openmv/ports/alif/omv_crc.c
iabdalkader 75a2a7a2d5 ports/alif: Use direct CRC calculation for unaligned bytes
Replace lookup table with bit-by-bit polynomial calculation for
the remaining 1-3 bytes. Direct calculation is faster than table
lookup for such small amounts due to avoiding cache misses and
memory indirection overhead that dominates when processing only
1-3 bytes.

Signed-off-by: iabdalkader <i.abdalkader@gmail.com>
2025-09-26 19:46:48 +02:00

108 lines
3.4 KiB
C

/*
* SPDX-License-Identifier: MIT
*
* Copyright (C) 2023-2024 OpenMV, LLC.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "crc.h"
#include "global_map.h"
#include "omv_crc.h"
#define CRC0 ((CRC_Type *) CRC0_BASE)
static bool crc32_initialized = false;
static void crc_calculate(CRC_Type *crc, const void *buf, uint32_t len, uint32_t *value);
static void omv_crc32_init(void) {
CRC0->CRC_CONTROL = CRC_32C |
CRC_BYTE_SWAP |
CRC_CUSTOM_POLY |
CRC_ALGO_32_BIT_SIZE;
CRC0->CRC_SEED = OMV_CRC32_INIT;
CRC0->CRC_POLY_CUSTOM = OMV_CRC32_POLY;
crc32_initialized = true;
}
uint32_t omv_crc32_start(const void *buf, size_t len) {
uint32_t result = OMV_CRC32_INIT;
if (!crc32_initialized) {
omv_crc32_init();
}
if (len == 0) {
return OMV_CRC32_INIT;
}
crc_calculate(CRC0, buf, len, &result);
return result;
}
uint32_t omv_crc32_update(uint32_t crc, const void *buf, size_t len) {
uint32_t result = crc;
if (!crc32_initialized) {
omv_crc32_init();
}
if (len == 0) {
return crc;
}
crc_calculate(CRC0, buf, len, &result);
return result;
}
static void crc_calculate(CRC_Type *crc, const void *buf, uint32_t len, uint32_t *value) {
const uint8_t *data = (const uint8_t *) buf;
uint32_t aligned_len = len & ~3U; // Length aligned to 4 bytes
uint32_t remainder = len & 3U; // Remaining bytes
// Process aligned part (multiple of 4 bytes) with hardware
if (aligned_len > 0) {
crc->CRC_SEED = *value;
crc->CRC_CONTROL |= CRC_INIT_BIT;
const uint32_t *data32 = (const uint32_t *) data;
for (uint32_t i = 0; i < aligned_len / 4; i++) {
crc->CRC_DATA_IN_32_0 = data32[i];
}
*value = crc->CRC_OUT;
}
// Process remaining bytes using software CRC calculation
if (remainder > 0) {
uint32_t result = *value;
const uint8_t *remaining_data = data + aligned_len;
for (uint32_t i = 0; i < remainder; i++) {
result ^= (uint32_t) remaining_data[i] << 24;
for (int bit = 0; bit < 8; bit++) {
if (result & 0x80000000) {
result = (result << 1) ^ OMV_CRC32_POLY;
} else {
result <<= 1;
}
}
}
*value = result;
}
}