lib: crc32_sw: 4 bit at a time implementation (4e7b5769) · Commits · Wenxi XU / zephyr

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>

lib/os/crc32_sw.c

+12 −4

Original line number	Diff line number	Diff line
		@@ -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 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,
		};

		crc = ~crc;

		for (size_t i = 0; i < len; i++) {
		crc = crc ^ data[i];
		uint8_t byte = data[i];

		for (uint8_t j = 0; j < 8; j++) {
		crc = (crc >> 1) ^ (0xEDB88320 & -(crc & 1));
		}
		crc = (crc >> 4) ^ table[(crc ^ byte) & 0x0f];
		crc = (crc >> 4) ^ table[(crc ^ (byte >> 4)) & 0x0f];
		}

		return (~crc);

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