u8vector-crcs.scm

#|
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|#

;; CRC8 and CRC32 functions for u8vectors

(c-declare  #<<end-of-c-declare

static unsigned char reg=0;

static unsigned char crc8_bytecalc(unsigned char byte){
  int i;
  char flag;
  unsigned char polynom = 0xd5;

  for(i=0; i<8; i++){
    if (reg&0x80){ flag=1; }else{ flag=0; }
    reg <<= 1;
    if (byte&0x80){ reg|=1; }
    byte <<= 1;
    if (flag){ reg ^= polynom; }
  }
  return reg;
}

static unsigned char crc8(unsigned char *data, int len){
  int i;
  reg=0;
  for(i=0; i<len; i++) {
    crc8_bytecalc(data[i]);
  }
  return crc8_bytecalc(0);
}

static unsigned int crctab[256];
#define QUOTIENT 0x04c11db7

static void crc32_init(void){
  int i, j;
  unsigned int crc;
  for (i = 0; i < 256; i++) {
    crc = i << 24;
    for (j = 0; j < 8; j++) {
      if (crc & 0x80000000)
        crc = (crc << 1) ^ QUOTIENT;
      else
        crc = crc << 1;
    }
    crctab[i] = crc;
  }
}

static unsigned int crc32(unsigned char *data, int len){
  unsigned int result;
  int i;
  unsigned char octet;
  if (len < 4) return 0;
  result = *data++ << 24;
  result |= *data++ << 16;
  result |= *data++ << 8;
  result |= *data++;
  result = ~ result;
  len -=4;
  for (i=0; i<len; i++) {
    result = (result << 8 | *data++) ^ crctab[result >> 24];
  }
  return ~result;
}

static unsigned int crc16_ccitt(unsigned char *data, int len){
  int i;
  unsigned short crc=0xffff;
  for (i=0;i<len;i++){
    unsigned short crc_new = (unsigned char)(crc >> 8) | (crc << 8);
    crc_new ^= data[i];
    crc_new ^= (unsigned char)(crc_new & 0xff) >> 4;
    crc_new ^= crc_new << 12;
    crc_new ^= (crc_new & 0xff) << 5;
    crc = crc_new;
  }
  return crc;
}

end-of-c-declare
)

;; initialize the lookup table
(c-initialize "crc32_init();")

(define (u8vector-crc32 v) 
  ((c-lambda (scheme-object int) unsigned-int 
      "___result=crc32(___CAST(void*,___BODY_AS(___arg1,___tSUBTYPED)), ___arg2);")
     v (u8vector-length v)))

(define (u8vector-crc16-ccitt v)
  ((c-lambda (scheme-object int) unsigned-int
     "___result=crc16_ccitt(___CAST(void*,___BODY_AS(___arg1,___tSUBTYPED)), ___arg2);")
     v (u8vector-length v)))

(define (u8vector-crc8 v)
  ((c-lambda (scheme-object int) unsigned-int
      "___result=crc8(___CAST(void*,___BODY_AS(___arg1,___tSUBTYPED)), ___arg2);")
     v (u8vector-length v)))

;; eof