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Add support for the reversed CRC algorithm to CRC module

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This commit is contained in:
Mario Hüttel 2023-01-15 21:12:20 +01:00
parent 84c60fc461
commit 6f40e37e81
1 changed files with 65 additions and 9 deletions
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68
src/crc.c
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@ -34,13 +34,26 @@ int crc_len_from_poly(uint64_t polynomial)
return pos; return pos;
} }
static uint32_t reverse_short_poly(uint32_t poly, uint8_t len)
{
uint8_t i;
uint32_t ret = 0ul;
for (i = 0; i < len; i++) {
ret <<= 1;
ret |= (poly & 1u);
poly >>= 1;
}
return ret;
}
static uint64_t shorten_polynomial(uint64_t poly) static uint64_t shorten_polynomial(uint64_t poly)
{ {
int i; int i;
for (i = 32; i >= 0; i--) {
for (i = 31; i <= 0; i--) { if (poly & ((uint64_t)1ull << i)) {
if (poly & (1 << i)) { poly &= ~((uint64_t)1ull<<i);
poly &= ~(1<<i);
break; break;
} }
} }
@ -55,15 +68,22 @@ static void internal_push_byte(struct crc_calc *crc, const uint8_t *data, size_t
crc_val = crc->crc_val; crc_val = crc->crc_val;
if (crc->settings.rev) {
for (i = 0; i < len; i++, data++) {
crc_val = (crc_val >> 8) ^ crc->table[((crc_val & 0xFF) ^ *data)];
}
} else {
/* Non reversed algo */
for (i = 0; i < len; i++, data++) { for (i = 0; i < len; i++, data++) {
crc_val = ((crc_val << 8) & crc->crc_mask) ^ crc_val = ((crc_val << 8) & crc->crc_mask) ^
crc->table[((crc_val >> (crc->crc_length-8u)) & 0xff) ^ *data]; crc->table[((crc_val >> (crc->crc_length-8u)) & 0xff) ^ *data];
} }
}
crc->crc_val = crc_val; crc->crc_val = crc_val;
} }
static void fill_crc_table(struct crc_calc *crc) static void fill_crc_table_non_reversed(struct crc_calc *crc)
{ {
uint32_t input; uint32_t input;
uint32_t crc_reg; uint32_t crc_reg;
@ -87,10 +107,46 @@ static void fill_crc_table(struct crc_calc *crc)
crc_reg <<= 1; crc_reg <<= 1;
} }
} }
crc->table[input] = crc_reg; crc->table[input] = crc_reg & crc->crc_mask;
} }
} }
static void fill_crc_table_reversed(struct crc_calc *crc)
{
uint32_t input;
uint32_t crc_reg;
uint32_t short_poly;
int i;
short_poly = (uint32_t)shorten_polynomial(crc->settings.polynomial);
printf("Short (pre): 0x%x\n", short_poly);
short_poly = reverse_short_poly(short_poly, crc->crc_length);
printf("Short (post): 0x%x\n", short_poly);
for (input = 0; input <= 255u; input++) {
crc_reg = (uint32_t)input;
for (i = 0; i < 8; i++) {
/* Check LSB for reversed CRC shifting */
if (crc_reg & 1u) {
crc_reg >>= 1;
crc_reg ^= short_poly;
} else {
crc_reg >>= 1;
}
}
crc->table[input] = crc_reg & crc->crc_mask;
}
}
static void fill_crc_table(struct crc_calc *crc)
{
if (crc->settings.rev)
fill_crc_table_reversed(crc);
else
fill_crc_table_non_reversed(crc);
}
void crc_init(struct crc_calc *crc, const struct crc_settings *settings) void crc_init(struct crc_calc *crc, const struct crc_settings *settings)
{ {
uint32_t i; uint32_t i;