diff options
Diffstat (limited to 'libpng/adler32.c')
| -rw-r--r-- | libpng/adler32.c | 148 |
1 files changed, 126 insertions, 22 deletions
diff --git a/libpng/adler32.c b/libpng/adler32.c index 8990fd6..007ba26 100644 --- a/libpng/adler32.c +++ b/libpng/adler32.c @@ -1,45 +1,149 @@ /* adler32.c -- compute the Adler-32 checksum of a data stream - * Copyright (C) 1995-2002 Mark Adler - * For conditions of distribution and use, see copyright notice in zlib.h + * 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 65521L /* largest prime smaller than 65536 */ +#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) {s1 += buf[i]; s2 += s1;} +#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) +uLong ZEXPORT adler32(adler, buf, len) + uLong adler; + const Bytef *buf; + uInt len; { - unsigned long s1 = adler & 0xffff; - unsigned long s2 = (adler >> 16) & 0xffff; - int k; + 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); + } - if (buf == Z_NULL) return 1L; + /* 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); + } - while (len > 0) { - k = len < NMAX ? len : NMAX; - len -= k; - while (k >= 16) { + /* 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; - k -= 16; + buf += 16; + } + while (len--) { + adler += *buf++; + sum2 += adler; } - if (k != 0) do { - s1 += *buf++; - s2 += s1; - } while (--k); - s1 %= BASE; - s2 %= BASE; + MOD(adler); + MOD(sum2); } - return (s2 << 16) | s1; + + /* 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); } |