bsnes/nall/hash/crc16.hpp

56 lines
1.0 KiB
C++
Executable File

#pragma once
#include <nall/hash/hash.hpp>
namespace nall::Hash {
struct CRC16 : Hash {
using Hash::input;
CRC16(array_view<uint8_t> buffer = {}) {
reset();
input(buffer);
}
auto reset() -> void override {
checksum = ~0;
}
auto input(uint8_t value) -> void override {
checksum = (checksum >> 8) ^ table(checksum ^ value);
}
auto output() const -> vector<uint8_t> override {
vector<uint8_t> result;
for(auto n : reverse(range(2))) result.append(~checksum >> n * 8);
return result;
}
auto value() const -> uint16_t {
return ~checksum;
}
private:
static auto table(uint8_t index) -> uint16_t {
static uint16_t table[256] = {0};
static bool initialized = false;
if(!initialized) {
initialized = true;
for(auto index : range(256)) {
uint16_t crc = index;
for(auto bit : range(8)) {
crc = (crc >> 1) ^ (crc & 1 ? 0x8408 : 0);
}
table[index] = crc;
}
}
return table[index];
}
uint16_t checksum = 0;
};
}