/*
 * jdhuff.c
 *
 * Copyright (C) 1991-1995, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains Huffman entropy decoding routines.
 *
 * Much of the complexity here has to do with supporting input suspension.
 * If the data source module demands suspension, we want to be able to back
 * up to the start of the current MCU.  To do this, we copy state variables
 * into local working storage, and update them back to the permanent
 * storage only upon successful completion of an MCU.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jdhuff.h"      /* Declarations shared with jdphuff.c */


/*
 * Expanded entropy decoder object for Huffman decoding.
 *
 * The savable_state subrecord contains fields that change within an MCU,
 * but must not be updated permanently until we complete the MCU.
 */

typedef struct {
	int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
} savable_state;

/* This macro is to work around compilers with missing or broken
 * structure assignment.  You'll need to fix this code if you have
 * such a compiler and you change MAX_COMPS_IN_SCAN.
 */

#ifndef NO_STRUCT_ASSIGN
#define ASSIGN_STATE( dest,src )  ( ( dest ) = ( src ) )
#else
#if MAX_COMPS_IN_SCAN == 4
#define ASSIGN_STATE( dest,src )  \
	( ( dest ).last_dc_val[0] = ( src ).last_dc_val[0],	\
	  ( dest ).last_dc_val[1] = ( src ).last_dc_val[1],	\
	  ( dest ).last_dc_val[2] = ( src ).last_dc_val[2],	\
	  ( dest ).last_dc_val[3] = ( src ).last_dc_val[3] )
#endif
#endif


typedef struct {
	struct jpeg_entropy_decoder pub; /* public fields */

	/* These fields are loaded into local variables at start of each MCU.
	 * In case of suspension, we exit WITHOUT updating them.
	 */
	bitread_perm_state bitstate; /* Bit buffer at start of MCU */
	savable_state saved;    /* Other state at start of MCU */

	/* These fields are NOT loaded into local working state. */
	unsigned int restarts_to_go; /* MCUs left in this restart interval */

	/* Pointers to derived tables (these workspaces have image lifespan) */
	d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
	d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
} huff_entropy_decoder;

typedef huff_entropy_decoder * huff_entropy_ptr;


/*
 * Initialize for a Huffman-compressed scan.
 */

METHODDEF void
start_pass_huff_decoder( j_decompress_ptr cinfo ) {
	huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
	int ci, dctbl, actbl;
	jpeg_component_info * compptr;

	/* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
	 * This ought to be an error condition, but we make it a warning because
	 * there are some baseline files out there with all zeroes in these bytes.
	 */
	if ( cinfo->Ss != 0 || cinfo->Se != DCTSIZE2 - 1 ||
		 cinfo->Ah != 0 || cinfo->Al != 0 ) {
		WARNMS( cinfo, JWRN_NOT_SEQUENTIAL );
	}

	for ( ci = 0; ci < cinfo->comps_in_scan; ci++ ) {
		compptr = cinfo->cur_comp_info[ci];
		dctbl = compptr->dc_tbl_no;
		actbl = compptr->ac_tbl_no;
		/* Make sure requested tables are present */
		if ( dctbl < 0 || dctbl >= NUM_HUFF_TBLS ||
			 cinfo->dc_huff_tbl_ptrs[dctbl] == NULL ) {
			ERREXIT1( cinfo, JERR_NO_HUFF_TABLE, dctbl );
		}
		if ( actbl < 0 || actbl >= NUM_HUFF_TBLS ||
			 cinfo->ac_huff_tbl_ptrs[actbl] == NULL ) {
			ERREXIT1( cinfo, JERR_NO_HUFF_TABLE, actbl );
		}
		/* Compute derived values for Huffman tables */
		/* We may do this more than once for a table, but it's not expensive */
		jpeg_make_d_derived_tbl( cinfo, cinfo->dc_huff_tbl_ptrs[dctbl],
								 &entropy->dc_derived_tbls[dctbl] );
		jpeg_make_d_derived_tbl( cinfo, cinfo->ac_huff_tbl_ptrs[actbl],
								 &entropy->ac_derived_tbls[actbl] );
		/* Initialize DC predictions to 0 */
		entropy->saved.last_dc_val[ci] = 0;
	}

	/* Initialize bitread state variables */
	entropy->bitstate.bits_left = 0;
	entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
	entropy->bitstate.printed_eod = FALSE;

	/* Initialize restart counter */
	entropy->restarts_to_go = cinfo->restart_interval;
}


/*
 * Compute the derived values for a Huffman table.
 * Note this is also used by jdphuff.c.
 */

GLOBAL void
jpeg_make_d_derived_tbl( j_decompress_ptr cinfo, JHUFF_TBL * htbl,
						 d_derived_tbl ** pdtbl ) {
	d_derived_tbl *dtbl;
	int p, i, l, si;
	int lookbits, ctr;
	char huffsize[257];
	unsigned int huffcode[257];
	unsigned int code;

	/* Allocate a workspace if we haven't already done so. */
	if ( *pdtbl == NULL ) {
		*pdtbl = ( d_derived_tbl * )
				 ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
											   SIZEOF( d_derived_tbl ) );
	}
	dtbl = *pdtbl;
	dtbl->pub = htbl;   /* fill in back link */

	/* Figure C.1: make table of Huffman code length for each symbol */
	/* Note that this is in code-length order. */

	p = 0;
	for ( l = 1; l <= 16; l++ ) {
		for ( i = 1; i <= (int) htbl->bits[l]; i++ )
			huffsize[p++] = (char) l;
	}
	huffsize[p] = 0;

	/* Figure C.2: generate the codes themselves */
	/* Note that this is in code-length order. */

	code = 0;
	si = huffsize[0];
	p = 0;
	while ( huffsize[p] ) {
		while ( ( (int) huffsize[p] ) == si ) {
			huffcode[p++] = code;
			code++;
		}
		code <<= 1;
		si++;
	}

	/* Figure F.15: generate decoding tables for bit-sequential decoding */

	p = 0;
	for ( l = 1; l <= 16; l++ ) {
		if ( htbl->bits[l] ) {
			dtbl->valptr[l] = p; /* huffval[] index of 1st symbol of code length l */
			dtbl->mincode[l] = huffcode[p]; /* minimum code of length l */
			p += htbl->bits[l];
			dtbl->maxcode[l] = huffcode[p - 1]; /* maximum code of length l */
		} else {
			dtbl->maxcode[l] = -1; /* -1 if no codes of this length */
		}
	}
	dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */

	/* Compute lookahead tables to speed up decoding.
	 * First we set all the table entries to 0, indicating "too long";
	 * then we iterate through the Huffman codes that are short enough and
	 * fill in all the entries that correspond to bit sequences starting
	 * with that code.
	 */

	MEMZERO( dtbl->look_nbits, SIZEOF( dtbl->look_nbits ) );

	p = 0;
	for ( l = 1; l <= HUFF_LOOKAHEAD; l++ ) {
		for ( i = 1; i <= (int) htbl->bits[l]; i++, p++ ) {
			/* l = current code's length, p = its index in huffcode[] & huffval[]. */
			/* Generate left-justified code followed by all possible bit sequences */
			lookbits = huffcode[p] << ( HUFF_LOOKAHEAD - l );
			for ( ctr = 1 << ( HUFF_LOOKAHEAD - l ); ctr > 0; ctr-- ) {
				dtbl->look_nbits[lookbits] = l;
				dtbl->look_sym[lookbits] = htbl->huffval[p];
				lookbits++;
			}
		}
	}
}


/*
 * Out-of-line code for bit fetching (shared with jdphuff.c).
 * See jdhuff.h for info about usage.
 * Note: current values of get_buffer and bits_left are passed as parameters,
 * but are returned in the corresponding fields of the state struct.
 *
 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
 * of get_buffer to be used.  (On machines with wider words, an even larger
 * buffer could be used.)  However, on some machines 32-bit shifts are
 * quite slow and take time proportional to the number of places shifted.
 * (This is true with most PC compilers, for instance.)  In this case it may
 * be a win to set MIN_GET_BITS to the minimum value of 15.  This reduces the
 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
 */

#ifdef SLOW_SHIFT_32
#define MIN_GET_BITS  15    /* minimum allowable value */
#else
#define MIN_GET_BITS  ( BIT_BUF_SIZE - 7 )
#endif


GLOBAL boolean
jpeg_fill_bit_buffer( bitread_working_state * state,
					  register bit_buf_type get_buffer, register int bits_left,
					  int nbits ) {
/* Load up the bit buffer to a depth of at least nbits */
/* Copy heavily used state fields into locals (hopefully registers) */
	register const JOCTET * next_input_byte = state->next_input_byte;
	register size_t bytes_in_buffer = state->bytes_in_buffer;
	register int c;

	/* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
	/* (It is assumed that no request will be for more than that many bits.) */

	while ( bits_left < MIN_GET_BITS ) {
		/* Attempt to read a byte */
		if ( state->unread_marker != 0 ) {
			goto no_more_data; /* can't advance past a marker */

		}
		if ( bytes_in_buffer == 0 ) {
			if ( !( *state->cinfo->src->fill_input_buffer )( state->cinfo ) ) {
				return FALSE;
			}
			next_input_byte = state->cinfo->src->next_input_byte;
			bytes_in_buffer = state->cinfo->src->bytes_in_buffer;
		}
		bytes_in_buffer--;
		c = GETJOCTET( *next_input_byte++ );

		/* If it's 0xFF, check and discard stuffed zero byte */
		if ( c == 0xFF ) {
			do {
				if ( bytes_in_buffer == 0 ) {
					if ( !( *state->cinfo->src->fill_input_buffer )( state->cinfo ) ) {
						return FALSE;
					}
					next_input_byte = state->cinfo->src->next_input_byte;
					bytes_in_buffer = state->cinfo->src->bytes_in_buffer;
				}
				bytes_in_buffer--;
				c = GETJOCTET( *next_input_byte++ );
			} while ( c == 0xFF );

			if ( c == 0 ) {
				/* Found FF/00, which represents an FF data byte */
				c = 0xFF;
			} else {
				/* Oops, it's actually a marker indicating end of compressed data. */
				/* Better put it back for use later */
				state->unread_marker = c;

no_more_data:
				/* There should be enough bits still left in the data segment; */
				/* if so, just break out of the outer while loop. */
				if ( bits_left >= nbits ) {
					break;
				}
				/* Uh-oh.  Report corrupted data to user and stuff zeroes into
				 * the data stream, so that we can produce some kind of image.
				 * Note that this code will be repeated for each byte demanded
				 * for the rest of the segment.  We use a nonvolatile flag to ensure
				 * that only one warning message appears.
				 */
				if ( !*( state->printed_eod_ptr ) ) {
					WARNMS( state->cinfo, JWRN_HIT_MARKER );
					*( state->printed_eod_ptr ) = TRUE;
				}
				c = 0; /* insert a zero byte into bit buffer */
			}
		}

		/* OK, load c into get_buffer */
		get_buffer = ( get_buffer << 8 ) | c;
		bits_left += 8;
	}

	/* Unload the local registers */
	state->next_input_byte = next_input_byte;
	state->bytes_in_buffer = bytes_in_buffer;
	state->get_buffer = get_buffer;
	state->bits_left = bits_left;

	return TRUE;
}


/*
 * Out-of-line code for Huffman code decoding.
 * See jdhuff.h for info about usage.
 */

GLOBAL int
jpeg_huff_decode( bitread_working_state * state,
				  register bit_buf_type get_buffer, register int bits_left,
				  d_derived_tbl * htbl, int min_bits ) {
	register int l = min_bits;
	register INT32 code;

	/* HUFF_DECODE has determined that the code is at least min_bits */
	/* bits long, so fetch that many bits in one swoop. */

	CHECK_BIT_BUFFER( *state, l, return -1 );
	code = GET_BITS( l );

	/* Collect the rest of the Huffman code one bit at a time. */
	/* This is per Figure F.16 in the JPEG spec. */

	while ( code > htbl->maxcode[l] ) {
		code <<= 1;
		CHECK_BIT_BUFFER( *state, 1, return -1 );
		code |= GET_BITS( 1 );
		l++;
	}

	/* Unload the local registers */
	state->get_buffer = get_buffer;
	state->bits_left = bits_left;

	/* With garbage input we may reach the sentinel value l = 17. */

	if ( l > 16 ) {
		WARNMS( state->cinfo, JWRN_HUFF_BAD_CODE );
		return 0;       /* fake a zero as the safest result */
	}

	return htbl->pub->huffval[ htbl->valptr[l] +
							   ( (int) ( code - htbl->mincode[l] ) ) ];
}


/*
 * Figure F.12: extend sign bit.
 * On some machines, a shift and add will be faster than a table lookup.
 */

#ifdef AVOID_TABLES

#define HUFF_EXTEND( x,s )  ( ( x ) < ( 1 << ( ( s ) - 1 ) ) ? ( x ) + ( ( ( -1 ) << ( s ) ) + 1 ) : ( x ) )

#else

#define HUFF_EXTEND( x,s )  ( ( x ) < extend_test[s] ? ( x ) + extend_offset[s] : ( x ) )

static const int extend_test[16] =   /* entry n is 2**(n-1) */
{ 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
  0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };

static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
{ 0, ( ( -1 ) << 1 ) + 1, ( ( -1 ) << 2 ) + 1, ( ( -1 ) << 3 ) + 1, ( ( -1 ) << 4 ) + 1,
  ( ( -1 ) << 5 ) + 1, ( ( -1 ) << 6 ) + 1, ( ( -1 ) << 7 ) + 1, ( ( -1 ) << 8 ) + 1,
  ( ( -1 ) << 9 ) + 1, ( ( -1 ) << 10 ) + 1, ( ( -1 ) << 11 ) + 1, ( ( -1 ) << 12 ) + 1,
  ( ( -1 ) << 13 ) + 1, ( ( -1 ) << 14 ) + 1, ( ( -1 ) << 15 ) + 1 };

#endif /* AVOID_TABLES */


/*
 * Check for a restart marker & resynchronize decoder.
 * Returns FALSE if must suspend.
 */

LOCAL boolean
process_restart( j_decompress_ptr cinfo ) {
	huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
	int ci;

	/* Throw away any unused bits remaining in bit buffer; */
	/* include any full bytes in next_marker's count of discarded bytes */
	cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
	entropy->bitstate.bits_left = 0;

	/* Advance past the RSTn marker */
	if ( !( *cinfo->marker->read_restart_marker )( cinfo ) ) {
		return FALSE;
	}

	/* Re-initialize DC predictions to 0 */
	for ( ci = 0; ci < cinfo->comps_in_scan; ci++ )
		entropy->saved.last_dc_val[ci] = 0;

	/* Reset restart counter */
	entropy->restarts_to_go = cinfo->restart_interval;

	/* Next segment can get another out-of-data warning */
	entropy->bitstate.printed_eod = FALSE;

	return TRUE;
}


/*
 * Decode and return one MCU's worth of Huffman-compressed coefficients.
 * The coefficients are reordered from zigzag order into natural array order,
 * but are not dequantized.
 *
 * The i'th block of the MCU is stored into the block pointed to by
 * MCU_data[i].  WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
 * (Wholesale zeroing is usually a little faster than retail...)
 *
 * Returns FALSE if data source requested suspension.  In that case no
 * changes have been made to permanent state.  (Exception: some output
 * coefficients may already have been assigned.  This is harmless for
 * this module, since we'll just re-assign them on the next call.)
 */

METHODDEF boolean
decode_mcu( j_decompress_ptr cinfo, JBLOCKROW *MCU_data ) {
	huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
	register int s, k, r;
	int blkn, ci;
	JBLOCKROW block;
	BITREAD_STATE_VARS;
	savable_state state;
	d_derived_tbl * dctbl;
	d_derived_tbl * actbl;
	jpeg_component_info * compptr;

	/* Process restart marker if needed; may have to suspend */
	if ( cinfo->restart_interval ) {
		if ( entropy->restarts_to_go == 0 ) {
			if ( !process_restart( cinfo ) ) {
				return FALSE;
			}
		}
	}

	/* Load up working state */
	BITREAD_LOAD_STATE( cinfo,entropy->bitstate );
	ASSIGN_STATE( state, entropy->saved );

	/* Outer loop handles each block in the MCU */

	for ( blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++ ) {
		block = MCU_data[blkn];
		ci = cinfo->MCU_membership[blkn];
		compptr = cinfo->cur_comp_info[ci];
		dctbl = entropy->dc_derived_tbls[compptr->dc_tbl_no];
		actbl = entropy->ac_derived_tbls[compptr->ac_tbl_no];

		/* Decode a single block's worth of coefficients */

		/* Section F.2.2.1: decode the DC coefficient difference */
		HUFF_DECODE( s, br_state, dctbl, return FALSE, label1 );
		if ( s ) {
			CHECK_BIT_BUFFER( br_state, s, return FALSE );
			r = GET_BITS( s );
			s = HUFF_EXTEND( r, s );
		}

		/* Shortcut if component's values are not interesting */
		if ( !compptr->component_needed ) {
			goto skip_ACs;
		}

		/* Convert DC difference to actual value, update last_dc_val */
		s += state.last_dc_val[ci];
		state.last_dc_val[ci] = s;
		/* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
		( *block )[0] = (JCOEF) s;

		/* Do we need to decode the AC coefficients for this component? */
		if ( compptr->DCT_scaled_size > 1 ) {

			/* Section F.2.2.2: decode the AC coefficients */
			/* Since zeroes are skipped, output area must be cleared beforehand */
			for ( k = 1; k < DCTSIZE2; k++ ) {
				HUFF_DECODE( s, br_state, actbl, return FALSE, label2 );

				r = s >> 4;
				s &= 15;

				if ( s ) {
					k += r;
					CHECK_BIT_BUFFER( br_state, s, return FALSE );
					r = GET_BITS( s );
					s = HUFF_EXTEND( r, s );
					/* Output coefficient in natural (dezigzagged) order.
					 * Note: the extra entries in jpeg_natural_order[] will save us
					 * if k >= DCTSIZE2, which could happen if the data is corrupted.
					 */
					( *block )[jpeg_natural_order[k]] = (JCOEF) s;
				} else {
					if ( r != 15 ) {
						break;
					}
					k += 15;
				}
			}

		} else {
skip_ACs:

			/* Section F.2.2.2: decode the AC coefficients */
			/* In this path we just discard the values */
			for ( k = 1; k < DCTSIZE2; k++ ) {
				HUFF_DECODE( s, br_state, actbl, return FALSE, label3 );

				r = s >> 4;
				s &= 15;

				if ( s ) {
					k += r;
					CHECK_BIT_BUFFER( br_state, s, return FALSE );
					DROP_BITS( s );
				} else {
					if ( r != 15 ) {
						break;
					}
					k += 15;
				}
			}

		}
	}

	/* Completed MCU, so update state */
	BITREAD_SAVE_STATE( cinfo,entropy->bitstate );
	ASSIGN_STATE( entropy->saved, state );

	/* Account for restart interval (no-op if not using restarts) */
	entropy->restarts_to_go--;

	return TRUE;
}


/*
 * Module initialization routine for Huffman entropy decoding.
 */

GLOBAL void
jinit_huff_decoder( j_decompress_ptr cinfo ) {
	huff_entropy_ptr entropy;
	int i;

	entropy = (huff_entropy_ptr)
				( *cinfo->mem->alloc_small ) ( (j_common_ptr) cinfo, JPOOL_IMAGE,
											   SIZEOF( huff_entropy_decoder ) );
	cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
	entropy->pub.start_pass = start_pass_huff_decoder;
	entropy->pub.decode_mcu = decode_mcu;

	/* Mark tables unallocated */
	for ( i = 0; i < NUM_HUFF_TBLS; i++ ) {
		entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
	}
}
