crccache/crccache.c

   1 /*
   2  * crccache.c
   3  *
   4  *  Created on: 22/02/2009
   5  *      Author: Toby Collett
   6  */
   7
   8 #include <string.h>
   9 #include <apr_base64.h>
  10
  11 /* fills in the first 5 bytes of target with the base64 bit encoded hash
  12
  13 it is endian safe, and adds a null terminator, so target must have space for 6 bytes
  14 */
  15 char * encode_30bithash(unsigned hash, char * target)
  16 {
  17         char temp_result[9];
  18         unsigned char source[4];
  19         // possibly a faster way, but needs to be endian safe, including bit endianness
  20         source[0]=(hash&0x3fc00000)>>22;
  21         source[1]=(hash&0x003fc000)>>14;
  22         source[2]=(hash&0x00003fc0)>>6;
  23         source[3]=(hash&0x0000003f)<<2;
  24
  25         apr_base64_encode (temp_result, (void *)source, 4);
  26         memcpy(target,temp_result,5);
  27         target[5]='\0';
  28         return target;
  29 }
  30
  31
  32 /* decodes a 5 bytes base 64bit string to the lower 30 bits of an int
  33
  34 it is endian safe, and assumes an input string of 5 bytes
  35 */
  36 unsigned decode_30bithash(const char * source)
  37 {
  38         char temp_source[6];
  39         unsigned char target[7];
  40         memcpy(temp_source,source,5);
  41         temp_source[5]='0';
  42         temp_source[6]='0';
  43         temp_source[7]='0';
  44         temp_source[8]='\0';
  45
  46         apr_base64_decode ((void*)target, temp_source);
  47         unsigned result;
  48         result  = target[0] << 22;
  49         result |= target[1] << 14;
  50         result |= target[2] << 6;
  51         result |= target[3] >> 2;
  52
  53         return result;
  54 }