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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 #include "zlib.h" #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(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); }