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/*
* Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
namespace Compress {
// RFC 1951 - 3.2.5
static constexpr struct {
u16 symbol;
u16 base_length;
u16 extra_bits;
} packed_length_symbols[29] = {
{ 257, 3, 0 },
{ 258, 4, 0 },
{ 259, 5, 0 },
{ 260, 6, 0 },
{ 261, 7, 0 },
{ 262, 8, 0 },
{ 263, 9, 0 },
{ 264, 10, 0 },
{ 265, 11, 1 },
{ 266, 13, 1 },
{ 267, 15, 1 },
{ 268, 17, 1 },
{ 269, 19, 2 },
{ 270, 23, 2 },
{ 271, 27, 2 },
{ 272, 31, 2 },
{ 273, 35, 3 },
{ 274, 43, 3 },
{ 275, 51, 3 },
{ 276, 59, 3 },
{ 277, 67, 4 },
{ 278, 83, 4 },
{ 279, 99, 4 },
{ 280, 115, 4 },
{ 281, 131, 5 },
{ 282, 163, 5 },
{ 283, 195, 5 },
{ 284, 227, 5 },
{ 285, 258, 0 }
};
// RFC 1951 - 3.2.5
static constexpr struct {
u16 symbol;
u16 base_distance;
u16 extra_bits;
} packed_distances[31] = {
{ 0, 1, 0 },
{ 1, 2, 0 },
{ 2, 3, 0 },
{ 3, 4, 0 },
{ 4, 5, 1 },
{ 5, 7, 1 },
{ 6, 9, 2 },
{ 7, 13, 2 },
{ 8, 17, 3 },
{ 9, 25, 3 },
{ 10, 33, 4 },
{ 11, 49, 4 },
{ 12, 65, 5 },
{ 13, 97, 5 },
{ 14, 129, 6 },
{ 15, 193, 6 },
{ 16, 257, 7 },
{ 17, 385, 7 },
{ 18, 513, 8 },
{ 19, 769, 8 },
{ 20, 1025, 9 },
{ 21, 1537, 9 },
{ 22, 2049, 10 },
{ 23, 3073, 10 },
{ 24, 4097, 11 },
{ 25, 6145, 11 },
{ 26, 8193, 12 },
{ 27, 12289, 12 },
{ 28, 16385, 13 },
{ 29, 24577, 13 },
{ 30, 32 * KiB + 1, 0 }, // signifies end
};
// RFC 1951 - 3.2.6
static constexpr struct {
u16 base_value;
u16 bits;
} fixed_literal_bits[5] = {
{ 0, 8 },
{ 144, 9 },
{ 256, 7 },
{ 280, 8 },
{ 288, 0 } // signifies end
};
// RFC 1951 - 3.2.7
static constexpr size_t code_lengths_code_lengths_order[] { 16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15 };
static consteval Array<u16, 259> generate_length_to_symbol()
{
Array<u16, 259> array = { UINT16_MAX, UINT16_MAX, UINT16_MAX }; // there are 256 valid lengths (3-258) + 3 invalid lengths (0-2)
size_t base_length = 0;
for (size_t len = 3; len < 259; len++) {
if (len == packed_length_symbols[base_length + 1].base_length)
base_length++;
array[len] = packed_length_symbols[base_length].symbol;
}
return array;
};
static constexpr auto length_to_symbol = generate_length_to_symbol();
static consteval Array<u16, 256> generate_distance_to_base_lo()
{
Array<u16, 256> array;
size_t base_distance = 0;
for (size_t dist = 1; dist <= 256; dist++) {
if (dist == packed_distances[base_distance + 1].base_distance)
base_distance++;
array[dist - 1] = packed_distances[base_distance].symbol;
}
return array;
};
static constexpr auto distance_to_base_lo = generate_distance_to_base_lo();
static consteval Array<u16, 256> generate_distance_to_base_hi()
{
Array<u16, 256> array = { UINT16_MAX, UINT16_MAX };
size_t base_distance = 16;
for (size_t dist = 257; dist <= 32 * KiB; dist++) {
if (dist == packed_distances[base_distance + 1].base_distance)
base_distance++;
array[(dist - 1) >> 7] = packed_distances[base_distance].symbol;
}
return array;
};
static constexpr auto distance_to_base_hi = generate_distance_to_base_hi();
static consteval Array<u8, 288> generate_fixed_literal_bit_lengths()
{
Array<u8, 288> array;
for (size_t i = 0; i < 4; i++) {
array.span().slice(fixed_literal_bits[i].base_value, fixed_literal_bits[i + 1].base_value - fixed_literal_bits[i].base_value).fill(fixed_literal_bits[i].bits);
}
return array;
};
static constexpr auto fixed_literal_bit_lengths = generate_fixed_literal_bit_lengths();
static consteval Array<u8, 32> generate_fixed_distance_bit_lengths()
{
Array<u8, 32> array;
array.fill(5);
return array;
};
static constexpr auto fixed_distance_bit_lengths = generate_fixed_distance_bit_lengths();
static consteval u8 reverse8(u8 value)
{
u8 result = 0;
for (size_t i = 0; i < 8; i++) {
if (value & (1 << i))
result |= 1 << (7 - i);
}
return result;
}
static consteval Array<u8, UINT8_MAX + 1> generate_reverse8_lookup_table()
{
Array<u8, UINT8_MAX + 1> array;
for (size_t i = 0; i <= UINT8_MAX; i++) {
array[i] = reverse8(i);
}
return array;
}
static constexpr auto reverse8_lookup_table = generate_reverse8_lookup_table();
// Lookup-table based bit swap
ALWAYS_INLINE static u16 fast_reverse16(u16 value, size_t bits)
{
VERIFY(bits <= 16);
u16 lo = value & 0xff;
u16 hi = value >> 8;
u16 reversed = (u16)((reverse8_lookup_table[lo] << 8) | reverse8_lookup_table[hi]);
return reversed >> (16 - bits);
}
}
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