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  Every copy of AFPL Ghostscript must include a copy of the License, normally
  in a plain ASCII text file named PUBLIC.  The License grants you the right
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*/

/*$Id: shc.h,v 1.2 2000/09/19 19:00:50 lpd Exp $ */
/* Common definitions for filters using Huffman coding */

#ifndef shc_INCLUDED
#  define shc_INCLUDED

#include "gsbittab.h"
#include "scommon.h"

/*
 * These definitions are valid for code lengths up to 16 bits
 * and non-negative decoded values up to 15 bits.
 *
 * We define 3 different representations of the code: encoding tables,
 * decoding tables, and a definition table which can be generated easily
 * from frequency information and which in turn can easily generate
 * the encoding and decoding tables.
 *
 * The definition table has two parts: a list of the number of i-bit
 * codes for each i >= 1, and the decoded values corresponding to
 * the code values in increasing lexicographic order (which will also
 * normally be decreasing code frequency).  Calling these two lists
 * L[1..M] and V[0..N-1] respectively, we have the following invariants:
 *      - 1 <= M <= max_hc_length, N >= 2.
 *      - L[0] = 0.
 *      - for i=1..M, L[i] >= 0.
 *      - sum(i=1..M: L[i]) = N.
 *      - sum(i=1..M: L[i] * 2^-i) = 1.
 *      - V[0..N-1] are a permutation of the integers 0..N-1.
 */
#define max_hc_length 16
typedef struct hc_definition_s {
    ushort *counts;		/* [0..M] */
    uint num_counts;		/* M */
    ushort *values;		/* [0..N-1] */
    uint num_values;		/* N */
} hc_definition;

/* ------ Common state ------ */

/*
 * Define the common stream state for Huffman-coded filters.
 * Invariants when writing:
 *      0 <= bits_left <= hc_bits_size;
 *      Only the leftmost (hc_bits_size - bits_left) bits of bits
 *        contain valid data.
 */
#define stream_hc_state_common\
	stream_state_common;\
		/* The client sets the following before initialization. */\
	bool FirstBitLowOrder;\
		/* The following are updated dynamically. */\
	uint bits;		/* most recent bits of input or */\
				/* current bits of output */\
	int bits_left		/* # of valid low bits (input) or */\
				/* unused low bits (output) in above, */\
				/* 0 <= bits_left <= 7 */
typedef struct stream_hc_state_s {
    stream_hc_state_common;
} stream_hc_state;

#define hc_bits_size (arch_sizeof_int * 8)
#define s_hce_init_inline(ss)\
  ((ss)->bits = 0, (ss)->bits_left = hc_bits_size)
#define s_hcd_init_inline(ss)\
  ((ss)->bits = 0, (ss)->bits_left = 0)

/* ------ Encoding tables ------ */

/* Define the structure for the encoding tables. */
typedef struct hce_code_s {
    ushort code;
    ushort code_length;
} hce_code;

#define hce_entry(c, len) { c, len }

typedef struct hce_table_s {
    uint count;
    hce_code *codes;
} hce_table;

#define hce_bits_available(n)\
  (ss->bits_left >= (n) || wlimit - q > ((n) - ss->bits_left - 1) >> 3)

/* ------ Encoding utilities ------ */

/*
 * Put a code on the output.  The client is responsible for ensuring
 * that q does not exceed pw->limit.
 */

#ifdef DEBUG
#  define hc_print_value(code, clen)\
    (gs_debug_c('W') ?\
     (dlprintf2("[W]0x%x,%d\n", code, clen), 0) : 0)
#  define hc_print_value_then(code, clen) hc_print_value(code, clen),
#else
#  define hc_print_value(code, clen) 0
#  define hc_print_value_then(code, clen)	/* */
#endif
#define hc_print_code(rp) hc_print_value((rp)->code, (rp)->code_length)

/* Declare variables that hold the encoder state. */
#define hce_declare_state\
	register uint bits;\
	register int bits_left

/* Load the state from the stream. */
/* Free variables: ss, bits, bits_left. */
#define hce_load_state()\
	bits = ss->bits, bits_left = ss->bits_left

/* Store the state back in the stream. */
/* Free variables: ss, bits, bits_left. */
#define hce_store_state()\
	ss->bits = bits, ss->bits_left = bits_left

/* Put a code on the stream. */
void hc_put_code_proc(P3(bool, byte *, uint));

#define hc_put_value(ss, q, code, clen)\
  (hc_print_value_then(code, clen)\
   ((bits_left -= (clen)) >= 0 ?\
    (bits += (code) << bits_left) :\
    (hc_put_code_proc((ss)->FirstBitLowOrder,\
		      q += hc_bits_size >> 3,\
		      (bits + ((code) >> -bits_left))),\
     bits = (code) << (bits_left += hc_bits_size))))
#define hc_put_code(ss, q, cp)\
  hc_put_value(ss, q, (cp)->code, (cp)->code_length)

/*
 * Force out the final bits to the output.
 * Note that this does a store_state, but not a load_state.
 */
byte *hc_put_last_bits_proc(P4(stream_hc_state *, byte *, uint, int));

#define hc_put_last_bits(ss, q)\
  hc_put_last_bits_proc(ss, q, bits, bits_left)

/* ------ Decoding tables ------ */

/*
 * Define the structure for the decoding tables.
 * First-level nodes are either leaves, which have
 *      value = decoded value
 *      code_length <= initial_bits
 * or non-leaves, which have
 *      value = the index of a sub-table
 *      code_length = initial_bits + the number of additional dispatch bits
 * Second-level nodes are always leaves, with
 *      code_length = the actual number of bits in the code - initial_bits.
 */

typedef struct hcd_code_s {
    short value;
    ushort code_length;
} hcd_code;

typedef struct hcd_table_s {
    uint count;
    uint initial_bits;
    hcd_code *codes;
} hcd_table;

/* Declare variables that hold the decoder state. */
#define hcd_declare_state\
	register const byte *p;\
	const byte *rlimit;\
	uint bits;\
	int bits_left

/* Load the state from the stream. */
/* Free variables: pr, ss, p, rlimit, bits, bits_left. */
#define hcd_load_state()\
	p = pr->ptr,\
	rlimit = pr->limit,\
	bits = ss->bits,\
	bits_left = ss->bits_left

/* Store the state back in the stream. */
/* Put back any complete bytes into the input buffer. */
/* Free variables: pr, ss, p, bits, bits_left. */
#define hcd_store_state()\
	pr->ptr = p -= (bits_left >> 3),\
	ss->bits = bits >>= (bits_left & ~7),\
	ss->bits_left = bits_left &= 7

/* Macros to get blocks of bits from the input stream. */
/* Invariants: 0 <= bits_left <= bits_size; */
/* bits [bits_left-1..0] contain valid data. */

#define hcd_bits_available(n)\
  (bits_left >= (n) || rlimit - p > ((n) - bits_left - 1) >> 3)
/* For hcd_ensure_bits, n must not be greater than 8. */
#define HCD_ENSURE_BITS_ELSE(n)\
  if (bits_left >= n)\
    DO_NOTHING;\
  else HCD_MORE_BITS_ELSE
#define hcd_ensure_bits(n, outl)\
  BEGIN HCD_ENSURE_BITS_ELSE(n) goto outl; END

/* Load more bits into the buffer. */
#define HCD_MORE_BITS_1_ELSE\
  if (p < rlimit) {\
    int c = *++p;\
\
    if (ss->FirstBitLowOrder)\
      c = byte_reverse_bits[c];\
    bits = (bits << 8) + c, bits_left += 8;\
  } else
#if hc_bits_size == 16
#  define HCD_MORE_BITS_ELSE HCD_MORE_BITS_1_ELSE
#else /* hc_bits_size >= 32 */
#  define HCD_MORE_BITS_ELSE\
  if (rlimit - p >= 3) {\
    if (ss->FirstBitLowOrder)\
      bits = (bits << 24) + ((uint)byte_reverse_bits[p[1]] << 16) + ((uint)byte_reverse_bits[p[2]] << 8) + byte_reverse_bits[p[3]];\
    else\
      bits = (bits << 24) + ((uint)p[1] << 16) + ((uint)p[2] << 8) + p[3];\
    bits_left += 24, p += 3;\
  } else HCD_MORE_BITS_1_ELSE
#endif
#define hcd_more_bits(outl)\
  BEGIN HCD_MORE_BITS_ELSE goto outl; END

#define hcd_peek_bits(n) ((bits >> (bits_left - (n))) & ((1 << (n)) - 1))

/* hcd_peek_var_bits requires bits_left <= 8. */
#define hcd_peek_var_bits(n)\
  ((bits >> (bits_left - (n))) & byte_right_mask[n])

/* hcd_peek_bits_left requires bits_left <= 8. */
#define hcd_peek_bits_left()\
  (bits & byte_right_mask[bits_left])

#define hcd_skip_bits(n) (bits_left -= (n))

#endif /* shc_INCLUDED */
