| /* adler32.c -- compute the Adler-32 checksum of a data stream |
| * Copyright (C) 1995-2011, 2016 Mark Adler |
| * For conditions of distribution and use, see copyright notice in zlib.h |
| */ |
| |
| /* @(#) $Id$ */ |
| |
| #include "zutil.h" |
| |
| #ifndef Z_FREETYPE |
| local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2)); |
| #endif |
| |
| #define BASE 65521U /* 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 -- |
| try it both ways to see which is faster */ |
| #ifdef NO_DIVIDE |
| /* note that this assumes BASE is 65521, where 65536 % 65521 == 15 |
| (thank you to John Reiser for pointing this out) */ |
| # define CHOP(a) \ |
| do { \ |
| unsigned long tmp = a >> 16; \ |
| a &= 0xffffUL; \ |
| a += (tmp << 4) - tmp; \ |
| } while (0) |
| # define MOD28(a) \ |
| do { \ |
| CHOP(a); \ |
| if (a >= BASE) a -= BASE; \ |
| } while (0) |
| # define MOD(a) \ |
| do { \ |
| CHOP(a); \ |
| MOD28(a); \ |
| } while (0) |
| # define MOD63(a) \ |
| do { /* this assumes a is not negative */ \ |
| z_off64_t tmp = a >> 32; \ |
| a &= 0xffffffffL; \ |
| a += (tmp << 8) - (tmp << 5) + tmp; \ |
| tmp = a >> 16; \ |
| a &= 0xffffL; \ |
| a += (tmp << 4) - tmp; \ |
| tmp = a >> 16; \ |
| a &= 0xffffL; \ |
| a += (tmp << 4) - tmp; \ |
| if (a >= BASE) a -= BASE; \ |
| } while (0) |
| #else |
| # define MOD(a) a %= BASE |
| # define MOD28(a) a %= BASE |
| # define MOD63(a) a %= BASE |
| #endif |
| |
| /* ========================================================================= */ |
| uLong ZEXPORT adler32_z( |
| uLong adler, |
| const Bytef *buf, |
| z_size_t 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; |
| MOD28(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( |
| uLong adler, |
| const Bytef *buf, |
| uInt len) |
| { |
| return adler32_z(adler, buf, len); |
| } |
| |
| #ifndef Z_FREETYPE |
| |
| /* ========================================================================= */ |
| local uLong adler32_combine_( |
| uLong adler1, |
| uLong adler2, |
| z_off64_t len2) |
| { |
| unsigned long sum1; |
| unsigned long sum2; |
| unsigned rem; |
| |
| /* for negative len, return invalid adler32 as a clue for debugging */ |
| if (len2 < 0) |
| return 0xffffffffUL; |
| |
| /* the derivation of this formula is left as an exercise for the reader */ |
| MOD63(len2); /* assumes len2 >= 0 */ |
| rem = (unsigned)len2; |
| 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 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1); |
| if (sum2 >= BASE) sum2 -= BASE; |
| return sum1 | (sum2 << 16); |
| } |
| |
| /* ========================================================================= */ |
| uLong ZEXPORT adler32_combine( |
| uLong adler1, |
| uLong adler2, |
| z_off_t len2) |
| { |
| return adler32_combine_(adler1, adler2, len2); |
| } |
| |
| uLong ZEXPORT adler32_combine64( |
| uLong adler1, |
| uLong adler2, |
| z_off64_t len2) |
| { |
| return adler32_combine_(adler1, adler2, len2); |
| } |
| |
| #endif /* !Z_FREETYPE */ |