ref: 686e2a5eb38b00b6eda2070228e42b7101ee2ce1
dir: /src/lzw/ftzopen.h/
/****************************************************************************
*
* ftzopen.h
*
* FreeType support for .Z compressed files.
*
* This optional component relies on NetBSD's zopen(). It should mainly
* be used to parse compressed PCF fonts, as found with many X11 server
* distributions.
*
* Copyright (C) 2005-2021 by
* David Turner.
*
* This file is part of the FreeType project, and may only be used,
* modified, and distributed under the terms of the FreeType project
* license, LICENSE.TXT. By continuing to use, modify, or distribute
* this file you indicate that you have read the license and
* understand and accept it fully.
*
*/
#ifndef FTZOPEN_H_
#define FTZOPEN_H_
#include <freetype/freetype.h>
FT_BEGIN_HEADER
/*
* This is a complete re-implementation of the LZW file reader,
* since the old one was incredibly badly written, using
* 400 KByte of heap memory before decompressing anything.
*
*/
#define FT_LZW_IN_BUFF_SIZE 64
#define FT_LZW_DEFAULT_STACK_SIZE 64
#define LZW_INIT_BITS 9
#define LZW_MAX_BITS 16
#define LZW_CLEAR 256
#define LZW_FIRST 257
#define LZW_BIT_MASK 0x1F
#define LZW_BLOCK_MASK 0x80
#define LZW_MASK( n ) ( ( 1U << (n) ) - 1U )
typedef enum FT_LzwPhase_
{
FT_LZW_PHASE_START = 0,
FT_LZW_PHASE_CODE,
FT_LZW_PHASE_STACK,
FT_LZW_PHASE_EOF
} FT_LzwPhase;
/*
* state of LZW decompressor
*
* small technical note
* --------------------
*
* We use a few tricks in this implementation that are explained here to
* ease debugging and maintenance.
*
* - First of all, the `prefix' and `suffix' arrays contain the suffix
* and prefix for codes over 256; this means that
*
* prefix_of(code) == state->prefix[code-256]
* suffix_of(code) == state->suffix[code-256]
*
* Each prefix is a 16-bit code, and each suffix an 8-bit byte.
*
* Both arrays are stored in a single memory block, pointed to by
* `state->prefix'. This means that the following equality is always
* true:
*
* state->suffix == (FT_Byte*)(state->prefix + state->prefix_size)
*
* Of course, state->prefix_size is the number of prefix/suffix slots
* in the arrays, corresponding to codes 256..255+prefix_size.
*
* - `free_ent' is the index of the next free entry in the `prefix'
* and `suffix' arrays. This means that the corresponding `next free
* code' is really `256+free_ent'.
*
* Moreover, `max_free' is the maximum value that `free_ent' can reach.
*
* `max_free' corresponds to `(1 << max_bits) - 256'. Note that this
* value is always <= 0xFF00, which means that both `free_ent' and
* `max_free' can be stored in an FT_UInt variable, even on 16-bit
* machines.
*
* If `free_ent == max_free', you cannot add new codes to the
* prefix/suffix table.
*
* - `num_bits' is the current number of code bits, starting at 9 and
* growing each time `free_ent' reaches the value of `free_bits'. The
* latter is computed as follows
*
* if num_bits < max_bits:
* free_bits = (1 << num_bits)-256
* else:
* free_bits = max_free + 1
*
* Since the value of `max_free + 1' can never be reached by
* `free_ent', `num_bits' cannot grow larger than `max_bits'.
*/
typedef struct FT_LzwStateRec_
{
FT_LzwPhase phase;
FT_Int in_eof;
FT_Byte buf_tab[16];
FT_UInt buf_offset;
FT_UInt buf_size;
FT_Bool buf_clear;
FT_Offset buf_total;
FT_UInt max_bits; /* max code bits, from file header */
FT_Int block_mode; /* block mode flag, from file header */
FT_UInt max_free; /* (1 << max_bits) - 256 */
FT_UInt num_bits; /* current code bit number */
FT_UInt free_ent; /* index of next free entry */
FT_UInt free_bits; /* if reached by free_ent, increment num_bits */
FT_UInt old_code;
FT_UInt old_char;
FT_UInt in_code;
FT_UShort* prefix; /* always dynamically allocated / reallocated */
FT_Byte* suffix; /* suffix = (FT_Byte*)(prefix + prefix_size) */
FT_UInt prefix_size; /* number of slots in `prefix' or `suffix' */
FT_Byte* stack; /* character stack */
FT_UInt stack_top;
FT_Offset stack_size;
FT_Byte stack_0[FT_LZW_DEFAULT_STACK_SIZE]; /* minimize heap alloc */
FT_Stream source; /* source stream */
FT_Memory memory;
} FT_LzwStateRec, *FT_LzwState;
FT_LOCAL( void )
ft_lzwstate_init( FT_LzwState state,
FT_Stream source );
FT_LOCAL( void )
ft_lzwstate_done( FT_LzwState state );
FT_LOCAL( void )
ft_lzwstate_reset( FT_LzwState state );
FT_LOCAL( FT_ULong )
ft_lzwstate_io( FT_LzwState state,
FT_Byte* buffer,
FT_ULong out_size );
/* */
FT_END_HEADER
#endif /* FTZOPEN_H_ */
/* END */