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split fill table endians, mark consts

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This commit is contained in:
Connor Olding 2015-04-11 11:04:03 -07:00
parent 4524ecba1a
commit 2ce38461bb
2 changed files with 35 additions and 12 deletions
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42
crc32.c
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@ -13,35 +13,55 @@ crc_reflect(uint32_t input)
} }
static inline void static inline void
crc_fill_table(uint32_t *table, int big, uint32_t polynomial) crc_be_fill_table(uint32_t *table, uint32_t polynomial)
{ {
uint32_t lsb = (big) ? 1 << 31 : 1; /* least significant bit */ const uint32_t lsb = 1 << 31;
uint32_t poly = (big) ? polynomial : crc_reflect(polynomial); uint32_t poly = polynomial;
for (int c = 0; c < CRC_TABLE_SIZE; c++, table++) { for (int c = 0; c < CRC_TABLE_SIZE; c++, table++) {
*table = (big) ? c << 24 : c; uint32_t v = c << 24;
for (int i = 0; i < 8; i++) { for (int i = 0; i < 8; i++) {
if (*table & lsb) { if (v & lsb) {
*table = (big) ? *table << 1 : *table >> 1; v <<= 1;
*table ^= poly; v ^= poly;
} else { } else {
*table = (big) ? *table << 1 : *table >> 1; v <<= 1;
} }
*table &= 0xFFFFFFFF;
} }
*table = v;
}
}
static inline void
crc_le_fill_table(uint32_t *table, uint32_t polynomial)
{
const uint32_t lsb = 1;
uint32_t poly = crc_reflect(polynomial);
for (int c = 0; c < CRC_TABLE_SIZE; c++, table++) {
uint32_t v = c;
for (int i = 0; i < 8; i++) {
if (v & lsb) {
v >>= 1;
v ^= poly;
} else {
v >>= 1;
}
}
*table = v;
} }
} }
static inline void static inline void
crc_be_cycle(uint32_t *table, uint32_t *remainder, char c) crc_be_cycle(uint32_t *table, uint32_t *remainder, char c)
{ {
uint32_t byte = table[(((*remainder) >> 24) ^ c) & 0xff]; const uint32_t byte = table[(((*remainder) >> 24) ^ c) & 0xFF];
*remainder = (((*remainder) << 8) ^ byte) & 0xFFFFFFFF; *remainder = (((*remainder) << 8) ^ byte) & 0xFFFFFFFF;
} }
static inline void static inline void
crc_le_cycle(uint32_t *table, uint32_t *remainder, char c) crc_le_cycle(uint32_t *table, uint32_t *remainder, char c)
{ {
uint32_t byte = table[((*remainder) ^ c) & 0xFF]; const uint32_t byte = table[((*remainder) ^ c) & 0xFF];
*remainder = ((*remainder) >> 8) ^ byte; *remainder = ((*remainder) >> 8) ^ byte;
} }

5
main.c
View file

@ -127,7 +127,10 @@ cycle_file(FILE *stream)
(big_endian) ? crc_be_cycle : crc_le_cycle; (big_endian) ? crc_be_cycle : crc_le_cycle;
uint32_t table[CRC_TABLE_SIZE]; uint32_t table[CRC_TABLE_SIZE];
crc_fill_table(table, big_endian, polynomial); if (big_endian)
crc_be_fill_table(table, polynomial);
else
crc_le_fill_table(table, polynomial);
do { do {
int len = fread(buff, 1, BUFFER_SIZE, stream); int len = fread(buff, 1, BUFFER_SIZE, stream);
if (ferror(stream)) { if (ferror(stream)) {