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lib: crc32_sw: 4 bit at a time implementation

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Calculate crc32 4 bits at a time. The return value of the calculation is
identical to the previous 1 bit at a time implementation.

Results in a speed up of a factor 3 at the cost of using 64 bytes of
flash for a crc table.

Calculating crc32 of 128kB of flash on a 120MHz Kinetis MKE16F512
Cortex-M4 takes 99ms using the 1 bit at a time implementation, and 30ms
using the 4 bits at a time implementation.

The crc32 routine is used by subsys/canbus/canopen/canopen_program.c to
calculate crc of flash images.

Signed-off-by: Klaus H. Sorensen <khso@vestas.com>
This commit is contained in:
Klaus H. Sorensen 2021-01-15 16:24:21 +01:00 • committed by Anas Nashif
commit 4e7b5769bd
1 changed files with 14 additions and 6 deletions
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20
lib/os/crc32_sw.c
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@ -13,13 +13,21 @@ uint32_t crc32_ieee(const uint8_t *data, size_t len)
uint32_t crc32_ieee_update(uint32_t crc, const uint8_t *data, size_t len)
{
crc = ~crc;
for (size_t i = 0; i < len; i++) {
crc = crc ^ data[i];
/* crc table generated from polynomial 0xedb88320 */
static const uint32_t table[16] = {
0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac,
0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c,
0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c,
};
for (uint8_t j = 0; j < 8; j++) {
crc = (crc >> 1) ^ (0xEDB88320 & -(crc & 1));
}
crc = ~crc;
for (size_t i = 0; i < len; i++) {
uint8_t byte = data[i];
crc = (crc >> 4) ^ table[(crc ^ byte) & 0x0f];
crc = (crc >> 4) ^ table[(crc ^ (byte >> 4)) & 0x0f];
}
return (~crc);