--- /dev/null
+/* adler32.c -- compute the Adler-32 checksum of a data stream\r
+ * Copyright (C) 1995-2011 Mark Adler\r
+ * For conditions of distribution and use, see copyright notice in zlib.h\r
+ */\r
+\r
+/* @(#) $Id$ */\r
+\r
+#include "zutil.h"\r
+\r
+#define local static\r
+\r
+local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));\r
+\r
+#define BASE 65521 /* largest prime smaller than 65536 */\r
+#define NMAX 5552\r
+/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */\r
+\r
+#define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}\r
+#define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);\r
+#define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);\r
+#define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);\r
+#define DO16(buf) DO8(buf,0); DO8(buf,8);\r
+\r
+/* use NO_DIVIDE if your processor does not do division in hardware --\r
+ try it both ways to see which is faster */\r
+#ifdef NO_DIVIDE\r
+/* note that this assumes BASE is 65521, where 65536 % 65521 == 15\r
+ (thank you to John Reiser for pointing this out) */\r
+# define CHOP(a) \\r
+ do { \\r
+ unsigned long tmp = a >> 16; \\r
+ a &= 0xffffUL; \\r
+ a += (tmp << 4) - tmp; \\r
+ } while (0)\r
+# define MOD28(a) \\r
+ do { \\r
+ CHOP(a); \\r
+ if (a >= BASE) a -= BASE; \\r
+ } while (0)\r
+# define MOD(a) \\r
+ do { \\r
+ CHOP(a); \\r
+ MOD28(a); \\r
+ } while (0)\r
+# define MOD63(a) \\r
+ do { /* this assumes a is not negative */ \\r
+ z_off64_t tmp = a >> 32; \\r
+ a &= 0xffffffffL; \\r
+ a += (tmp << 8) - (tmp << 5) + tmp; \\r
+ tmp = a >> 16; \\r
+ a &= 0xffffL; \\r
+ a += (tmp << 4) - tmp; \\r
+ tmp = a >> 16; \\r
+ a &= 0xffffL; \\r
+ a += (tmp << 4) - tmp; \\r
+ if (a >= BASE) a -= BASE; \\r
+ } while (0)\r
+#else\r
+# define MOD(a) a %= BASE\r
+# define MOD28(a) a %= BASE\r
+# define MOD63(a) a %= BASE\r
+#endif\r
+\r
+/* ========================================================================= */\r
+uLong ZEXPORT adler32(adler, buf, len)\r
+ uLong adler;\r
+ const Bytef *buf;\r
+ uInt len;\r
+{\r
+ unsigned long sum2;\r
+ unsigned n;\r
+\r
+ /* split Adler-32 into component sums */\r
+ sum2 = (adler >> 16) & 0xffff;\r
+ adler &= 0xffff;\r
+\r
+ /* in case user likes doing a byte at a time, keep it fast */\r
+ if (len == 1) {\r
+ adler += buf[0];\r
+ if (adler >= BASE)\r
+ adler -= BASE;\r
+ sum2 += adler;\r
+ if (sum2 >= BASE)\r
+ sum2 -= BASE;\r
+ return adler | (sum2 << 16);\r
+ }\r
+\r
+ /* initial Adler-32 value (deferred check for len == 1 speed) */\r
+ if (buf == Z_NULL)\r
+ return 1L;\r
+\r
+ /* in case short lengths are provided, keep it somewhat fast */\r
+ if (len < 16) {\r
+ while (len--) {\r
+ adler += *buf++;\r
+ sum2 += adler;\r
+ }\r
+ if (adler >= BASE)\r
+ adler -= BASE;\r
+ MOD28(sum2); /* only added so many BASE's */\r
+ return adler | (sum2 << 16);\r
+ }\r
+\r
+ /* do length NMAX blocks -- requires just one modulo operation */\r
+ while (len >= NMAX) {\r
+ len -= NMAX;\r
+ n = NMAX / 16; /* NMAX is divisible by 16 */\r
+ do {\r
+ DO16(buf); /* 16 sums unrolled */\r
+ buf += 16;\r
+ } while (--n);\r
+ MOD(adler);\r
+ MOD(sum2);\r
+ }\r
+\r
+ /* do remaining bytes (less than NMAX, still just one modulo) */\r
+ if (len) { /* avoid modulos if none remaining */\r
+ while (len >= 16) {\r
+ len -= 16;\r
+ DO16(buf);\r
+ buf += 16;\r
+ }\r
+ while (len--) {\r
+ adler += *buf++;\r
+ sum2 += adler;\r
+ }\r
+ MOD(adler);\r
+ MOD(sum2);\r
+ }\r
+\r
+ /* return recombined sums */\r
+ return adler | (sum2 << 16);\r
+}\r
+\r
+/* ========================================================================= */\r
+local uLong adler32_combine_(adler1, adler2, len2)\r
+ uLong adler1;\r
+ uLong adler2;\r
+ z_off64_t len2;\r
+{\r
+ unsigned long sum1;\r
+ unsigned long sum2;\r
+ unsigned rem;\r
+\r
+ /* for negative len, return invalid adler32 as a clue for debugging */\r
+ if (len2 < 0)\r
+ return 0xffffffffUL;\r
+\r
+ /* the derivation of this formula is left as an exercise for the reader */\r
+ MOD63(len2); /* assumes len2 >= 0 */\r
+ rem = (unsigned)len2;\r
+ sum1 = adler1 & 0xffff;\r
+ sum2 = rem * sum1;\r
+ MOD(sum2);\r
+ sum1 += (adler2 & 0xffff) + BASE - 1;\r
+ sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;\r
+ if (sum1 >= BASE) sum1 -= BASE;\r
+ if (sum1 >= BASE) sum1 -= BASE;\r
+ if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);\r
+ if (sum2 >= BASE) sum2 -= BASE;\r
+ return sum1 | (sum2 << 16);\r
+}\r
+\r
+/* ========================================================================= */\r
+uLong ZEXPORT adler32_combine(adler1, adler2, len2)\r
+ uLong adler1;\r
+ uLong adler2;\r
+ z_off_t len2;\r
+{\r
+ return adler32_combine_(adler1, adler2, len2);\r
+}\r
+\r
+uLong ZEXPORT adler32_combine64(adler1, adler2, len2)\r
+ uLong adler1;\r
+ uLong adler2;\r
+ z_off64_t len2;\r
+{\r
+ return adler32_combine_(adler1, adler2, len2);\r
+}\r
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