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https://github.com/shadps4-emu/ext-zlib-ng.git
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43 lines
908 B
C
43 lines
908 B
C
#ifndef CRC32_BRAID_COMB_P_H_
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#define CRC32_BRAID_COMB_P_H_
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/*
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Return a(x) multiplied by b(x) modulo p(x), where p(x) is the CRC polynomial,
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reflected. For speed, this requires that a not be zero.
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*/
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static uint32_t multmodp(uint32_t a, uint32_t b) {
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uint32_t m, p;
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m = (uint32_t)1 << 31;
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p = 0;
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for (;;) {
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if (a & m) {
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p ^= b;
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if ((a & (m - 1)) == 0)
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break;
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}
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m >>= 1;
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b = b & 1 ? (b >> 1) ^ POLY : b >> 1;
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}
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return p;
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}
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/*
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Return x^(n * 2^k) modulo p(x). Requires that x2n_table[] has been
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initialized.
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*/
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static uint32_t x2nmodp(z_off64_t n, unsigned k) {
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uint32_t p;
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p = (uint32_t)1 << 31; /* x^0 == 1 */
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while (n) {
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if (n & 1)
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p = multmodp(x2n_table[k & 31], p);
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n >>= 1;
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k++;
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}
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return p;
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}
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#endif /* CRC32_BRAID_COMB_P_H_ */
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