/src/freetype/src/lzw/ftzopen.h

  1/***************************************************************************/
  2/*                                                                         */
  3/*  ftzopen.h                                                              */
  4/*                                                                         */
  5/*    FreeType support for .Z compressed files.                            */
  6/*                                                                         */
  7/*  This optional component relies on NetBSD's zopen().  It should mainly  */
  8/*  be used to parse compressed PCF fonts, as found with many X11 server   */
  9/*  distributions.                                                         */
 10/*                                                                         */
 11/*  Copyright 2005, 2006, 2007, 2008 by David Turner.                      */
 12/*                                                                         */
 13/*  This file is part of the FreeType project, and may only be used,       */
 14/*  modified, and distributed under the terms of the FreeType project      */
 15/*  license, LICENSE.TXT.  By continuing to use, modify, or distribute     */
 16/*  this file you indicate that you have read the license and              */
 17/*  understand and accept it fully.                                        */
 18/*                                                                         */
 19/***************************************************************************/
 20
 21#ifndef __FT_ZOPEN_H__
 22#define __FT_ZOPEN_H__
 23
 24#include <ft2build.h>
 25#include FT_FREETYPE_H
 26
 27
 28  /*
 29   *  This is a complete re-implementation of the LZW file reader,
 30   *  since the old one was incredibly badly written, using
 31   *  400 KByte of heap memory before decompressing anything.
 32   *
 33   */
 34
 35#define FT_LZW_IN_BUFF_SIZE        64
 36#define FT_LZW_DEFAULT_STACK_SIZE  64
 37
 38#define LZW_INIT_BITS     9
 39#define LZW_MAX_BITS      16
 40
 41#define LZW_CLEAR         256
 42#define LZW_FIRST         257
 43
 44#define LZW_BIT_MASK      0x1f
 45#define LZW_BLOCK_MASK    0x80
 46#define LZW_MASK( n )     ( ( 1U << (n) ) - 1U )
 47
 48
 49  typedef enum  FT_LzwPhase_
 50  {
 51    FT_LZW_PHASE_START = 0,
 52    FT_LZW_PHASE_CODE,
 53    FT_LZW_PHASE_STACK,
 54    FT_LZW_PHASE_EOF
 55
 56  } FT_LzwPhase;
 57
 58
 59  /*
 60   *  state of LZW decompressor
 61   *
 62   *  small technical note
 63   *  --------------------
 64   *
 65   *  We use a few tricks in this implementation that are explained here to
 66   *  ease debugging and maintenance.
 67   *
 68   *  - First of all, the `prefix' and `suffix' arrays contain the suffix
 69   *    and prefix for codes over 256; this means that
 70   *
 71   *      prefix_of(code) == state->prefix[code-256]
 72   *      suffix_of(code) == state->suffix[code-256]
 73   *
 74   *    Each prefix is a 16-bit code, and each suffix an 8-bit byte.
 75   *
 76   *    Both arrays are stored in a single memory block, pointed to by
 77   *    `state->prefix'.  This means that the following equality is always
 78   *    true:
 79   *
 80   *      state->suffix == (FT_Byte*)(state->prefix + state->prefix_size)
 81   *
 82   *    Of course, state->prefix_size is the number of prefix/suffix slots
 83   *    in the arrays, corresponding to codes 256..255+prefix_size.
 84   *
 85   *  - `free_ent' is the index of the next free entry in the `prefix'
 86   *    and `suffix' arrays.  This means that the corresponding `next free
 87   *    code' is really `256+free_ent'.
 88   *
 89   *    Moreover, `max_free' is the maximum value that `free_ent' can reach.
 90   *
 91   *    `max_free' corresponds to `(1 << max_bits) - 256'.  Note that this
 92   *    value is always <= 0xFF00, which means that both `free_ent' and
 93   *    `max_free' can be stored in an FT_UInt variable, even on 16-bit
 94   *    machines.
 95   *
 96   *    If `free_ent == max_free', you cannot add new codes to the
 97   *    prefix/suffix table.
 98   *
 99   *  - `num_bits' is the current number of code bits, starting at 9 and
100   *    growing each time `free_ent' reaches the value of `free_bits'.  The
101   *    latter is computed as follows
102   *
103   *      if num_bits < max_bits:
104   *         free_bits = (1 << num_bits)-256
105   *      else:
106   *         free_bits = max_free + 1
107   *
108   *    Since the value of `max_free + 1' can never be reached by
109   *    `free_ent', `num_bits' cannot grow larger than `max_bits'.
110   */
111
112  typedef struct  FT_LzwStateRec_
113  {
114    FT_LzwPhase  phase;
115    FT_Int       in_eof;
116
117    FT_Byte      buf_tab[16];
118    FT_Int       buf_offset;
119    FT_Int       buf_size;
120    FT_Bool      buf_clear;
121    FT_Offset    buf_total;
122
123    FT_UInt      max_bits;    /* max code bits, from file header   */
124    FT_Int       block_mode;  /* block mode flag, from file header */
125    FT_UInt      max_free;    /* (1 << max_bits) - 256             */
126
127    FT_UInt      num_bits;    /* current code bit number */
128    FT_UInt      free_ent;    /* index of next free entry */
129    FT_UInt      free_bits;   /* if reached by free_ent, increment num_bits */
130    FT_UInt      old_code;
131    FT_UInt      old_char;
132    FT_UInt      in_code;
133
134    FT_UShort*   prefix;      /* always dynamically allocated / reallocated */
135    FT_Byte*     suffix;      /* suffix = (FT_Byte*)(prefix + prefix_size)  */
136    FT_UInt      prefix_size; /* number of slots in `prefix' or `suffix'    */
137
138    FT_Byte*     stack;       /* character stack */
139    FT_UInt      stack_top;
140    FT_Offset    stack_size;
141    FT_Byte      stack_0[FT_LZW_DEFAULT_STACK_SIZE]; /* minimize heap alloc */
142
143    FT_Stream    source;      /* source stream */
144    FT_Memory    memory;
145
146  } FT_LzwStateRec, *FT_LzwState;
147
148
149  FT_LOCAL( void )
150  ft_lzwstate_init( FT_LzwState  state,
151                    FT_Stream    source );
152
153  FT_LOCAL( void )
154  ft_lzwstate_done( FT_LzwState  state );
155
156
157  FT_LOCAL( void )
158  ft_lzwstate_reset( FT_LzwState  state );
159
160
161  FT_LOCAL( FT_ULong )
162  ft_lzwstate_io( FT_LzwState  state,
163                  FT_Byte*     buffer,
164                  FT_ULong     out_size );
165
166/* */
167
168#endif /* __FT_ZOPEN_H__ */
169
170
171/* END */