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nxdumptool/source/crc32_fast.c
2020-04-15 20:06:41 -04:00

51 lines
1.7 KiB
C

/* Standard CRC32 checksum: fast public domain implementation for
* little-endian architectures. Written for compilation with an
* optimizer set to perform loop unwinding. Outputs the checksum for
* each file given as a command line argument. Invalid file names and
* files that cause errors are silently skipped. The program reads
* from stdin if it is called with no arguments. */
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <switch/types.h>
u32 crc32_for_byte(u32 r)
{
for(int j = 0; j < 8; ++j) r = (r & 1 ? 0 : (u32)0xEDB88320L) ^ r >> 1;
return r ^ (u32)0xFF000000L;
}
/* Any unsigned integer type with at least 32 bits may be used as
* accumulator type for fast crc32-calulation, but unsigned long is
* probably the optimal choice for most systems. */
typedef unsigned long accum_t;
void init_tables(u32 *table, u32 *wtable)
{
for(u64 i = 0; i < 0x100; ++i) table[i] = crc32_for_byte(i);
for(u64 k = 0; k < sizeof(accum_t); ++k)
{
for(u64 w, i = 0; i < 0x100; ++i)
{
for(u64 j = w = 0; j < sizeof(accum_t); ++j) w = table[(u8)(j == k ? w ^ i : w)] ^ w >> 8;
wtable[(k << 8) + i] = w ^ (k ? wtable[0] : 0);
}
}
}
void crc32(const void *data, u64 n_bytes, u32 *crc)
{
static u32 table[0x100], wtable[0x100 * sizeof(accum_t)];
u64 n_accum = n_bytes / sizeof(accum_t);
if (!*table) init_tables(table, wtable);
for(u64 i = 0; i < n_accum; ++i)
{
accum_t a = *crc ^ ((accum_t*)data)[i];
for(u64 j = *crc = 0; j < sizeof(accum_t); ++j) *crc ^= wtable[(j << 8) + (u8)(a >> 8 * j)];
}
for(u64 i = n_accum * sizeof(accum_t); i < n_bytes; ++i) *crc = table[(u8)*crc ^ ((u8*)data)[i]] ^ *crc >> 8;
}