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 (C) 2005-2023 by
12 * David Turner.
13 *
14 * This file is part of the FreeType project, and may only be used,
15 * modified, and distributed under the terms of the FreeType project
16 * license, LICENSE.TXT. By continuing to use, modify, or distribute
17 * this file you indicate that you have read the license and
18 * understand and accept it fully.
19 *
20 */
21
22 #ifndef FTZOPEN_H_
23 #define FTZOPEN_H_
24
25 #include <freetype/freetype.h>
26
27 FT_BEGIN_HEADER
28
29 /*
30 * This is a complete re-implementation of the LZW file reader,
31 * since the old one was incredibly badly written, using
32 * 400 KByte of heap memory before decompressing anything.
33 *
34 */
35
36 #define FT_LZW_IN_BUFF_SIZE 64
37 #define FT_LZW_DEFAULT_STACK_SIZE 64
38
39 #define LZW_INIT_BITS 9
40 #define LZW_MAX_BITS 16
41
42 #define LZW_CLEAR 256
43 #define LZW_FIRST 257
44
45 #define LZW_BIT_MASK 0x1F
46 #define LZW_BLOCK_MASK 0x80
47 #define LZW_MASK( n ) ( ( 1U << (n) ) - 1U )
48
49
50 typedef enum FT_LzwPhase_
51 {
52 FT_LZW_PHASE_START = 0,
53 FT_LZW_PHASE_CODE,
54 FT_LZW_PHASE_STACK,
55 FT_LZW_PHASE_EOF
56
57 } FT_LzwPhase;
58
59
60 /*
61 * state of LZW decompressor
62 *
63 * small technical note
64 * --------------------
65 *
66 * We use a few tricks in this implementation that are explained here to
67 * ease debugging and maintenance.
68 *
69 * - First of all, the `prefix' and `suffix' arrays contain the suffix
70 * and prefix for codes over 256; this means that
71 *
72 * prefix_of(code) == state->prefix[code-256]
73 * suffix_of(code) == state->suffix[code-256]
74 *
75 * Each prefix is a 16-bit code, and each suffix an 8-bit byte.
76 *
77 * Both arrays are stored in a single memory block, pointed to by
78 * `state->prefix'. This means that the following equality is always
79 * true:
80 *
81 * state->suffix == (FT_Byte*)(state->prefix + state->prefix_size)
82 *
83 * Of course, state->prefix_size is the number of prefix/suffix slots
84 * in the arrays, corresponding to codes 256..255+prefix_size.
85 *
86 * - `free_ent' is the index of the next free entry in the `prefix'
87 * and `suffix' arrays. This means that the corresponding `next free
88 * code' is really `256+free_ent'.
89 *
90 * Moreover, `max_free' is the maximum value that `free_ent' can reach.
91 *
92 * `max_free' corresponds to `(1 << max_bits) - 256'. Note that this
93 * value is always <= 0xFF00, which means that both `free_ent' and
94 * `max_free' can be stored in an FT_UInt variable, even on 16-bit
95 * machines.
96 *
97 * If `free_ent == max_free', you cannot add new codes to the
98 * prefix/suffix table.
99 *
100 * - `num_bits' is the current number of code bits, starting at 9 and
101 * growing each time `free_ent' reaches the value of `free_bits'. The
102 * latter is computed as follows
103 *
104 * if num_bits < max_bits:
105 * free_bits = (1 << num_bits)-256
106 * else:
107 * free_bits = max_free + 1
108 *
109 * Since the value of `max_free + 1' can never be reached by
110 * `free_ent', `num_bits' cannot grow larger than `max_bits'.
111 */
112
113 typedef struct FT_LzwStateRec_
114 {
115 FT_LzwPhase phase;
116 FT_Int in_eof;
117
118 FT_Byte buf_tab[16];
119 FT_UInt buf_offset;
120 FT_UInt buf_size;
121 FT_Bool buf_clear;
122 FT_Offset buf_total;
123
124 FT_UInt max_bits; /* max code bits, from file header */
125 FT_Int block_mode; /* block mode flag, from file header */
126 FT_UInt max_free; /* (1 << max_bits) - 256 */
127
128 FT_UInt num_bits; /* current code bit number */
129 FT_UInt free_ent; /* index of next free entry */
130 FT_UInt free_bits; /* if reached by free_ent, increment num_bits */
131 FT_UInt old_code;
132 FT_UInt old_char;
133 FT_UInt in_code;
134
135 FT_UShort* prefix; /* always dynamically allocated / reallocated */
136 FT_Byte* suffix; /* suffix = (FT_Byte*)(prefix + prefix_size) */
137 FT_UInt prefix_size; /* number of slots in `prefix' or `suffix' */
138
139 FT_Byte* stack; /* character stack */
140 FT_UInt stack_top;
141 FT_Offset stack_size;
142 FT_Byte stack_0[FT_LZW_DEFAULT_STACK_SIZE]; /* minimize heap alloc */
143
144 FT_Stream source; /* source stream */
145 FT_Memory memory;
146
147 } FT_LzwStateRec, *FT_LzwState;
148
149
150 FT_LOCAL( void )
151 ft_lzwstate_init( FT_LzwState state,
152 FT_Stream source );
153
154 FT_LOCAL( void )
155 ft_lzwstate_done( FT_LzwState state );
156
157
158 FT_LOCAL( void )
159 ft_lzwstate_reset( FT_LzwState state );
160
161
162 FT_LOCAL( FT_ULong )
163 ft_lzwstate_io( FT_LzwState state,
164 FT_Byte* buffer,
165 FT_ULong out_size );
166
167 /* */
168
169 FT_END_HEADER
170
171 #endif /* FTZOPEN_H_ */
172
173
174 /* END */