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authorjan.nijtmans <nijtmans@users.sourceforge.net>2012-05-03 20:41:22 (GMT)
committerjan.nijtmans <nijtmans@users.sourceforge.net>2012-05-03 20:41:22 (GMT)
commit47d7aa4020e2cd163aeba6435d2a701ad48bee45 (patch)
tree7bd7477b079cef72b27e17b8aad253e764424f27 /compat/zlib/adler32.c
parent8124b5fb585273485814508c23908f35f44d3fba (diff)
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zlib-1.2.7
Diffstat (limited to 'compat/zlib/adler32.c')
-rw-r--r--compat/zlib/adler32.c70
1 files changed, 40 insertions, 30 deletions
diff --git a/compat/zlib/adler32.c b/compat/zlib/adler32.c
index 997020d..a868f07 100644
--- a/compat/zlib/adler32.c
+++ b/compat/zlib/adler32.c
@@ -1,17 +1,17 @@
/* adler32.c -- compute the Adler-32 checksum of a data stream
- * Copyright (C) 1995-2007 Mark Adler
+ * Copyright (C) 1995-2011 Mark Adler
* For conditions of distribution and use, see copyright notice in zlib.h
*/
-/* @(#) $Id: adler32.c,v 1.3 2010/04/20 14:50:10 nijtmans Exp $ */
+/* @(#) $Id$ */
#include "zutil.h"
#define local static
-local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2);
+local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));
-#define BASE 65521UL /* largest prime smaller than 65536 */
+#define BASE 65521 /* 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 */
@@ -21,39 +21,44 @@ local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2);
#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 */
+/* use NO_DIVIDE if your processor does not do division in hardware --
+ try it both ways to see which is faster */
#ifdef NO_DIVIDE
-# define MOD(a) \
+/* note that this assumes BASE is 65521, where 65536 % 65521 == 15
+ (thank you to John Reiser for pointing this out) */
+# define CHOP(a) \
+ do { \
+ unsigned long tmp = a >> 16; \
+ a &= 0xffffUL; \
+ a += (tmp << 4) - tmp; \
+ } while (0)
+# define MOD28(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); \
+ CHOP(a); \
if (a >= BASE) a -= BASE; \
} while (0)
-# define MOD4(a) \
+# define MOD(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); \
+ CHOP(a); \
+ MOD28(a); \
+ } while (0)
+# define MOD63(a) \
+ do { /* this assumes a is not negative */ \
+ z_off64_t tmp = a >> 32; \
+ a &= 0xffffffffL; \
+ a += (tmp << 8) - (tmp << 5) + tmp; \
+ tmp = a >> 16; \
+ a &= 0xffffL; \
+ a += (tmp << 4) - tmp; \
+ tmp = a >> 16; \
+ a &= 0xffffL; \
+ a += (tmp << 4) - tmp; \
if (a >= BASE) a -= BASE; \
} while (0)
#else
# define MOD(a) a %= BASE
-# define MOD4(a) a %= BASE
+# define MOD28(a) a %= BASE
+# define MOD63(a) a %= BASE
#endif
/* ========================================================================= */
@@ -92,7 +97,7 @@ uLong ZEXPORT adler32(adler, buf, len)
}
if (adler >= BASE)
adler -= BASE;
- MOD4(sum2); /* only added so many BASE's */
+ MOD28(sum2); /* only added so many BASE's */
return adler | (sum2 << 16);
}
@@ -137,8 +142,13 @@ local uLong adler32_combine_(adler1, adler2, len2)
unsigned long sum2;
unsigned rem;
+ /* for negative len, return invalid adler32 as a clue for debugging */
+ if (len2 < 0)
+ return 0xffffffffUL;
+
/* the derivation of this formula is left as an exercise for the reader */
- rem = (unsigned)(len2 % BASE);
+ MOD63(len2); /* assumes len2 >= 0 */
+ rem = (unsigned)len2;
sum1 = adler1 & 0xffff;
sum2 = rem * sum1;
MOD(sum2);