runtime/src/sun/tree/crc32.h

   1 #ifndef SUN_TREE_CRC32_H
   2 #define SUN_TREE_CRC32_H
   3
   4 #include <stdint.h>
   5
   6 #ifdef __cplusplus
   7 extern "C" {
   8 #endif
   9
  10 // Taken from here: https://web.archive.org/web/20190108202303/http://www.hackersdelight.org/hdcodetxt/crc.c.txt
  11 // Licence: https://web.archive.org/web/20190716204559/http://www.hackersdelight.org/permissions.htm
  12 // See also: https://stackoverflow.com/a/21001712
  13 // FIXME: Look into https://gist.github.com/badboy/6267743
  14
  15 uint32_t crc32c(char *message) {
  16    int i, j;
  17    uint32_t byte, crc, mask;
  18    static uint32_t table[256];
  19
  20    /* Set up the table, if necessary. */
  21
  22    if (table[1] == 0) {
  23       for (byte = 0; byte <= 255; byte++) {
  24          crc = byte;
  25          for (j = 7; j >= 0; j--) {    // Do eight times.
  26             mask = -(crc & 1);
  27             crc = (crc >> 1) ^ (0xEDB88320 & mask);
  28          }
  29          table[byte] = crc;
  30       }
  31    }
  32
  33    /* Through with table setup, now calculate the CRC. */
  34
  35    i = 0;
  36    crc = 0xFFFFFFFF;
  37    while ((byte = message[i]) != 0) {
  38       crc = (crc >> 8) ^ table[(crc ^ byte) & 0xFF];
  39       i = i + 1;
  40    }
  41    return ~crc;
  42 }
  43
  44 #ifdef __cplusplus
  45 }
  46 #endif
  47
  48 #endif