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Add CCITT Kermit CRC check for FDX-B demod

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This commit is contained in:
marshmellow42 2015-06-04 12:53:19 -04:00
commit 6eaa8da9dc
3 changed files with 51 additions and 26 deletions
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60
common/crc16.c
View file

@ -11,35 +11,49 @@
unsigned short update_crc16( unsigned short crc, unsigned char c )
{
unsigned short i, v, tcrc = 0;
unsigned short i, v, tcrc = 0;
v = (crc ^ c) & 0xff;
for (i = 0; i < 8; i++) {
tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ 0x8408 : tcrc >> 1;
v >>= 1;
}
v = (crc ^ c) & 0xff;
for (i = 0; i < 8; i++) {
tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ 0x8408 : tcrc >> 1;
v >>= 1;
}
return ((crc >> 8) ^ tcrc)&0xffff;
return ((crc >> 8) ^ tcrc)&0xffff;
}
uint16_t crc16(uint8_t const *message, int length, uint16_t remainder, uint16_t polynomial) {
if (length == 0)
return (~remainder);
for (int byte = 0; byte < length; ++byte) {
remainder ^= (message[byte] << 8);
for (uint8_t bit = 8; bit > 0; --bit) {
if (remainder & 0x8000) {
remainder = (remainder << 1) ^ polynomial;
} else {
remainder = (remainder << 1);
}
}
}
return remainder;
if (length == 0) return (~remainder);
for (int byte = 0; byte < length; ++byte) {
remainder ^= (message[byte] << 8);
for (uint8_t bit = 8; bit > 0; --bit) {
if (remainder & 0x8000) {
remainder = (remainder << 1) ^ polynomial;
} else {
remainder = (remainder << 1);
}
}
}
return remainder;
}
uint16_t crc16_ccitt(uint8_t const *message, int length) {
return crc16(message, length, 0xffff, 0x1021);
return crc16(message, length, 0xffff, 0x1021);
}
uint16_t crc16_ccitt_kermit(uint8_t const *message, int length) {
if (length == 0) return 0;
uint32_t crc = 0, q = 0;
uint8_t c;
for (int i = 0; i < length; i++){
c = message[i];
q = (crc ^ c ) & 0xF;
crc = (crc >> 4) ^ (q * 0x1081);
q = (crc ^ (c >> 4)) & 0xF;
crc = (crc >> 4) ^ (q * 0x1081);
}
return crc;
}

1
common/crc16.h
View file

@ -12,4 +12,5 @@
unsigned short update_crc16(unsigned short crc, unsigned char c);
uint16_t crc16(uint8_t const *message, int length, uint16_t remainder, uint16_t polynomial);
uint16_t crc16_ccitt(uint8_t const *message, int length);
uint16_t crc16_ccitt_kermit(uint8_t const *message, int length);
#endif