Created
February 16, 2017 11:39
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simplest crc32 c++ implementation
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#pragma once | |
#include <stdint.h> | |
struct crc32 | |
{ | |
static void generate_table(uint32_t(&table)[256]) | |
{ | |
uint32_t polynomial = 0xEDB88320; | |
for (uint32_t i = 0; i < 256; i++) | |
{ | |
uint32_t c = i; | |
for (size_t j = 0; j < 8; j++) | |
{ | |
if (c & 1) { | |
c = polynomial ^ (c >> 1); | |
} | |
else { | |
c >>= 1; | |
} | |
} | |
table[i] = c; | |
} | |
} | |
static uint32_t update(uint32_t (&table)[256], uint32_t initial, const void* buf, size_t len) | |
{ | |
uint32_t c = initial ^ 0xFFFFFFFF; | |
const uint8_t* u = static_cast<const uint8_t*>(buf); | |
for (size_t i = 0; i < len; ++i) | |
{ | |
c = table[(c ^ u[i]) & 0xFF] ^ (c >> 8); | |
} | |
return c ^ 0xFFFFFFFF; | |
} | |
}; | |
// usage: the following code generates crc for 2 pieces of data | |
// uint32_t table[256]; | |
// crc32::generate_table(table); | |
// uint32_t crc = crc32::update(table, 0, data_piece1, len1); | |
// crc = crc32::update(table, crc, data_piece2, len2); | |
// output(crc); |
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With class: