Avoid the need for ssize_t.

[zlib.git] / adler32.c

diff --git a/adler32.c b/adler32.c
index 65ad6a5adc44c00428b35eb15ff26d16f9ef209b..3eafddf88fd16c8d6f3efa8e856e633d8d2cde11 100644 (file)
--- a/adler32.c
+++ b/adler32.c
@@ -1,5 +1,5 @@
 /* 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
  */
 
@@ -7,11 +7,9 @@
 
 #include "zutil.h"
 
-#define local static
+local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));
 
-local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2);
-
-#define BASE 65521UL    /* largest prime smaller than 65536 */
+#define BASE 65521U     /* 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 +19,44 @@ 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 +95,7 @@ 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 +140,13 @@ 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);
@@ -146,7 +154,7 @@ local uLong adler32_combine_(adler1, adler2, len2)
     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 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
     if (sum2 >= BASE) sum2 -= BASE;
     return sum1 | (sum2 << 16);
 }