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DobieStation/ext/libdeflate/lib/deflate_decompress.c
a dinosaur a491dce51a CISO reading support (#123) 
This changes up the build system quite a bit.
2019-02-25 18:51:46 -05:00

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/*
* deflate_decompress.c - a decompressor for DEFLATE
*
* Copyright 2016 Eric Biggers
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use,
* copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following
* conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*
* ---------------------------------------------------------------------------
*
* This is a highly optimized DEFLATE decompressor. When compiled with gcc on
* x86_64, it decompresses data in about 52% of the time of zlib (48% if BMI2
* instructions are available). On other architectures it should still be
* significantly faster than zlib, but the difference may be smaller.
*
* Why this is faster than zlib's implementation:
*
* - Word accesses rather than byte accesses when reading input
* - Word accesses rather than byte accesses when copying matches
* - Faster Huffman decoding combined with various DEFLATE-specific tricks
* - Larger bitbuffer variable that doesn't need to be filled as often
* - Other optimizations to remove unnecessary branches
* - Only full-buffer decompression is supported, so the code doesn't need to
* support stopping and resuming decompression.
* - On x86_64, compile a version of the decompression routine using BMI2
* instructions and use it automatically at runtime when supported.
*/
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include "deflate_constants.h"
#include "unaligned.h"
#include "libdeflate.h"
/*
* If the expression passed to SAFETY_CHECK() evaluates to false, then the
* decompression routine immediately returns LIBDEFLATE_BAD_DATA, indicating the
* compressed data is invalid.
*
* Theoretically, these checks could be disabled for specialized applications
* where all input to the decompressor will be trusted.
*/
#if 0
# pragma message("UNSAFE DECOMPRESSION IS ENABLED. THIS MUST ONLY BE USED IF THE DECOMPRESSOR INPUT WILL ALWAYS BE TRUSTED!")
# define SAFETY_CHECK(expr) (void)(expr)
#else
# define SAFETY_CHECK(expr) if (unlikely(!(expr))) return LIBDEFLATE_BAD_DATA
#endif
/*
* Each TABLEBITS number is the base-2 logarithm of the number of entries in the
* main portion of the corresponding decode table. Each number should be large
* enough to ensure that for typical data, the vast majority of symbols can be
* decoded by a direct lookup of the next TABLEBITS bits of compressed data.
* However, this must be balanced against the fact that a larger table requires
* more memory and requires more time to fill.
*
* Note: you cannot change a TABLEBITS number without also changing the
* corresponding ENOUGH number!
*/
#define PRECODE_TABLEBITS 7
#define LITLEN_TABLEBITS 10
#define OFFSET_TABLEBITS 8
/*
* Each ENOUGH number is the maximum number of decode table entries that may be
* required for the corresponding Huffman code, including the main table and all
* subtables. Each number depends on three parameters:
*
* (1) the maximum number of symbols in the code (DEFLATE_NUM_*_SYMS)
* (2) the number of main table bits (the TABLEBITS numbers defined above)
* (3) the maximum allowed codeword length (DEFLATE_MAX_*_CODEWORD_LEN)
*
* The ENOUGH numbers were computed using the utility program 'enough' from
* zlib. This program enumerates all possible relevant Huffman codes to find
* the worst-case usage of decode table entries.
*/
#define PRECODE_ENOUGH 128 /* enough 19 7 7 */
#define LITLEN_ENOUGH 1334 /* enough 288 10 15 */
#define OFFSET_ENOUGH 402 /* enough 32 8 15 */
/*
* Type for codeword lengths.
*/
typedef u8 len_t;
/*
* The main DEFLATE decompressor structure. Since this implementation only
* supports full buffer decompression, this structure does not store the entire
* decompression state, but rather only some arrays that are too large to
* comfortably allocate on the stack.
*/
struct libdeflate_decompressor {
/*
* The arrays aren't all needed at the same time. 'precode_lens' and
* 'precode_decode_table' are unneeded after 'lens' has been filled.
* Furthermore, 'lens' need not be retained after building the litlen
* and offset decode tables. In fact, 'lens' can be in union with
* 'litlen_decode_table' provided that 'offset_decode_table' is separate
* and is built first.
*/
union {
len_t precode_lens[DEFLATE_NUM_PRECODE_SYMS];
struct {
len_t lens[DEFLATE_NUM_LITLEN_SYMS +
DEFLATE_NUM_OFFSET_SYMS +
DEFLATE_MAX_LENS_OVERRUN];
u32 precode_decode_table[PRECODE_ENOUGH];
} l;
u32 litlen_decode_table[LITLEN_ENOUGH];
} u;
u32 offset_decode_table[OFFSET_ENOUGH];
/* used only during build_decode_table() */
u16 sorted_syms[DEFLATE_MAX_NUM_SYMS];
bool static_codes_loaded;
};
/*****************************************************************************
* Input bitstream *
*****************************************************************************/
/*
* The state of the "input bitstream" consists of the following variables:
*
* - in_next: pointer to the next unread byte in the input buffer
*
* - in_end: pointer just past the end of the input buffer
*
* - bitbuf: a word-sized variable containing bits that have been read from
* the input buffer. The buffered bits are right-aligned
* (they're the low-order bits).
*
* - bitsleft: number of bits in 'bitbuf' that are valid.
*
* To make it easier for the compiler to optimize the code by keeping variables
* in registers, these are declared as normal variables and manipulated using
* macros.
*/
/*
* The type for the bitbuffer variable ('bitbuf' described above). For best
* performance, this should have size equal to a machine word.
*
* 64-bit platforms have a significant advantage: they get a bigger bitbuffer
* which they have to fill less often.
*/
typedef machine_word_t bitbuf_t;
/*
* Number of bits the bitbuffer variable can hold.
*
* This is one less than the obvious value because of the optimized arithmetic
* in FILL_BITS_WORDWISE() that leaves 'bitsleft' in the range
* [WORDBITS - 8, WORDBITS - 1] rather than [WORDBITS - 7, WORDBITS].
*/
#define BITBUF_NBITS (8 * sizeof(bitbuf_t) - 1)
/*
* The maximum number of bits that can be ensured in the bitbuffer variable,
* i.e. the maximum value of 'n' that can be passed ENSURE_BITS(n). The decoder
* only reads whole bytes from memory, so this is the lowest value of 'bitsleft'
* at which another byte cannot be read without first consuming some bits.
*/
#define MAX_ENSURE (BITBUF_NBITS - 7)
/*
* Evaluates to true if 'n' is a valid argument to ENSURE_BITS(n), or false if
* 'n' is too large to be passed to ENSURE_BITS(n). Note: if 'n' is a compile
* time constant, then this expression will be a compile-type constant.
* Therefore, CAN_ENSURE() can be used choose between alternative
* implementations at compile time.
*/
#define CAN_ENSURE(n) ((n) <= MAX_ENSURE)
/*
* Fill the bitbuffer variable, reading one byte at a time.
*
* If we would overread the input buffer, we just don't read anything, leaving
* the bits zeroed but marking them filled. This simplifies the decompressor
* because it removes the need to distinguish between real overreads and
* overreads that occur only because of the decompressor's own lookahead.
*
* The disadvantage is that real overreads are not detected immediately.
* However, this is safe because the decompressor is still guaranteed to make
* forward progress when presented never-ending 0 bits. In an existing block
* output will be getting generated, whereas new blocks can only be uncompressed
* (since the type code for uncompressed blocks is 0), for which we check for
* previous overread. But even if we didn't check, uncompressed blocks would
* fail to validate because LEN would not equal ~NLEN. So the decompressor will
* eventually either detect that the output buffer is full, or detect invalid
* input, or finish the final block.
*/
#define FILL_BITS_BYTEWISE() \
do { \
if (likely(in_next != in_end)) \
bitbuf |= (bitbuf_t)*in_next++ << bitsleft; \
else \
overrun_count++; \
bitsleft += 8; \
} while (bitsleft <= BITBUF_NBITS - 8)
/*
* Fill the bitbuffer variable by reading the next word from the input buffer
* and branchlessly updating 'in_next' and 'bitsleft' based on how many bits
* were filled. This can be significantly faster than FILL_BITS_BYTEWISE().
* However, for this to work correctly, the word must be interpreted in
* little-endian format. In addition, the memory access may be unaligned.
* Therefore, this method is most efficient on little-endian architectures that
* support fast unaligned access, such as x86 and x86_64.
*
* For faster updating of 'bitsleft', we consider the bitbuffer size in bits to
* be 1 less than the word size and therefore be all 1 bits. Then the number of
* bits filled is the value of the 0 bits in position >= 3 when changed to 1.
* E.g. if words are 64 bits and bitsleft = 16 = b010000 then we refill b101000
* = 40 bits = 5 bytes. This uses only 4 operations to update 'in_next' and
* 'bitsleft': one each of +, ^, >>, and |. (Not counting operations the
* compiler optimizes out.) In contrast, the alternative of:
*
* in_next += (BITBUF_NBITS - bitsleft) >> 3;
* bitsleft += (BITBUF_NBITS - bitsleft) & ~7;
*
* (where BITBUF_NBITS would be WORDBITS rather than WORDBITS - 1) would on
* average refill an extra bit, but uses 5 operations: two +, and one each of
* -, >>, and &. Also the - and & must be completed before 'bitsleft' can be
* updated, while the current solution updates 'bitsleft' with no dependencies.
*/
#define FILL_BITS_WORDWISE() \
do { \
/* BITBUF_NBITS must be all 1's in binary, see above */ \
STATIC_ASSERT((BITBUF_NBITS & (BITBUF_NBITS + 1)) == 0);\
\
bitbuf |= get_unaligned_leword(in_next) << bitsleft; \
in_next += (bitsleft ^ BITBUF_NBITS) >> 3; \
bitsleft |= BITBUF_NBITS & ~7; \
} while (0)
/*
* Does the bitbuffer variable currently contain at least 'n' bits?
*/
#define HAVE_BITS(n) (bitsleft >= (n))
/*
* Load more bits from the input buffer until the specified number of bits is
* present in the bitbuffer variable. 'n' cannot be too large; see MAX_ENSURE
* and CAN_ENSURE().
*/
#define ENSURE_BITS(n) \
if (!HAVE_BITS(n)) { \
if (CPU_IS_LITTLE_ENDIAN() && \
UNALIGNED_ACCESS_IS_FAST && \
likely(in_end - in_next >= sizeof(bitbuf_t))) \
FILL_BITS_WORDWISE(); \
else \
FILL_BITS_BYTEWISE(); \
}
/*
* Return the next 'n' bits from the bitbuffer variable without removing them.
*/
#define BITS(n) ((u32)bitbuf & (((u32)1 << (n)) - 1))
/*
* Remove the next 'n' bits from the bitbuffer variable.
*/
#define REMOVE_BITS(n) (bitbuf >>= (n), bitsleft -= (n))
/*
* Remove and return the next 'n' bits from the bitbuffer variable.
*/
#define POP_BITS(n) (tmp32 = BITS(n), REMOVE_BITS(n), tmp32)
/*
* Verify that the input buffer hasn't been overread, then align the input to
* the next byte boundary, discarding any remaining bits in the current byte.
*
* Note that if the bitbuffer variable currently contains more than 7 bits, then
* we must rewind 'in_next', effectively putting those bits back. Only the bits
* in what would be the "current" byte if we were reading one byte at a time can
* be actually discarded.
*/
#define ALIGN_INPUT() \
do { \
SAFETY_CHECK(overrun_count <= (bitsleft >> 3)); \
in_next -= (bitsleft >> 3) - overrun_count; \
overrun_count = 0; \
bitbuf = 0; \
bitsleft = 0; \
} while(0)
/*
* Read a 16-bit value from the input. This must have been preceded by a call
* to ALIGN_INPUT(), and the caller must have already checked for overrun.
*/
#define READ_U16() (tmp16 = get_unaligned_le16(in_next), in_next += 2, tmp16)
/*****************************************************************************
* Huffman decoding *
*****************************************************************************/
/*
* A decode table for order TABLEBITS consists of a main table of (1 <<
* TABLEBITS) entries followed by a variable number of subtables.
*
* The decoding algorithm takes the next TABLEBITS bits of compressed data and
* uses them as an index into the decode table. The resulting entry is either a
* "direct entry", meaning that it contains the value desired, or a "subtable
* pointer", meaning that the entry references a subtable that must be indexed
* using more bits of the compressed data to decode the symbol.
*
* Each decode table (a main table along with with its subtables, if any) is
* associated with a Huffman code. Logically, the result of a decode table
* lookup is a symbol from the alphabet from which the corresponding Huffman
* code was constructed. A symbol with codeword length n <= TABLEBITS is
* associated with 2**(TABLEBITS - n) direct entries in the table, whereas a
* symbol with codeword length n > TABLEBITS is associated with one or more
* subtable entries.
*
* On top of this basic design, we implement several optimizations:
*
* - We store the length of each codeword directly in each of its decode table
* entries. This allows the codeword length to be produced without indexing
* an additional table.
*
* - When beneficial, we don't store the Huffman symbol itself, but instead data
* generated from it. For example, when decoding an offset symbol in DEFLATE,
* it's more efficient if we can decode the offset base and number of extra
* offset bits directly rather than decoding the offset symbol and then
* looking up both of those values in an additional table or tables.
*
* The size of each decode table entry is 32 bits, which provides slightly
* better performance than 16-bit entries on 32 and 64 bit processers, provided
* that the table doesn't get so large that it takes up too much memory and
* starts generating cache misses. The bits of each decode table entry are
* defined as follows:
*
* - Bits 30 -- 31: flags (see below)
* - Bits 8 -- 29: decode result: a Huffman symbol or related data
* - Bits 0 -- 7: codeword length
*/
/*
* This flag is set in all main decode table entries that represent subtable
* pointers.
*/
#define HUFFDEC_SUBTABLE_POINTER 0x80000000
/*
* This flag is set in all entries in the litlen decode table that represent
* literals.
*/
#define HUFFDEC_LITERAL 0x40000000
/* Mask for extracting the codeword length from a decode table entry. */
#define HUFFDEC_LENGTH_MASK 0xFF
/* Shift to extract the decode result from a decode table entry. */
#define HUFFDEC_RESULT_SHIFT 8
/* Shift a decode result into its position in the decode table entry. */
#define HUFFDEC_RESULT_ENTRY(result) ((u32)(result) << HUFFDEC_RESULT_SHIFT)
/* The decode result for each precode symbol. There is no special optimization
* for the precode; the decode result is simply the symbol value. */
static const u32 precode_decode_results[DEFLATE_NUM_PRECODE_SYMS] = {
#define ENTRY(presym) HUFFDEC_RESULT_ENTRY(presym)
ENTRY(0) , ENTRY(1) , ENTRY(2) , ENTRY(3) ,
ENTRY(4) , ENTRY(5) , ENTRY(6) , ENTRY(7) ,
ENTRY(8) , ENTRY(9) , ENTRY(10) , ENTRY(11) ,
ENTRY(12) , ENTRY(13) , ENTRY(14) , ENTRY(15) ,
ENTRY(16) , ENTRY(17) , ENTRY(18) ,
#undef ENTRY
};
/* The decode result for each litlen symbol. For literals, this is the literal
* value itself and the HUFFDEC_LITERAL flag. For lengths, this is the length
* base and the number of extra length bits. */
static const u32 litlen_decode_results[DEFLATE_NUM_LITLEN_SYMS] = {
/* Literals */
#define ENTRY(literal) (HUFFDEC_LITERAL | HUFFDEC_RESULT_ENTRY(literal))
ENTRY(0) , ENTRY(1) , ENTRY(2) , ENTRY(3) ,
ENTRY(4) , ENTRY(5) , ENTRY(6) , ENTRY(7) ,
ENTRY(8) , ENTRY(9) , ENTRY(10) , ENTRY(11) ,
ENTRY(12) , ENTRY(13) , ENTRY(14) , ENTRY(15) ,
ENTRY(16) , ENTRY(17) , ENTRY(18) , ENTRY(19) ,
ENTRY(20) , ENTRY(21) , ENTRY(22) , ENTRY(23) ,
ENTRY(24) , ENTRY(25) , ENTRY(26) , ENTRY(27) ,
ENTRY(28) , ENTRY(29) , ENTRY(30) , ENTRY(31) ,
ENTRY(32) , ENTRY(33) , ENTRY(34) , ENTRY(35) ,
ENTRY(36) , ENTRY(37) , ENTRY(38) , ENTRY(39) ,
ENTRY(40) , ENTRY(41) , ENTRY(42) , ENTRY(43) ,
ENTRY(44) , ENTRY(45) , ENTRY(46) , ENTRY(47) ,
ENTRY(48) , ENTRY(49) , ENTRY(50) , ENTRY(51) ,
ENTRY(52) , ENTRY(53) , ENTRY(54) , ENTRY(55) ,
ENTRY(56) , ENTRY(57) , ENTRY(58) , ENTRY(59) ,
ENTRY(60) , ENTRY(61) , ENTRY(62) , ENTRY(63) ,
ENTRY(64) , ENTRY(65) , ENTRY(66) , ENTRY(67) ,
ENTRY(68) , ENTRY(69) , ENTRY(70) , ENTRY(71) ,
ENTRY(72) , ENTRY(73) , ENTRY(74) , ENTRY(75) ,
ENTRY(76) , ENTRY(77) , ENTRY(78) , ENTRY(79) ,
ENTRY(80) , ENTRY(81) , ENTRY(82) , ENTRY(83) ,
ENTRY(84) , ENTRY(85) , ENTRY(86) , ENTRY(87) ,
ENTRY(88) , ENTRY(89) , ENTRY(90) , ENTRY(91) ,
ENTRY(92) , ENTRY(93) , ENTRY(94) , ENTRY(95) ,
ENTRY(96) , ENTRY(97) , ENTRY(98) , ENTRY(99) ,
ENTRY(100) , ENTRY(101) , ENTRY(102) , ENTRY(103) ,
ENTRY(104) , ENTRY(105) , ENTRY(106) , ENTRY(107) ,
ENTRY(108) , ENTRY(109) , ENTRY(110) , ENTRY(111) ,
ENTRY(112) , ENTRY(113) , ENTRY(114) , ENTRY(115) ,
ENTRY(116) , ENTRY(117) , ENTRY(118) , ENTRY(119) ,
ENTRY(120) , ENTRY(121) , ENTRY(122) , ENTRY(123) ,
ENTRY(124) , ENTRY(125) , ENTRY(126) , ENTRY(127) ,
ENTRY(128) , ENTRY(129) , ENTRY(130) , ENTRY(131) ,
ENTRY(132) , ENTRY(133) , ENTRY(134) , ENTRY(135) ,
ENTRY(136) , ENTRY(137) , ENTRY(138) , ENTRY(139) ,
ENTRY(140) , ENTRY(141) , ENTRY(142) , ENTRY(143) ,
ENTRY(144) , ENTRY(145) , ENTRY(146) , ENTRY(147) ,
ENTRY(148) , ENTRY(149) , ENTRY(150) , ENTRY(151) ,
ENTRY(152) , ENTRY(153) , ENTRY(154) , ENTRY(155) ,
ENTRY(156) , ENTRY(157) , ENTRY(158) , ENTRY(159) ,
ENTRY(160) , ENTRY(161) , ENTRY(162) , ENTRY(163) ,
ENTRY(164) , ENTRY(165) , ENTRY(166) , ENTRY(167) ,
ENTRY(168) , ENTRY(169) , ENTRY(170) , ENTRY(171) ,
ENTRY(172) , ENTRY(173) , ENTRY(174) , ENTRY(175) ,
ENTRY(176) , ENTRY(177) , ENTRY(178) , ENTRY(179) ,
ENTRY(180) , ENTRY(181) , ENTRY(182) , ENTRY(183) ,
ENTRY(184) , ENTRY(185) , ENTRY(186) , ENTRY(187) ,
ENTRY(188) , ENTRY(189) , ENTRY(190) , ENTRY(191) ,
ENTRY(192) , ENTRY(193) , ENTRY(194) , ENTRY(195) ,
ENTRY(196) , ENTRY(197) , ENTRY(198) , ENTRY(199) ,
ENTRY(200) , ENTRY(201) , ENTRY(202) , ENTRY(203) ,
ENTRY(204) , ENTRY(205) , ENTRY(206) , ENTRY(207) ,
ENTRY(208) , ENTRY(209) , ENTRY(210) , ENTRY(211) ,
ENTRY(212) , ENTRY(213) , ENTRY(214) , ENTRY(215) ,
ENTRY(216) , ENTRY(217) , ENTRY(218) , ENTRY(219) ,
ENTRY(220) , ENTRY(221) , ENTRY(222) , ENTRY(223) ,
ENTRY(224) , ENTRY(225) , ENTRY(226) , ENTRY(227) ,
ENTRY(228) , ENTRY(229) , ENTRY(230) , ENTRY(231) ,
ENTRY(232) , ENTRY(233) , ENTRY(234) , ENTRY(235) ,
ENTRY(236) , ENTRY(237) , ENTRY(238) , ENTRY(239) ,
ENTRY(240) , ENTRY(241) , ENTRY(242) , ENTRY(243) ,
ENTRY(244) , ENTRY(245) , ENTRY(246) , ENTRY(247) ,
ENTRY(248) , ENTRY(249) , ENTRY(250) , ENTRY(251) ,
ENTRY(252) , ENTRY(253) , ENTRY(254) , ENTRY(255) ,
#undef ENTRY
#define HUFFDEC_EXTRA_LENGTH_BITS_MASK 0xFF
#define HUFFDEC_LENGTH_BASE_SHIFT 8
#define HUFFDEC_END_OF_BLOCK_LENGTH 0
#define ENTRY(length_base, num_extra_bits) HUFFDEC_RESULT_ENTRY( \
((u32)(length_base) << HUFFDEC_LENGTH_BASE_SHIFT) | (num_extra_bits))
/* End of block */
ENTRY(HUFFDEC_END_OF_BLOCK_LENGTH, 0),
/* Lengths */
ENTRY(3 , 0) , ENTRY(4 , 0) , ENTRY(5 , 0) , ENTRY(6 , 0),
ENTRY(7 , 0) , ENTRY(8 , 0) , ENTRY(9 , 0) , ENTRY(10 , 0),
ENTRY(11 , 1) , ENTRY(13 , 1) , ENTRY(15 , 1) , ENTRY(17 , 1),
ENTRY(19 , 2) , ENTRY(23 , 2) , ENTRY(27 , 2) , ENTRY(31 , 2),
ENTRY(35 , 3) , ENTRY(43 , 3) , ENTRY(51 , 3) , ENTRY(59 , 3),
ENTRY(67 , 4) , ENTRY(83 , 4) , ENTRY(99 , 4) , ENTRY(115, 4),
ENTRY(131, 5) , ENTRY(163, 5) , ENTRY(195, 5) , ENTRY(227, 5),
ENTRY(258, 0) , ENTRY(258, 0) , ENTRY(258, 0) ,
#undef ENTRY
};
/* The decode result for each offset symbol. This is the offset base and the
* number of extra offset bits. */
static const u32 offset_decode_results[DEFLATE_NUM_OFFSET_SYMS] = {
#define HUFFDEC_EXTRA_OFFSET_BITS_SHIFT 16
#define HUFFDEC_OFFSET_BASE_MASK (((u32)1 << HUFFDEC_EXTRA_OFFSET_BITS_SHIFT) - 1)
#define ENTRY(offset_base, num_extra_bits) HUFFDEC_RESULT_ENTRY( \
((u32)(num_extra_bits) << HUFFDEC_EXTRA_OFFSET_BITS_SHIFT) | \
(offset_base))
ENTRY(1 , 0) , ENTRY(2 , 0) , ENTRY(3 , 0) , ENTRY(4 , 0) ,
ENTRY(5 , 1) , ENTRY(7 , 1) , ENTRY(9 , 2) , ENTRY(13 , 2) ,
ENTRY(17 , 3) , ENTRY(25 , 3) , ENTRY(33 , 4) , ENTRY(49 , 4) ,
ENTRY(65 , 5) , ENTRY(97 , 5) , ENTRY(129 , 6) , ENTRY(193 , 6) ,
ENTRY(257 , 7) , ENTRY(385 , 7) , ENTRY(513 , 8) , ENTRY(769 , 8) ,
ENTRY(1025 , 9) , ENTRY(1537 , 9) , ENTRY(2049 , 10) , ENTRY(3073 , 10) ,
ENTRY(4097 , 11) , ENTRY(6145 , 11) , ENTRY(8193 , 12) , ENTRY(12289 , 12) ,
ENTRY(16385 , 13) , ENTRY(24577 , 13) , ENTRY(32769 , 14) , ENTRY(49153 , 14) ,
#undef ENTRY
};
/*
* Build a table for fast decoding of symbols from a Huffman code. As input,
* this function takes the codeword length of each symbol which may be used in
* the code. As output, it produces a decode table for the canonical Huffman
* code described by the codeword lengths. The decode table is built with the
* assumption that it will be indexed with "bit-reversed" codewords, where the
* low-order bit is the first bit of the codeword. This format is used for all
* Huffman codes in DEFLATE.
*
* @decode_table
* The array in which the decode table will be generated. This array must
* have sufficient length; see the definition of the ENOUGH numbers.
* @lens
* An array which provides, for each symbol, the length of the
* corresponding codeword in bits, or 0 if the symbol is unused. This may
* alias @decode_table, since nothing is written to @decode_table until all
* @lens have been consumed. All codeword lengths are assumed to be <=
* @max_codeword_len but are otherwise considered untrusted. If they do
* not form a valid Huffman code, then the decode table is not built and
* %false is returned.
* @num_syms
* The number of symbols in the code, including all unused symbols.
* @decode_results
* An array which provides, for each symbol, the actual value to store into
* the decode table. This value will be directly produced as the result of
* decoding that symbol, thereby moving the indirection out of the decode
* loop and into the table initialization.
* @table_bits
* The log base-2 of the number of main table entries to use.
* @max_codeword_len
* The maximum allowed codeword length for this Huffman code.
* Must be <= DEFLATE_MAX_CODEWORD_LEN.
* @sorted_syms
* A temporary array of length @num_syms.
*
* Returns %true if successful; %false if the codeword lengths do not form a
* valid Huffman code.
*/
static bool
build_decode_table(u32 decode_table[],
const len_t lens[],
const unsigned num_syms,
const u32 decode_results[],
const unsigned table_bits,
const unsigned max_codeword_len,
u16 *sorted_syms)
{
unsigned len_counts[DEFLATE_MAX_CODEWORD_LEN + 1];
unsigned offsets[DEFLATE_MAX_CODEWORD_LEN + 1];
unsigned sym; /* current symbol */
unsigned codeword; /* current codeword, bit-reversed */
unsigned len; /* current codeword length in bits */
unsigned count; /* num codewords remaining with this length */
u32 codespace_used; /* codespace used out of '2^max_codeword_len' */
unsigned cur_table_end; /* end index of current table */
unsigned subtable_prefix; /* codeword prefix of current subtable */
unsigned subtable_start; /* start index of current subtable */
unsigned subtable_bits; /* log2 of current subtable length */
/* Count how many codewords have each length, including 0. */
for (len = 0; len <= max_codeword_len; len++)
len_counts[len] = 0;
for (sym = 0; sym < num_syms; sym++)
len_counts[lens[sym]]++;
/*
* Sort the symbols primarily by increasing codeword length and
* secondarily by increasing symbol value; or equivalently by their
* codewords in lexicographic order, since a canonical code is assumed.
*
* For efficiency, also compute 'codespace_used' in the same pass over
* 'len_counts[]' used to build 'offsets[]' for sorting.
*/
/* Ensure that 'codespace_used' cannot overflow. */
STATIC_ASSERT(sizeof(codespace_used) == 4);
STATIC_ASSERT(UINT32_MAX / (1U << (DEFLATE_MAX_CODEWORD_LEN - 1)) >=
DEFLATE_MAX_NUM_SYMS);
offsets[0] = 0;
offsets[1] = len_counts[0];
codespace_used = 0;
for (len = 1; len < max_codeword_len; len++) {
offsets[len + 1] = offsets[len] + len_counts[len];
codespace_used = (codespace_used << 1) + len_counts[len];
}
codespace_used = (codespace_used << 1) + len_counts[len];
for (sym = 0; sym < num_syms; sym++)
sorted_syms[offsets[lens[sym]]++] = sym;
sorted_syms += offsets[0]; /* Skip unused symbols */
/* lens[] is done being used, so we can write to decode_table[] now. */
/*
* Check whether the lengths form a complete code (exactly fills the
* codespace), an incomplete code (doesn't fill the codespace), or an
* overfull code (overflows the codespace). A codeword of length 'n'
* uses proportion '1/(2^n)' of the codespace. An overfull code is
* nonsensical, so is considered invalid. An incomplete code is
* considered valid only in two specific cases; see below.
*/
/* overfull code? */
if (unlikely(codespace_used > (1U << max_codeword_len)))
return false;
/* incomplete code? */
if (unlikely(codespace_used < (1U << max_codeword_len))) {
u32 entry;
unsigned i;
if (codespace_used == 0) {
/*
* An empty code is allowed. This can happen for the
* offset code in DEFLATE, since a dynamic Huffman block
* need not contain any matches.
*/
/* sym=0, len=1 (arbitrary) */
entry = decode_results[0] | 1;
} else {
/*
* Allow codes with a single used symbol, with codeword
* length 1. The DEFLATE RFC is unclear regarding this
* case. What zlib's decompressor does is permit this
* for the litlen and offset codes and assume the
* codeword is '0' rather than '1'. We do the same
* except we allow this for precodes too, since there's
* no convincing reason to treat the codes differently.
* We also assign both codewords '0' and '1' to the
* symbol to avoid having to handle '1' specially.
*/
if (codespace_used != (1U << (max_codeword_len - 1)) ||
len_counts[1] != 1)
return false;
entry = decode_results[*sorted_syms] | 1;
}
/*
* Note: the decode table still must be fully initialized, in
* case the stream is malformed and contains bits from the part
* of the codespace the incomplete code doesn't use.
*/
for (i = 0; i < (1U << table_bits); i++)
decode_table[i] = entry;
return true;
}
/*
* The lengths form a complete code. Now, enumerate the codewords in
* lexicographic order and fill the decode table entries for each one.
*
* First, process all codewords with len <= table_bits. Each one gets
* '2^(table_bits-len)' direct entries in the table.
*
* Since DEFLATE uses bit-reversed codewords, these entries aren't
* consecutive but rather are spaced '2^len' entries apart. This makes
* filling them naively somewhat awkward and inefficient, since strided
* stores are less cache-friendly and preclude the use of word or
* vector-at-a-time stores to fill multiple entries per instruction.
*
* To optimize this, we incrementally double the table size. When
* processing codewords with length 'len', the table is treated as
* having only '2^len' entries, so each codeword uses just one entry.
* Then, each time 'len' is incremented, the table size is doubled and
* the first half is copied to the second half. This significantly
* improves performance over naively doing strided stores.
*
* Note that some entries copied for each table doubling may not have
* been initialized yet, but it doesn't matter since they're guaranteed
* to be initialized later (because the Huffman code is complete).
*/
codeword = 0;
len = 1;
while ((count = len_counts[len]) == 0)
len++;
cur_table_end = 1U << len;
while (len <= table_bits) {
/* Process all 'count' codewords with length 'len' bits. */
do {
unsigned bit;
/* Fill the first entry for the current codeword. */
decode_table[codeword] =
decode_results[*sorted_syms++] | len;
if (codeword == cur_table_end - 1) {
/* Last codeword (all 1's) */
for (; len < table_bits; len++) {
memcpy(&decode_table[cur_table_end],
decode_table,
cur_table_end *
sizeof(decode_table[0]));
cur_table_end <<= 1;
}
return true;
}
/*
* To advance to the lexicographically next codeword in
* the canonical code, the codeword must be incremented,
* then 0's must be appended to the codeword as needed
* to match the next codeword's length.
*
* Since the codeword is bit-reversed, appending 0's is
* a no-op. However, incrementing it is nontrivial. To
* do so efficiently, use the 'bsr' instruction to find
* the last (highest order) 0 bit in the codeword, set
* it, and clear any later (higher order) 1 bits. But
* 'bsr' actually finds the highest order 1 bit, so to
* use it first flip all bits in the codeword by XOR'ing
* it with (1U << len) - 1 == cur_table_end - 1.
*/
bit = 1U << bsr32(codeword ^ (cur_table_end - 1));
codeword &= bit - 1;
codeword |= bit;
} while (--count);
/* Advance to the next codeword length. */
do {
if (++len <= table_bits) {
memcpy(&decode_table[cur_table_end],
decode_table,
cur_table_end * sizeof(decode_table[0]));
cur_table_end <<= 1;
}
} while ((count = len_counts[len]) == 0);
}
/* Process codewords with len > table_bits. These require subtables. */
cur_table_end = 1U << table_bits;
subtable_prefix = -1;
subtable_start = 0;
for (;;) {
u32 entry;
unsigned i;
unsigned stride;
unsigned bit;
/*
* Start a new subtable if the first 'table_bits' bits of the
* codeword don't match the prefix of the current subtable.
*/
if ((codeword & ((1U << table_bits) - 1)) != subtable_prefix) {
subtable_prefix = (codeword & ((1U << table_bits) - 1));
subtable_start = cur_table_end;
/*
* Calculate the subtable length. If the codeword has
* length 'table_bits + n', then the subtable needs
* '2^n' entries. But it may need more; if fewer than
* '2^n' codewords of length 'table_bits + n' remain,
* then the length will need to be incremented to bring
* in longer codewords until the subtable can be
* completely filled. Note that because the Huffman
* code is complete, it will always be possible to fill
* the subtable eventually.
*/
subtable_bits = len - table_bits;
codespace_used = count;
while (codespace_used < (1U << subtable_bits)) {
subtable_bits++;
codespace_used = (codespace_used << 1) +
len_counts[table_bits + subtable_bits];
}
cur_table_end = subtable_start + (1U << subtable_bits);
/*
* Create the entry that points from the main table to
* the subtable. This entry contains the index of the
* start of the subtable and the number of bits with
* which the subtable is indexed (the log base 2 of the
* number of entries it contains).
*/
decode_table[subtable_prefix] =
HUFFDEC_SUBTABLE_POINTER |
HUFFDEC_RESULT_ENTRY(subtable_start) |
subtable_bits;
}
/* Fill the subtable entries for the current codeword. */
entry = decode_results[*sorted_syms++] | (len - table_bits);
i = subtable_start + (codeword >> table_bits);
stride = 1U << (len - table_bits);
do {
decode_table[i] = entry;
i += stride;
} while (i < cur_table_end);
/* Advance to the next codeword. */
if (codeword == (1U << len) - 1) /* last codeword (all 1's)? */
return true;
bit = 1U << bsr32(codeword ^ ((1U << len) - 1));
codeword &= bit - 1;
codeword |= bit;
count--;
while (count == 0)
count = len_counts[++len];
}
}
/* Build the decode table for the precode. */
static bool
build_precode_decode_table(struct libdeflate_decompressor *d)
{
/* When you change TABLEBITS, you must change ENOUGH, and vice versa! */
STATIC_ASSERT(PRECODE_TABLEBITS == 7 && PRECODE_ENOUGH == 128);
return build_decode_table(d->u.l.precode_decode_table,
d->u.precode_lens,
DEFLATE_NUM_PRECODE_SYMS,
precode_decode_results,
PRECODE_TABLEBITS,
DEFLATE_MAX_PRE_CODEWORD_LEN,
d->sorted_syms);
}
/* Build the decode table for the literal/length code. */
static bool
build_litlen_decode_table(struct libdeflate_decompressor *d,
unsigned num_litlen_syms, unsigned num_offset_syms)
{
/* When you change TABLEBITS, you must change ENOUGH, and vice versa! */
STATIC_ASSERT(LITLEN_TABLEBITS == 10 && LITLEN_ENOUGH == 1334);
return build_decode_table(d->u.litlen_decode_table,
d->u.l.lens,
num_litlen_syms,
litlen_decode_results,
LITLEN_TABLEBITS,
DEFLATE_MAX_LITLEN_CODEWORD_LEN,
d->sorted_syms);
}
/* Build the decode table for the offset code. */
static bool
build_offset_decode_table(struct libdeflate_decompressor *d,
unsigned num_litlen_syms, unsigned num_offset_syms)
{
/* When you change TABLEBITS, you must change ENOUGH, and vice versa! */
STATIC_ASSERT(OFFSET_TABLEBITS == 8 && OFFSET_ENOUGH == 402);
return build_decode_table(d->offset_decode_table,
d->u.l.lens + num_litlen_syms,
num_offset_syms,
offset_decode_results,
OFFSET_TABLEBITS,
DEFLATE_MAX_OFFSET_CODEWORD_LEN,
d->sorted_syms);
}
static forceinline machine_word_t
repeat_byte(u8 b)
{
machine_word_t v;
STATIC_ASSERT(WORDBITS == 32 || WORDBITS == 64);
v = b;
v |= v << 8;
v |= v << 16;
v |= v << ((WORDBITS == 64) ? 32 : 0);
return v;
}
static forceinline void
copy_word_unaligned(const void *src, void *dst)
{
store_word_unaligned(load_word_unaligned(src), dst);
}
/*****************************************************************************
* Main decompression routine
*****************************************************************************/
typedef enum libdeflate_result (*decompress_func_t)
(struct libdeflate_decompressor * restrict d,
const void * restrict in, size_t in_nbytes,
void * restrict out, size_t out_nbytes_avail,
size_t *actual_in_nbytes_ret, size_t *actual_out_nbytes_ret);
#undef DEFAULT_IMPL
#undef DISPATCH
#if defined(__i386__) || defined(__x86_64__)
# include "x86/decompress_impl.h"
#endif
#ifndef DEFAULT_IMPL
# define FUNCNAME deflate_decompress_default
# define ATTRIBUTES
# include "decompress_template.h"
# define DEFAULT_IMPL deflate_decompress_default
#endif
#ifdef DISPATCH
static enum libdeflate_result
dispatch(struct libdeflate_decompressor * restrict d,
const void * restrict in, size_t in_nbytes,
void * restrict out, size_t out_nbytes_avail,
size_t *actual_in_nbytes_ret, size_t *actual_out_nbytes_ret);
static volatile decompress_func_t decompress_impl = dispatch;
/* Choose the fastest implementation at runtime */
static enum libdeflate_result
dispatch(struct libdeflate_decompressor * restrict d,
const void * restrict in, size_t in_nbytes,
void * restrict out, size_t out_nbytes_avail,
size_t *actual_in_nbytes_ret, size_t *actual_out_nbytes_ret)
{
decompress_func_t f = arch_select_decompress_func();
if (f == NULL)
f = DEFAULT_IMPL;
decompress_impl = f;
return (*f)(d, in, in_nbytes, out, out_nbytes_avail,
actual_in_nbytes_ret, actual_out_nbytes_ret);
}
#else
# define decompress_impl DEFAULT_IMPL /* only one implementation, use it */
#endif
/*
* This is the main DEFLATE decompression routine. See libdeflate.h for the
* documentation.
*
* Note that the real code is in decompress_template.h. The part here just
* handles calling the appropriate implementation depending on the CPU features
* at runtime.
*/
LIBDEFLATEAPI enum libdeflate_result
libdeflate_deflate_decompress_ex(struct libdeflate_decompressor * restrict d,
const void * restrict in, size_t in_nbytes,
void * restrict out, size_t out_nbytes_avail,
size_t *actual_in_nbytes_ret,
size_t *actual_out_nbytes_ret)
{
return decompress_impl(d, in, in_nbytes, out, out_nbytes_avail,
actual_in_nbytes_ret, actual_out_nbytes_ret);
}
LIBDEFLATEAPI enum libdeflate_result
libdeflate_deflate_decompress(struct libdeflate_decompressor * restrict d,
const void * restrict in, size_t in_nbytes,
void * restrict out, size_t out_nbytes_avail,
size_t *actual_out_nbytes_ret)
{
return libdeflate_deflate_decompress_ex(d, in, in_nbytes,
out, out_nbytes_avail,
NULL, actual_out_nbytes_ret);
}
LIBDEFLATEAPI struct libdeflate_decompressor *
libdeflate_alloc_decompressor(void)
{
/*
* Note that only certain parts of the decompressor actually must be
* initialized here:
*
* - 'static_codes_loaded' must be initialized to false.
*
* - The first half of the main portion of each decode table must be
* initialized to any value, to avoid reading from uninitialized
* memory during table expansion in build_decode_table(). (Although,
* this is really just to avoid warnings with dynamic tools like
* valgrind, since build_decode_table() is guaranteed to initialize
* all entries eventually anyway.)
*
* But for simplicity, we currently just zero the whole decompressor.
*/
return calloc(1, sizeof(struct libdeflate_decompressor));
}
LIBDEFLATEAPI void
libdeflate_free_decompressor(struct libdeflate_decompressor *d)
{
free(d);
}
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