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55 lines
1.6 KiB
C
55 lines
1.6 KiB
C
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/* adler32.c -- compute the Adler-32 checksum of a data stream
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* Copyright (C) 1995-2011, 2016 Mark Adler
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* For conditions of distribution and use, see copyright notice in zlib.h
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*/
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#include "zbuild.h"
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#include "functable.h"
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#include "adler32_p.h"
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/* ========================================================================= */
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Z_INTERNAL uint32_t adler32_c(uint32_t adler, const uint8_t *buf, size_t len) {
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uint32_t sum2;
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unsigned n;
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/* split Adler-32 into component sums */
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sum2 = (adler >> 16) & 0xffff;
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adler &= 0xffff;
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/* in case user likes doing a byte at a time, keep it fast */
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if (UNLIKELY(len == 1))
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return adler32_len_1(adler, buf, sum2);
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/* initial Adler-32 value (deferred check for len == 1 speed) */
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if (UNLIKELY(buf == NULL))
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return 1L;
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/* in case short lengths are provided, keep it somewhat fast */
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if (UNLIKELY(len < 16))
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return adler32_len_16(adler, buf, len, sum2);
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/* do length NMAX blocks -- requires just one modulo operation */
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while (len >= NMAX) {
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len -= NMAX;
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#ifdef UNROLL_MORE
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n = NMAX / 16; /* NMAX is divisible by 16 */
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#else
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n = NMAX / 8; /* NMAX is divisible by 8 */
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#endif
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do {
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#ifdef UNROLL_MORE
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DO16(adler, sum2, buf); /* 16 sums unrolled */
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buf += 16;
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#else
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DO8(adler, sum2, buf, 0); /* 8 sums unrolled */
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buf += 8;
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#endif
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} while (--n);
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adler %= BASE;
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sum2 %= BASE;
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}
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/* do remaining bytes (less than NMAX, still just one modulo) */
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return adler32_len_64(adler, buf, len, sum2);
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}
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