/* Copyright 2013 Google Inc. All Rights Reserved. Distributed under MIT license. See file LICENSE for detail or copy at https://opensource.org/licenses/MIT */ /* Utilities for building Huffman decoding tables. */ #include "huffman.h" #include <string.h> /* memcpy, memset */ #include "../common/constants.h" #include "../common/platform.h" #include <brotli/types.h> #if defined(__cplusplus) || defined(c_plusplus) extern "C" { #endif #define BROTLI_REVERSE_BITS_MAX 8 #if defined(BROTLI_RBIT) #define BROTLI_REVERSE_BITS_BASE \ ((sizeof(brotli_reg_t) << 3) - BROTLI_REVERSE_BITS_MAX) #else #define BROTLI_REVERSE_BITS_BASE 0 static uint8_t kReverseBits[1 << BROTLI_REVERSE_BITS_MAX] = { 0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0, 0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0, 0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8, 0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8, 0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4, 0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4, 0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC, 0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC, 0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2, 0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2, 0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA, 0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA, 0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6, 0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6, 0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE, 0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE, 0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1, 0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1, 0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9, 0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9, 0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5, 0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5, 0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED, 0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD, 0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3, 0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3, 0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB, 0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB, 0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7, 0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7, 0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF, 0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF }; #endif /* BROTLI_RBIT */ #define BROTLI_REVERSE_BITS_LOWEST \ ((brotli_reg_t)1 << (BROTLI_REVERSE_BITS_MAX - 1 + BROTLI_REVERSE_BITS_BASE)) /* Returns reverse(num >> BROTLI_REVERSE_BITS_BASE, BROTLI_REVERSE_BITS_MAX), where reverse(value, len) is the bit-wise reversal of the len least significant bits of value. */ static BROTLI_INLINE brotli_reg_t BrotliReverseBits(brotli_reg_t num) { #if defined(BROTLI_RBIT) return BROTLI_RBIT(num); #else return kReverseBits[num]; #endif } /* Stores code in table[0], table[step], table[2*step], ..., table[end] */ /* Assumes that end is an integer multiple of step */ static BROTLI_INLINE void ReplicateValue(HuffmanCode* table, int step, int end, HuffmanCode code) { do { end -= step; table[end] = code; } while (end > 0); } /* Returns the table width of the next 2nd level table. |count| is the histogram of bit lengths for the remaining symbols, |len| is the code length of the next processed symbol. */ static BROTLI_INLINE int NextTableBitSize(const uint16_t* const count, int len, int root_bits) { int left = 1 << (len - root_bits); while (len < BROTLI_HUFFMAN_MAX_CODE_LENGTH) { left -= count[len]; if (left <= 0) break; ++len; left <<= 1; } return len - root_bits; } void BrotliBuildCodeLengthsHuffmanTable(HuffmanCode* table, const uint8_t* const code_lengths, uint16_t* count) { HuffmanCode code; /* current table entry */ int symbol; /* symbol index in original or sorted table */ brotli_reg_t key; /* prefix code */ brotli_reg_t key_step; /* prefix code addend */ int step; /* step size to replicate values in current table */ int table_size; /* size of current table */ int sorted[BROTLI_CODE_LENGTH_CODES]; /* symbols sorted by code length */ /* offsets in sorted table for each length */ int offset[BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH + 1]; int bits; int bits_count; BROTLI_DCHECK(BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH <= BROTLI_REVERSE_BITS_MAX); /* Generate offsets into sorted symbol table by code length. */ symbol = -1; bits = 1; BROTLI_REPEAT(BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH, { symbol += count[bits]; offset[bits] = symbol; bits++; }); /* Symbols with code length 0 are placed after all other symbols. */ offset[0] = BROTLI_CODE_LENGTH_CODES - 1; /* Sort symbols by length, by symbol order within each length. */ symbol = BROTLI_CODE_LENGTH_CODES; do { BROTLI_REPEAT(6, { symbol--; sorted[offset[code_lengths[symbol]]--] = symbol; }); } while (symbol != 0); table_size = 1 << BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH; /* Special case: all symbols but one have 0 code length. */ if (offset[0] == 0) { code = ConstructHuffmanCode(0, (uint16_t)sorted[0]); for (key = 0; key < (brotli_reg_t)table_size; ++key) { table[key] = code; } return; } /* Fill in table. */ key = 0; key_step = BROTLI_REVERSE_BITS_LOWEST; symbol = 0; bits = 1; step = 2; do { for (bits_count = count[bits]; bits_count != 0; --bits_count) { code = ConstructHuffmanCode((uint8_t)bits, (uint16_t)sorted[symbol++]); ReplicateValue(&table[BrotliReverseBits(key)], step, table_size, code); key += key_step; } step <<= 1; key_step >>= 1; } while (++bits <= BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH); } uint32_t BrotliBuildHuffmanTable(HuffmanCode* root_table, int root_bits, const uint16_t* const symbol_lists, uint16_t* count) { HuffmanCode code; /* current table entry */ HuffmanCode* table; /* next available space in table */ int len; /* current code length */ int symbol; /* symbol index in original or sorted table */ brotli_reg_t key; /* prefix code */ brotli_reg_t key_step; /* prefix code addend */ brotli_reg_t sub_key; /* 2nd level table prefix code */ brotli_reg_t sub_key_step; /* 2nd level table prefix code addend */ int step; /* step size to replicate values in current table */ int table_bits; /* key length of current table */ int table_size; /* size of current table */ int total_size; /* sum of root table size and 2nd level table sizes */ int max_length = -1; int bits; int bits_count; BROTLI_DCHECK(root_bits <= BROTLI_REVERSE_BITS_MAX); BROTLI_DCHECK(BROTLI_HUFFMAN_MAX_CODE_LENGTH - root_bits <= BROTLI_REVERSE_BITS_MAX); while (symbol_lists[max_length] == 0xFFFF) max_length--; max_length += BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1; table = root_table; table_bits = root_bits; table_size = 1 << table_bits; total_size = table_size; /* Fill in the root table. Reduce the table size to if possible, and create the repetitions by memcpy. */ if (table_bits > max_length) { table_bits = max_length; table_size = 1 << table_bits; } key = 0; key_step = BROTLI_REVERSE_BITS_LOWEST; bits = 1; step = 2; do { symbol = bits - (BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1); for (bits_count = count[bits]; bits_count != 0; --bits_count) { symbol = symbol_lists[symbol]; code = ConstructHuffmanCode((uint8_t)bits, (uint16_t)symbol); ReplicateValue(&table[BrotliReverseBits(key)], step, table_size, code); key += key_step; } step <<= 1; key_step >>= 1; } while (++bits <= table_bits); /* If root_bits != table_bits then replicate to fill the remaining slots. */ while (total_size != table_size) { memcpy(&table[table_size], &table[0], (size_t)table_size * sizeof(table[0])); table_size <<= 1; } /* Fill in 2nd level tables and add pointers to root table. */ key_step = BROTLI_REVERSE_BITS_LOWEST >> (root_bits - 1); sub_key = (BROTLI_REVERSE_BITS_LOWEST << 1); sub_key_step = BROTLI_REVERSE_BITS_LOWEST; for (len = root_bits + 1, step = 2; len <= max_length; ++len) { symbol = len - (BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1); for (; count[len] != 0; --count[len]) { if (sub_key == (BROTLI_REVERSE_BITS_LOWEST << 1U)) { table += table_size; table_bits = NextTableBitSize(count, len, root_bits); table_size = 1 << table_bits; total_size += table_size; sub_key = BrotliReverseBits(key); key += key_step; root_table[sub_key] = ConstructHuffmanCode( (uint8_t)(table_bits + root_bits), (uint16_t)(((size_t)(table - root_table)) - sub_key)); sub_key = 0; } symbol = symbol_lists[symbol]; code = ConstructHuffmanCode((uint8_t)(len - root_bits), (uint16_t)symbol); ReplicateValue( &table[BrotliReverseBits(sub_key)], step, table_size, code); sub_key += sub_key_step; } step <<= 1; sub_key_step >>= 1; } return (uint32_t)total_size; } uint32_t BrotliBuildSimpleHuffmanTable(HuffmanCode* table, int root_bits, uint16_t* val, uint32_t num_symbols) { uint32_t table_size = 1; const uint32_t goal_size = 1U << root_bits; switch (num_symbols) { case 0: table[0] = ConstructHuffmanCode(0, val[0]); break; case 1: if (val[1] > val[0]) { table[0] = ConstructHuffmanCode(1, val[0]); table[1] = ConstructHuffmanCode(1, val[1]); } else { table[0] = ConstructHuffmanCode(1, val[1]); table[1] = ConstructHuffmanCode(1, val[0]); } table_size = 2; break; case 2: table[0] = ConstructHuffmanCode(1, val[0]); table[2] = ConstructHuffmanCode(1, val[0]); if (val[2] > val[1]) { table[1] = ConstructHuffmanCode(2, val[1]); table[3] = ConstructHuffmanCode(2, val[2]); } else { table[1] = ConstructHuffmanCode(2, val[2]); table[3] = ConstructHuffmanCode(2, val[1]); } table_size = 4; break; case 3: { int i, k; for (i = 0; i < 3; ++i) { for (k = i + 1; k < 4; ++k) { if (val[k] < val[i]) { uint16_t t = val[k]; val[k] = val[i]; val[i] = t; } } } table[0] = ConstructHuffmanCode(2, val[0]); table[2] = ConstructHuffmanCode(2, val[1]); table[1] = ConstructHuffmanCode(2, val[2]); table[3] = ConstructHuffmanCode(2, val[3]); table_size = 4; break; } case 4: { if (val[3] < val[2]) { uint16_t t = val[3]; val[3] = val[2]; val[2] = t; } table[0] = ConstructHuffmanCode(1, val[0]); table[1] = ConstructHuffmanCode(2, val[1]); table[2] = ConstructHuffmanCode(1, val[0]); table[3] = ConstructHuffmanCode(3, val[2]); table[4] = ConstructHuffmanCode(1, val[0]); table[5] = ConstructHuffmanCode(2, val[1]); table[6] = ConstructHuffmanCode(1, val[0]); table[7] = ConstructHuffmanCode(3, val[3]); table_size = 8; break; } } while (table_size != goal_size) { memcpy(&table[table_size], &table[0], (size_t)table_size * sizeof(table[0])); table_size <<= 1; } return goal_size; } #if defined(__cplusplus) || defined(c_plusplus) } /* extern "C" */ #endif