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crc32.c

#include "Platform.h"
#include "exehead/config.h"
#ifdef NSIS_CONFIG_CRC_SUPPORT

// this is based on the (slow,small) CRC32 implementation from zlib.
unsigned long NSISCALL CRC32(unsigned long crc, const unsigned char *buf, unsigned int len)
{
    static unsigned long crc_table[256];

    if (!crc_table[1])
    {
      unsigned long c;
      int n, k;

      for (n = 0; n < 256; n++)
      {
        c = (unsigned long)n;
        for (k = 0; k < 8; k++) c = (c >> 1) ^ (c & 1 ? 0xedb88320L : 0);
        crc_table[n] = c;
      }
    }

    crc = crc ^ 0xffffffffL;
    while (len-- > 0) {
      crc = crc_table[(crc ^ (*buf++)) & 0xff] ^ (crc >> 8);
    }
    return crc ^ 0xffffffffL;
}

#endif

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