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78 lines
2.1 KiB
C++
78 lines
2.1 KiB
C++
/* adler32_p.h -- Private inline functions and macros shared with
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* different computation of the Adler-32 checksum
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* 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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#ifndef ADLER32_P_H
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#define ADLER32_P_H
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#define BASE 65521U /* largest prime smaller than 65536 */
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#define NMAX 5552
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/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
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/* use NO_DIVIDE if your processor does not do division in hardware --
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try it both ways to see which is faster */
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#ifdef NO_DIVIDE
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/* note that this assumes BASE is 65521, where 65536 % 65521 == 15
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(thank you to John Reiser for pointing this out) */
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# define CHOP(a) \
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do { \
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uint32_t tmp = a >> 16; \
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a &= 0xffff; \
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a += (tmp << 4) - tmp; \
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} while (0)
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# define MOD28(a) \
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do { \
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CHOP(a); \
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if (a >= BASE) a -= BASE; \
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} while (0)
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# define MOD(a) \
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do { \
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CHOP(a); \
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MOD28(a); \
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} while (0)
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# define MOD63(a) \
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do { /* this assumes a is not negative */ \
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z_off64_t tmp = a >> 32; \
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a &= 0xffffffffL; \
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a += (tmp << 8) - (tmp << 5) + tmp; \
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tmp = a >> 16; \
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a &= 0xffffL; \
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a += (tmp << 4) - tmp; \
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tmp = a >> 16; \
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a &= 0xffffL; \
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a += (tmp << 4) - tmp; \
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if (a >= BASE) a -= BASE; \
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} while (0)
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#else
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# define MOD(a) a %= BASE
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# define MOD28(a) a %= BASE
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# define MOD63(a) a %= BASE
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#endif
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static inline uint32_t adler32_len_1(uint32_t adler, const unsigned char *buf, uint32_t sum2) {
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adler += buf[0];
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if (adler >= BASE)
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adler -= BASE;
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sum2 += adler;
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if (sum2 >= BASE)
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sum2 -= BASE;
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return adler | (sum2 << 16);
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}
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static inline uint32_t adler32_len_16(uint32_t adler, const unsigned char *buf, size_t len, uint32_t sum2) {
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while (len) {
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--len;
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adler += *buf++;
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sum2 += adler;
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}
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if (adler >= BASE)
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adler -= BASE;
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MOD28(sum2); /* only added so many BASE's */
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return adler | (sum2 << 16);
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}
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#endif /* ADLER32_P_H */
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