crnlib/crn_checksum.cpp

@@ -0,0 +1,63 @@
+// File: crn_checksum.cpp
+#include "crn_core.h"
+
+namespace crnlib
+{
+   // From the public domain stb.h header.
+   uint adler32(const void* pBuf, size_t buflen, uint adler32)
+   {
+      const uint8* buffer = static_cast<const uint8*>(pBuf);
+      
+      const unsigned long ADLER_MOD = 65521;
+      unsigned long s1 = adler32 & 0xffff, s2 = adler32 >> 16;
+      size_t blocklen;
+      unsigned long i;
+
+      blocklen = buflen % 5552;
+      while (buflen) {
+         for (i=0; i + 7 < blocklen; i += 8) {
+            s1 += buffer[0], s2 += s1;
+            s1 += buffer[1], s2 += s1;
+            s1 += buffer[2], s2 += s1;
+            s1 += buffer[3], s2 += s1;
+            s1 += buffer[4], s2 += s1;
+            s1 += buffer[5], s2 += s1;
+            s1 += buffer[6], s2 += s1;
+            s1 += buffer[7], s2 += s1;
+
+            buffer += 8;
+         }
+
+         for (; i < blocklen; ++i)
+            s1 += *buffer++, s2 += s1;
+
+         s1 %= ADLER_MOD, s2 %= ADLER_MOD;
+         buflen -= blocklen;
+         blocklen = 5552;
+      }
+      return (s2 << 16) + s1;
+   }
+   
+   uint16 crc16(const void* pBuf, size_t len, uint16 crc)
+   {
+      crc = ~crc;
+
+      const uint8* p = reinterpret_cast<const uint8*>(pBuf);
+      while (len)
+      {
+         const uint16 q = *p++ ^ (crc >> 8);
+         crc <<= 8U;
+         uint16 r = (q >> 4) ^ q;
+         crc ^= r;
+         r <<= 5U;
+         crc ^= r;
+         r <<= 7U;
+         crc ^= r; 
+         len--;
+      }
+
+      return static_cast<uint16>(~crc);
+   }
+
+} // namespace crnlib
+