/* adler32.c -- compute the Adler-32 checksum of a data stream
- * Copyright (C) 1995-1998 Mark Adler
- * For conditions of distribution and use, see copyright notice in zlib.h
+ * Copyright (C) 1995-2004 Mark Adler
+ * For conditions of distribution and use, see copyright notice in zlib.h
*/
-/* @(#) $Id$ */
+/* @(#) $Id: adler32.c,v 1.1.1.2 2002/03/11 21:53:23 tromey Exp $ */
+#define ZLIB_INTERNAL
#include "zlib.h"
-#define BASE 65521L /* largest prime smaller than 65536 */
+#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 DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
#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);
+/* use NO_DIVIDE if your processor does not do division in hardware */
+#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)
+# define MOD4(a) \
+ do { \
+ 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
+# define MOD4(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;
+ unsigned long sum2;
+ unsigned n;
+
+ /* split Adler-32 into component sums */
+ sum2 = (adler >> 16) & 0xffff;
+ adler &= 0xffff;
+
+ /* in case user likes doing a byte at a time, keep it fast */
+ if (len == 1) {
+ adler += buf[0];
+ if (adler >= BASE)
+ adler -= BASE;
+ sum2 += adler;
+ if (sum2 >= BASE)
+ sum2 -= BASE;
+ return adler | (sum2 << 16);
+ }
+
+ /* initial Adler-32 value (deferred check for len == 1 speed) */
+ if (buf == Z_NULL)
+ return 1L;
+
+ /* in case short lengths are provided, keep it somewhat fast */
+ if (len < 16) {
+ while (len--) {
+ adler += *buf++;
+ sum2 += adler;
+ }
+ if (adler >= BASE)
+ adler -= BASE;
+ MOD4(sum2); /* only added so many BASE's */
+ return adler | (sum2 << 16);
+ }
- if (buf == Z_NULL) return 1L;
+ /* do length NMAX blocks -- requires just one modulo operation */
+ while (len >= NMAX) {
+ len -= NMAX;
+ n = NMAX / 16; /* NMAX is divisible by 16 */
+ do {
+ DO16(buf); /* 16 sums unrolled */
+ buf += 16;
+ } while (--n);
+ MOD(adler);
+ MOD(sum2);
+ }
- while (len > 0) {
- k = len < NMAX ? len : NMAX;
- len -= k;
- while (k >= 16) {
+ /* do remaining bytes (less than NMAX, still just one modulo) */
+ if (len) { /* avoid modulos if none remaining */
+ while (len >= 16) {
+ len -= 16;
DO16(buf);
- buf += 16;
- k -= 16;
+ buf += 16;
+ }
+ while (len--) {
+ adler += *buf++;
+ sum2 += adler;
}
- if (k != 0) do {
- s1 += *buf++;
- s2 += s1;
- } while (--k);
- s1 %= BASE;
- s2 %= BASE;
+ MOD(adler);
+ MOD(sum2);
}
- return (s2 << 16) | s1;
+
+ /* return recombined sums */
+ return adler | (sum2 << 16);
+}
+
+/* ========================================================================= */
+uLong ZEXPORT adler32_combine(adler1, adler2, len2)
+ uLong adler1;
+ uLong adler2;
+ z_off_t len2;
+{
+ unsigned long sum1;
+ unsigned long sum2;
+ unsigned rem;
+
+ /* the derivation of this formula is left as an exercise for the reader */
+ rem = (unsigned)(len2 % BASE);
+ sum1 = adler1 & 0xffff;
+ sum2 = rem * sum1;
+ MOD(sum2);
+ sum1 += (adler2 & 0xffff) + BASE - 1;
+ sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
+ if (sum1 > BASE) sum1 -= BASE;
+ if (sum1 > BASE) sum1 -= BASE;
+ if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
+ if (sum2 > BASE) sum2 -= BASE;
+ return sum1 | (sum2 << 16);
}
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