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AP_Math: add CRC crc16_ccitt_r function

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jfbblue0922 2023-10-26 16:55:03 +09:00 committed by Peter Barker
parent 2e5af08a10
commit c17907cadc
2 changed files with 21 additions and 0 deletions
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20
libraries/AP_Math/crc.cpp
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@ -384,6 +384,26 @@ uint16_t crc16_ccitt(const uint8_t *buf, uint32_t len, uint16_t crc)
return crc; return crc;
} }
// CRC16_CCITT algorithm using right shift
uint16_t crc16_ccitt_r(const uint8_t *buf, uint32_t len, uint16_t crc, uint16_t out)
{
for (uint32_t i = 0; i < len; i++) {
crc ^= *buf++; // XOR byte into least sig. byte of crc
for (uint8_t j = 0; j < 8; j++) { // loop over each bit
if ((crc & 0x0001) != 0) { // if the LSB is set
crc >>= 1; // shift right and XOR 0x8408
crc ^= 0x8408;
} else {
crc >>= 1; // just shift right
}
}
}
// output xor
crc = crc ^ out;
return crc;
}
uint16_t crc16_ccitt_GDL90(const uint8_t *buf, uint32_t len, uint16_t crc) uint16_t crc16_ccitt_GDL90(const uint8_t *buf, uint32_t len, uint16_t crc)
{ {
for (uint32_t i = 0; i < len; i++) { for (uint32_t i = 0; i < len; i++) {

1
libraries/AP_Math/crc.h
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@ -41,6 +41,7 @@ uint8_t crc_sum8(const uint8_t *p, uint8_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>
uint16_t crc16_ccitt(const uint8_t *buf, uint32_t len, uint16_t crc); uint16_t crc16_ccitt(const uint8_t *buf, uint32_t len, uint16_t crc);
uint16_t crc16_ccitt_r(const uint8_t *buf, uint32_t len, uint16_t crc, uint16_t out);
// CRC16_CCITT algorithm using the GDL90 parser method which is non-standard // CRC16_CCITT algorithm using the GDL90 parser method which is non-standard
// https://www.faa.gov/nextgen/programs/adsb/archival/media/gdl90_public_icd_reva.pdf // https://www.faa.gov/nextgen/programs/adsb/archival/media/gdl90_public_icd_reva.pdf