRC_VAL(newhead)^0x1) != fr->error_protection) debug("changed crc bit!");
	#endif
	fr->error_protection = HDR_CRC_VAL(newhead)^0x1;
	fr->bitrate_index    = HDR_BITRATE_VAL(newhead);
	fr->padding          = HDR_PADDING_VAL(newhead);
	fr->extension        = HDR_PRIVATE_VAL(newhead);
	fr->mode             = HDR_CHANNEL_VAL(newhead);
	fr->mode_ext         = HDR_CHANEX_VAL(newhead);
	fr->copyright        = HDR_COPYRIGHT_VAL(newhead);
	fr->original         = HDR_ORIGINAL_VAL(newhead);
	fr->emphasis         = HDR_EMPHASIS_VAL(newhead);
	fr->freeformat       = !(newhead & HDR_BITRATE);

	fr->stereo = (fr->mode == MPG_MD_MONO) ? 1 : 2;

	/* we can't use tabsel_123 for freeformat, so trying to guess framesize... */
	if(fr->freeformat)
	{
		/* when we first encounter the frame with freeformat, guess framesize */
		if(fr->freeformat_framesize < 0)
		{
			int ret;
			*freeformat_count += 1;
			if(*freeformat_count > 5)
			{
				if(VERBOSE3) error("You fooled me too often. Refusing to guess free format frame size _again_.");
				return PARSE_BAD;
			}
			ret = guess_freeformat_framesize(fr);
			if(ret == PARSE_GOOD)
			{
				fr->freeformat_framesize = fr->framesize - fr->padding;
				if(VERBOSE2)
				fprintf(stderr, "Note: free format frame size %li\n", fr->freeformat_framesize);
			}
			else
			{
				if(ret == MPG123_NEED_MORE)
				debug("Need more data to guess free format frame size.");
				else if(VERBOSE3)
				error("Encountered free format header, but failed to guess frame size.");

				return ret;
			}
		}
		/* freeformat should be CBR, so the same framesize can be used at the 2nd reading or later */
		else
		{
			fr->framesize = fr->freeformat_framesize + fr->padding;
		}
	}

	switch(fr->lay)
	{
#ifndef NO_LAYER1
		case 1:
			fr->spf = 384;
			fr->do_layer = do_layer1;
			if(!fr->freeformat)
			{
				fr->framesize  = (long) tabsel_123[fr->lsf][0][fr->bitrate_index] * 12000;
				fr->framesize /= freqs[fr->sampling_frequency];
				fr->framesize  = ((fr->framesize+fr->padding)<<2)-4;
			}
		break;
#endif
#ifndef NO_LAYER2
		case 2:
			fr->spf = 1152;
			fr->do_layer = do_layer2;
			if(!fr->freeformat)
			{
				debug2("bitrate index: %i (%i)", fr->bitrate_index, tabsel_123[fr->lsf][1][fr->bitrate_index] );
				fr->framesize = (long) tabsel_123[fr->lsf][1][fr->bitrate_index] * 144000;
				fr->framesize /= freqs[fr->sampling_frequency];
				fr->framesize += fr->padding - 4;
			}
		break;
#endif
#ifndef NO_LAYER3
		case 3:
			fr->spf = fr->lsf ? 576 : 1152; /* MPEG 2.5 implies LSF.*/
			fr->do_layer = do_layer3;
			if(fr->lsf)
			fr->ssize = (fr->stereo == 1) ? 9 : 17;
			else
			fr->ssize = (fr->stereo == 1) ? 17 : 32;

			if(fr->error_protection)
			fr->ssize += 2;

			if(!fr->freeformat)
			{
				fr->framesize  = (long) tabsel_123[fr->lsf][2][fr->bitrate_index] * 144000;
				fr->framesize /= freqs[fr->sampling_frequency]<<(fr->lsf);
				fr->framesize = fr->framesize + fr->padding - 4;
			}
		break;
#endif 
		default:
			if(NOQUIET) error1("Layer type %i not supported in this build!", fr->lay); 

			return PARSE_BAD;
	}
	if (fr->framesize > MAXFRAMESIZE)
	{
		if(NOQUIET) error1("Frame size too big: %d", fr->framesize+4-fr->padding);

		return PARSE_BAD;
	}
	return PARSE_GOOD;
}

void set_pointer(mpg123_handle *fr, long backstep)
{
	fr->wordpointer = fr->bsbuf + fr->ssize - backstep;
	if (backstep)
	memcpy(fr->wordpointer,fr->bsbufold+fr->fsizeold-backstep,backstep);

	fr->bitindex = 0; 
}

/********************************/

double compute_bpf(mpg123_handle *fr)
{
	double bpf;

	switch(fr->lay) 
	{
		case 1:
			bpf = tabsel_123[fr->lsf][0][fr->bitrate_index];
			bpf *= 12000.0 * 4.0;
			bpf /= freqs[fr->sampling_frequency] <<(fr->lsf);
		break;
		case 2:
		case 3:
			bpf = tabsel_123[fr->lsf][fr->lay-1][fr->bitrate_index];
			bpf *= 144000;
			bpf /= freqs[fr->sampling_frequency] << (fr->lsf);
		break;
		default:
			bpf = 1.0;
	}

	return bpf;
}

int attribute_align_arg mpg123_spf(mpg123_handle *mh)
{
	if(mh == NULL) return MPG123_ERR;

	return mh->firsthead ? mh->spf : MPG123_ERR;
}

double attribute_align_arg mpg123_tpf(mpg123_handle *fr)
{
	static int bs[4] = { 0,384,1152,1152 };
	double tpf;
	if(fr == NULL || !fr->firsthead) return -1;

	tpf = (double) bs[fr->lay];
	tpf /= freqs[fr->sampling_frequency] << (fr->lsf);
	return tpf;
}

int attribute_align_arg mpg123_position(mpg123_handle *fr, off_t no, off_t buffsize,
	off_t  *current_frame,   off_t  *frames_left,
	double *current_seconds, double *seconds_left)
{
	double tpf;
	double dt = 0.0;
	off_t cur, left;
	double curs, lefts;

	if(!fr || !fr->rd) /* Isn't this too paranoid? */
	{
		debug("reader troubles!");
		return MPG123_ERR;
	}

	no += fr->num; /* no starts out as offset */
	cur = no;
	tpf = mpg123_tpf(fr);
	if(buffsize > 0 && fr->af.rate > 0 && fr->af.channels > 0)
	{
		dt = (double) buffsize / fr->af.rate / fr->af.channels;
		if(fr->af.encoding & MPG123_ENC_16) dt *= 0.5;
	}

	left = 0;

	if((fr->track_frames != 0) && (fr->track_frames >= fr->num)) left = no < fr->track_frames ? fr->track_frames - no : 0;
	else
	if(fr->rdat.filelen >= 0)
	{
		double bpf;
		off_t t = fr->rd->tell(fr);
		bpf = fr->mean_framesize ? fr->mean_framesize : compute_bpf(fr);
		left = (off_t)((double)(fr->rdat.filelen-t)/bpf);
		/* no can be different for prophetic purposes, file pointer is always associated with fr->num! */
		if(fr->num != no)
		{
			if(fr->num > no) left += fr->num - no;
			else
			{
				if(left >= (no - fr->num)) left -= no - fr->num;
				else left = 0; /* uh, oh! */
			}
		}
		/* I totally don't understand why we should re-estimate the given correct(?) value */
		/* fr->num = (unsigned long)((double)t/bpf); */
	}

	/* beginning with 0 or 1?*/
	curs = (double) no*tpf-dt;
	lefts = (double)left*tpf+dt;
#if 0
	curs = curs < 0 ? 0.0 : curs;
#endif
	if(left < 0 || lefts < 0)
	{ /* That is the case for non-seekable streams. */
		left  = 0;
		lefts = 0.0;
	}
	if(current_frame != NULL) *current_frame = cur;
	if(frames_left   != NULL) *frames_left   = left;
	if(current_seconds != NULL) *current_seconds = curs;
	if(seconds_left    != NULL) *seconds_left   = lefts;
	return MPG123_OK;
}

int get_songlen(mpg123_handle *fr,int no)
{
	double tpf;
	
	if(!fr)
		return 0;
	
	if(no < 0) {
		if(!fr->rd || fr->rdat.filelen < 0)
			return 0;
		no = (int) ((double) fr->rdat.filelen / compute_bpf(fr));
	}

	tpf = mpg123_tpf(fr);
	return (int) (no*tpf);
}

/* first attempt of read ahead check to find the real first header; cannot believe what junk is out there! */
static int do_readahead(mpg123_handle *fr, unsigned long newhead)
{
	unsigned long nexthead = 0;
	int hd = 0;
	off_t start, oret;
	int ret;

	if( ! (!fr->firsthead && fr->rdat.flags & (READER_SEEKABLE|READER_BUFFERED)) )
	return PARSE_GOOD;

	start = fr->rd->tell(fr);

	debug2("doing ahead check with BPF %d at %"OFF_P, fr->framesize+4, (off_p)start);
	/* step framesize bytes forward and read next possible header*/
	if((oret=fr->rd->skip_bytes(fr, fr->framesize))<0)
	{
		if(oret==READER_ERROR && NOQUIET) error("cannot seek!");

		return oret == MPG123_NEED_MORE ? PARSE_MORE : PARSE_ERR;
	}

	/* Read header, seek back. */
	hd = fr->rd->head_read(fr,&nexthead);
	if( fr->rd->back_bytes(fr, fr->rd->tell(fr)-start) < 0 )
	{
		if(NOQUIET) error("Cannot seek back!");

		return PARSE_ERR;
	}
	if(hd == MPG123_NEED_MORE) return PARSE_MORE;

	debug1("After fetching next header, at %"OFF_P, (off_p)fr->rd->tell(fr));
	if(!hd)
	{
		if(NOQUIET) warning("Cannot read next header, a one-frame stream? Duh...");
		return PARSE_END;
	}

	debug2("does next header 0x%08lx match first 0x%08lx?", nexthead, newhead);
	if(!head_check(nexthead) || !head_compatible(newhead, nexthead))
	{
		debug("No, the header was not valid, start from beginning...");
		fr->oldhead = 0; /* start over */
		/* try next byte for valid header */
		if((ret=fr->rd->back_bytes(fr, 3))<0)
		{
			if(NOQUIET) error("Cannot seek 3 bytes back!");

			return PARSE_ERR;
		}
		return PARSE_AGAIN;
	}
	else return PARSE_GOOD;
}

static int handle_id3v2(mpg123_handle *fr, unsigned long newhead)
{
	int ret;
	fr->oldhead = 0; /* Think about that. Used to be present only for skipping of junk, not resync-style wetwork. */
	ret = parse_new_id3(fr, newhead);
	if     (ret < 0) return ret;
#ifndef NO_ID3V2
	else if(ret > 0){ debug("got ID3v2"); fr->metaflags  |= MPG123_NEW_ID3|MPG123_ID3; }
	else debug("no useful ID3v2");
#endif
	return PARSE_AGAIN;
}

/* Advance a byte in stream to get next possible header and forget 
   buffered data if possible (for feed reader). */
#define FORGET_INTERVAL 1024 /* Used by callers to set forget flag each <n> bytes. */
static int forget_head_shift(mpg123_handle *fr, unsigned long *newheadp, int forget)
{
	int ret;
	if((ret=fr->rd->head_shift(fr,newheadp))<=0) return ret;
	/* Try to forget buffered data as early as possible to speed up parsing where
	   new data needs to be added for resync (and things would be re-parsed again
	   and again because of the start from beginning after hitting end). */
	if(forget && fr->rd->forget != NULL)
	{
		/* Ensure that the last 4 bytes stay in buffers for reading the header
		   anew. */
		if(!fr->rd->back_bytes(fr, 4))
		{
			fr->rd->forget(fr);
			fr->rd->back_bytes(fr, -4);
		}
	}
	return ret; /* No surprise here, error already triggered early return. */
}

/* watch out for junk/tags on beginning of stream by invalid header */
static int skip_junk(mpg123_handle *fr, unsigned long *newheadp, long *headcount)
{
	int ret;
	int freeformat_count = 0;
	long limit = 65536;
	unsigned long newhead = *newheadp;
	unsigned int forgetcount = 0;
	/* check for id3v2; first three bytes (of 4) are "ID3" */
	if((newhead & (unsigned long) 0xffffff00) == (unsigned long) 0x49443300)
	{
		return handle_id3v2(fr, newhead);
	}
	else if(VERBOSE2 && fr->silent_resync == 0) fprintf(stderr,"Note: Junk at the beginning (0x%08lx)\n",newhead);

	/* I even saw RIFF headers at the beginning of MPEG streams ;( */
	if(newhead == ('R'<<24)+('I'<<16)+('F'<<8)+'F')
	{
		if(VERBOSE2 && fr->silent_resync == 0) fprintf(stderr, "Note: Looks like a RIFF header.\n");

		if((ret=fr->rd->head_read(fr,&newhead))<=0) return ret;

		while(newhead != ('d'<<24)+('a'<<16)+('t'<<8)+'a')
		{
			if(++forgetcount > FORGET_INTERVAL) forgetcount = 0;
			if((ret=forget_head_shift(fr,&newhead,!forgetcount))<=0) return ret;
		}
		if((ret=fr->rd->head_read(fr,&newhead))<=0) return ret;

		if(VERBOSE2 && fr->silent_resync == 0) fprintf(stderr,"Note: Skipped RIFF header!\n");

		fr->oldhead = 0;
		*newheadp = newhead;
		return PARSE_AGAIN;
	}

	/*
		Unhandled junk... just continue search for a header, stepping in single bytes through next 64K.
		This is rather identical to the resync loop.
	*/
	debug("searching for header...");
	*newheadp = 0; /* Invalidate the external value. */
	ret = 0; /* We will check the value after the loop. */

	/* We prepare for at least the 64K bytes as usual, unless
	   user explicitly wanted more (even infinity). Never less. */
	if(fr->p.resync_limit < 0 || fr->p.resync_limit > limit)
	limit = fr->p.resync_limit;

	do
	{
		++(*headcount);
		if(limit >= 0 && *headcount >= limit) break;				

		if(++forgetcount > FORGET_INTERVAL) forgetcount = 0;
		if((ret=forget_head_shift(fr, &newhead, !forgetcount))<=0) return ret;

		if(head_check(newhead) && (ret=decode_header(fr, newhead, &freeformat_count))) break;
	} while(1);
	if(ret<0) return ret;

	if(limit >= 0 && *headcount >= limit)
	{
		if(NOQUIET) error1("Giving up searching valid MPEG header after %li bytes of junk.", *headcount);
		return PARSE_END;
	}
	else debug1("hopefully found one at %"OFF_P, (off_p)fr->rd->tell(fr));

	/* If the new header ist good, it is already decoded. */
	*newheadp = newhead;
	return PARSE_GOOD;
}

/* The newhead is bad, so let's check if it is something special, otherwise just resync. */
static int wetwork(mpg123_handle *fr, unsigned long *newheadp)
{
	int ret = PARSE_ERR;
	unsigned long newhead = *newheadp;
	*newheadp = 0;

	/* Classic ID3 tags. Read, then start parsing again. */
	if((newhead & 0xffffff00) == ('T'<<24)+('A'<<16)+('G'<<8))
	{
		fr->id3buf[0] = (unsigned char) ((newhead >> 24) & 0xff);
		fr->id3buf[1] = (unsigned char) ((newhead >> 16) & 0xff);
		fr->id3buf[2] = (unsigned char) ((newhead >> 8)  & 0xff);
		fr->id3buf[3] = (unsigned char) ( newhead        & 0xff);

		if((ret=fr->rd->fullread(fr,fr->id3buf+4,124)) < 0) return ret;

		fr->metaflags  |= MPG123_NEW_ID3|MPG123_ID3;
		fr->rdat.flags |= READER_ID3TAG; /* that marks id3v1 */
		if(VERBOSE3) fprintf(stderr,"Note: Skipped ID3v1 tag.\n");

		return PARSE_AGAIN;
	}
	/* This is similar to initial junk skipping code... */
	/* Check for id3v2; first three bytes (of 4) are "ID3" */
	if((newhead & (unsigned long) 0xffffff00) == (unsigned long) 0x49443300)
	{
		return handle_id3v2(fr, newhead);
	}
	else if(NOQUIET && fr->silent_resync == 0)
	{
		fprintf(stderr,"Note: Illegal Audio-MPEG-Header 0x%08lx at offset %"OFF_P".\n",
			newhead, (off_p)fr->rd->tell(fr)-4);
	}

	/* Now we got something bad at hand, try to recover. */

	if(NOQUIET && (newhead & 0xffffff00) == ('b'<<24)+('m'<<16)+('p'<<8)) fprintf(stderr,"Note: Could be a BMP album art.\n");

	if( !(fr->p.flags & MPG123_NO_RESYNC) )
	{
		long try = 0;
		long limit = fr->p.resync_limit;
		unsigned int forgetcount = 0;

		/* If a resync is needed the bitreservoir of previous frames is no longer valid */
		fr->bitreservoir = 0;

		if(NOQUIET && fr->silent_resync == 0) fprintf(stderr, "Note: Trying to resync...\n");

		do /* ... shift the header with additional single bytes until be found something that could be a header. */
		{
			++try;
			if(limit >= 0 && try >= limit) break;				

			if(++forgetcount > FORGET_INTERVAL) forgetcount = 0;
			if((ret=forget_head_shift(fr,&newhead,!forgetcount)) <= 0)
			{
				*newheadp = newhead;
				if(NOQUIET) fprintf (stderr, "Note: Hit end of (available) data during resync.\n");

				return ret ? ret : PARSE_END;
			}
			if(VERBOSE3) debug3("resync try %li at %"OFF_P", got newhead 0x%08lx", try, (off_p)fr->rd->tell(fr),  newhead);
		} while(!head_check(newhead));

		*newheadp = newhead;
		if(NOQUIET && fr->silent_resync == 0) fprintf (stderr, "Note: Skipped %li bytes in input.\n", try);

		/* Now we either got something that could be a header, or we gave up. */
		if(limit >= 0 && try >= limit)
		{
			if(NOQUIET)
			error1("Giving up resync after %li bytes - your stream is not nice... (maybe increasing resync limit could help).", try);

			fr->err = MPG123_RESYNC_FAIL;
			return PARSE_ERR;
		}
		else
		{
			debug1("Found possibly valid header 0x%lx... unsetting oldhead to reinit stream.", newhead);
			fr->oldhead = 0;
			return PARSE_RESYNC;
		}
	}
	else
	{
		if(NOQUIET) error("not attempting to resync...");

		fr->err = MPG123_OUT_OF_SYNC;
		return PARSE_ERR;
	}
	/* Control never goes here... we return before that. */
}
