compression/zlib/adler32.c

0001 /* adler32.c -- compute the Adler-32 checksum of a data stream
0002  * Copyright (C) 1995-2011, 2016 Mark Adler
0003  * For conditions of distribution and use, see copyright notice in zlib.h
0004  */
0005
0006 /* @(#) $Id$ */
0007
0008 #include "zutil.h"
0009
0010 local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));
0011
0012 #define BASE 65521U     /* largest prime smaller than 65536 */
0013 #define NMAX 5552
0014 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
0015
0016 #define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
0017 #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
0018 #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
0019 #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
0020 #define DO16(buf)   DO8(buf,0); DO8(buf,8);
0021
0022 /* use NO_DIVIDE if your processor does not do division in hardware --
0023    try it both ways to see which is faster */
0024 #ifdef NO_DIVIDE
0025 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
0026    (thank you to John Reiser for pointing this out) */
0027 #  define CHOP(a) \
0028     do { \
0029         unsigned long tmp = a >> 16; \
0030         a &= 0xffffUL; \
0031         a += (tmp << 4) - tmp; \
0032     } while (0)
0033 #  define MOD28(a) \
0034     do { \
0035         CHOP(a); \
0036         if (a >= BASE) a -= BASE; \
0037     } while (0)
0038 #  define MOD(a) \
0039     do { \
0040         CHOP(a); \
0041         MOD28(a); \
0042     } while (0)
0043 #  define MOD63(a) \
0044     do { /* this assumes a is not negative */ \
0045         z_off64_t tmp = a >> 32; \
0046         a &= 0xffffffffL; \
0047         a += (tmp << 8) - (tmp << 5) + tmp; \
0048         tmp = a >> 16; \
0049         a &= 0xffffL; \
0050         a += (tmp << 4) - tmp; \
0051         tmp = a >> 16; \
0052         a &= 0xffffL; \
0053         a += (tmp << 4) - tmp; \
0054         if (a >= BASE) a -= BASE; \
0055     } while (0)
0056 #else
0057 #  define MOD(a) a %= BASE
0058 #  define MOD28(a) a %= BASE
0059 #  define MOD63(a) a %= BASE
0060 #endif
0061
0062 /* ========================================================================= */
0063 uLong ZEXPORT adler32_z(adler, buf, len)
0064     uLong adler;
0065     const Bytef *buf;
0066     z_size_t len;
0067 {
0068     unsigned long sum2;
0069     unsigned n;
0070
0071     /* split Adler-32 into component sums */
0072     sum2 = (adler >> 16) & 0xffff;
0073     adler &= 0xffff;
0074
0075     /* in case user likes doing a byte at a time, keep it fast */
0076     if (len == 1) {
0077         adler += buf[0];
0078         if (adler >= BASE)
0079             adler -= BASE;
0080         sum2 += adler;
0081         if (sum2 >= BASE)
0082             sum2 -= BASE;
0083         return adler | (sum2 << 16);
0084     }
0085
0086     /* initial Adler-32 value (deferred check for len == 1 speed) */
0087     if (buf == Z_NULL)
0088         return 1L;
0089
0090     /* in case short lengths are provided, keep it somewhat fast */
0091     if (len < 16) {
0092         while (len--) {
0093             adler += *buf++;
0094             sum2 += adler;
0095         }
0096         if (adler >= BASE)
0097             adler -= BASE;
0098         MOD28(sum2);            /* only added so many BASE's */
0099         return adler | (sum2 << 16);
0100     }
0101
0102     /* do length NMAX blocks -- requires just one modulo operation */
0103     while (len >= NMAX) {
0104         len -= NMAX;
0105         n = NMAX / 16;          /* NMAX is divisible by 16 */
0106         do {
0107             DO16(buf);          /* 16 sums unrolled */
0108             buf += 16;
0109         } while (--n);
0110         MOD(adler);
0111         MOD(sum2);
0112     }
0113
0114     /* do remaining bytes (less than NMAX, still just one modulo) */
0115     if (len) {                  /* avoid modulos if none remaining */
0116         while (len >= 16) {
0117             len -= 16;
0118             DO16(buf);
0119             buf += 16;
0120         }
0121         while (len--) {
0122             adler += *buf++;
0123             sum2 += adler;
0124         }
0125         MOD(adler);
0126         MOD(sum2);
0127     }
0128
0129     /* return recombined sums */
0130     return adler | (sum2 << 16);
0131 }
0132
0133 /* ========================================================================= */
0134 uLong ZEXPORT adler32(adler, buf, len)
0135     uLong adler;
0136     const Bytef *buf;
0137     uInt len;
0138 {
0139     return adler32_z(adler, buf, len);
0140 }
0141
0142 /* ========================================================================= */
0143 local uLong adler32_combine_(adler1, adler2, len2)
0144     uLong adler1;
0145     uLong adler2;
0146     z_off64_t len2;
0147 {
0148     unsigned long sum1;
0149     unsigned long sum2;
0150     unsigned rem;
0151
0152     /* for negative len, return invalid adler32 as a clue for debugging */
0153     if (len2 < 0)
0154         return 0xffffffffUL;
0155
0156     /* the derivation of this formula is left as an exercise for the reader */
0157     MOD63(len2);                /* assumes len2 >= 0 */
0158     rem = (unsigned)len2;
0159     sum1 = adler1 & 0xffff;
0160     sum2 = rem * sum1;
0161     MOD(sum2);
0162     sum1 += (adler2 & 0xffff) + BASE - 1;
0163     sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
0164     if (sum1 >= BASE) sum1 -= BASE;
0165     if (sum1 >= BASE) sum1 -= BASE;
0166     if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
0167     if (sum2 >= BASE) sum2 -= BASE;
0168     return sum1 | (sum2 << 16);
0169 }
0170
0171 /* ========================================================================= */
0172 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
0173     uLong adler1;
0174     uLong adler2;
0175     z_off_t len2;
0176 {
0177     return adler32_combine_(adler1, adler2, len2);
0178 }
0179
0180 uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
0181     uLong adler1;
0182     uLong adler2;
0183     z_off64_t len2;
0184 {
0185     return adler32_combine_(adler1, adler2, len2);
0186 }