FreeBSD/Linux Kernel Cross Reference
sys/libkern/zlib/adler32.c

     /*
      * Copyright (c) 2008 Apple Inc. All rights reserved.
      *
      * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
      * 
      * This file contains Original Code and/or Modifications of Original Code
      * as defined in and that are subject to the Apple Public Source License
      * Version 2.0 (the 'License'). You may not use this file except in
      * compliance with the License. The rights granted to you under the License
     * may not be used to create, or enable the creation or redistribution of,
     * unlawful or unlicensed copies of an Apple operating system, or to
     * circumvent, violate, or enable the circumvention or violation of, any
     * terms of an Apple operating system software license agreement.
     * 
     * Please obtain a copy of the License at
     * http://www.opensource.apple.com/apsl/ and read it before using this file.
     * 
     * The Original Code and all software distributed under the License are
     * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
     * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
     * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
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     * Please see the License for the specific language governing rights and
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     */
    /* adler32.c -- compute the Adler-32 checksum of a data stream
     * Copyright (C) 1995-2004 Mark Adler
     * For conditions of distribution and use, see copyright notice in zlib.h
     */
    
    /* @(#) $Id$ */
    
    #define ZLIB_INTERNAL
    #if KERNEL
        #include <libkern/zlib.h>
    #else
        #include "zlib.h"
    #endif /* KERNEL */
    
    #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)  {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 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);
       }
   
       /* 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);
       }
   
       /* 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;
           }
           while (len--) {
               adler += *buf++;
               sum2 += adler;
           }
           MOD(adler);
           MOD(sum2);
       }
   
       /* 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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