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AP_MAth: Move the CRC24 to the AP_Math class

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murata 2020-04-14 19:29:59 +09:00 committed by Andrew Tridgell
parent 4c835a0df9
commit 9714d8dde9
2 changed files with 21 additions and 0 deletions
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20
libraries/AP_Math/crc.cpp
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@ -314,3 +314,23 @@ void hash_fnv_1a(uint32_t len, const uint8_t* buf, uint64_t* hash)
*hash *= FNV_1_PRIME_64; *hash *= FNV_1_PRIME_64;
} }
} }
// calculate 24 bit crc. We take an approach that saves memory and flash at the cost of higher CPU load.
uint32_t crc_crc24(const uint8_t *bytes, uint16_t len)
{
static constexpr uint32_t POLYCRC24 = 0x1864CFB;
uint32_t crc = 0;
while (len--) {
uint8_t b = *bytes++;
const uint8_t idx = (crc>>16) ^ b;
uint32_t crct = idx<<16;
for (uint8_t j=0; j<8; j++) {
crct <<= 1;
if (crct & 0x1000000) {
crct ^= POLYCRC24;
}
}
crc = ((crc<<8)&0xFFFFFF) ^ crct;
}
return crc;
}

1
libraries/AP_Math/crc.h
View File

@ -26,6 +26,7 @@ uint16_t crc_xmodem_update(uint16_t crc, uint8_t data);
uint16_t crc_xmodem(const uint8_t *data, uint16_t len); uint16_t crc_xmodem(const uint8_t *data, uint16_t len);
uint32_t crc_crc32(uint32_t crc, const uint8_t *buf, uint32_t size); uint32_t crc_crc32(uint32_t crc, const uint8_t *buf, uint32_t size);
uint32_t crc32_small(uint32_t crc, const uint8_t *buf, uint32_t size); uint32_t crc32_small(uint32_t crc, const uint8_t *buf, uint32_t size);
uint32_t crc_crc24(const uint8_t *bytes, uint16_t len);
// Copyright (C) 2010 Swift Navigation Inc. // Copyright (C) 2010 Swift Navigation Inc.
// Contact: Fergus Noble <fergus@swift-nav.com> // Contact: Fergus Noble <fergus@swift-nav.com>