zlib121/adler32.c
changeset 602 691c1eadb8b7
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/zlib121/adler32.c	Sun Dec 07 05:29:20 2003 +0000
@@ -0,0 +1,74 @@
+/* adler32.c -- compute the Adler-32 checksum of a data stream
+ * Copyright (C) 1995-2003 Mark Adler
+ * For conditions of distribution and use, see copyright notice in zlib.h
+ */
+
+/* @(#) $Id: adler32.c,v 1.1 2003/12/07 05:29:20 icculus Exp $ */
+
+#define ZLIB_INTERNAL
+#include "zlib.h"
+
+#define BASE 65521UL    /* largest prime smaller than 65536 */
+#define NMAX 5552
+/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
+
+#define DO1(buf,i)  {s1 += buf[i]; s2 += s1;}
+#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
+#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
+#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
+#define DO16(buf)   DO8(buf,0); DO8(buf,8);
+
+#ifdef NO_DIVIDE
+#  define MOD(a) \
+    do { \
+        if (a >= (BASE << 16)) a -= (BASE << 16); \
+        if (a >= (BASE << 15)) a -= (BASE << 15); \
+        if (a >= (BASE << 14)) a -= (BASE << 14); \
+        if (a >= (BASE << 13)) a -= (BASE << 13); \
+        if (a >= (BASE << 12)) a -= (BASE << 12); \
+        if (a >= (BASE << 11)) a -= (BASE << 11); \
+        if (a >= (BASE << 10)) a -= (BASE << 10); \
+        if (a >= (BASE << 9)) a -= (BASE << 9); \
+        if (a >= (BASE << 8)) a -= (BASE << 8); \
+        if (a >= (BASE << 7)) a -= (BASE << 7); \
+        if (a >= (BASE << 6)) a -= (BASE << 6); \
+        if (a >= (BASE << 5)) a -= (BASE << 5); \
+        if (a >= (BASE << 4)) a -= (BASE << 4); \
+        if (a >= (BASE << 3)) a -= (BASE << 3); \
+        if (a >= (BASE << 2)) a -= (BASE << 2); \
+        if (a >= (BASE << 1)) a -= (BASE << 1); \
+        if (a >= BASE) a -= BASE; \
+    } while (0)
+#else
+#  define MOD(a) a %= BASE
+#endif
+
+/* ========================================================================= */
+uLong ZEXPORT adler32(adler, buf, len)
+    uLong adler;
+    const Bytef *buf;
+    uInt len;
+{
+    unsigned long s1 = adler & 0xffff;
+    unsigned long s2 = (adler >> 16) & 0xffff;
+    int k;
+
+    if (buf == Z_NULL) return 1L;
+
+    while (len > 0) {
+        k = len < NMAX ? (int)len : NMAX;
+        len -= k;
+        while (k >= 16) {
+            DO16(buf);
+            buf += 16;
+            k -= 16;
+        }
+        if (k != 0) do {
+            s1 += *buf++;
+            s2 += s1;
+        } while (--k);
+        MOD(s1);
+        MOD(s2);
+    }
+    return (s2 << 16) | s1;
+}