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47 lines
1.7 KiB
C
47 lines
1.7 KiB
C
#if 0
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/*─────────────────────────────────────────────────────────────────╗
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│ To the extent possible under law, Justine Tunney has waived │
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│ all copyright and related or neighboring rights to this file, │
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│ as it is written in the following disclaimers: │
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│ • http://unlicense.org/ │
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│ • http://creativecommons.org/publicdomain/zero/1.0/ │
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╚─────────────────────────────────────────────────────────────────*/
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#endif
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#include "libc/stdio/stdio.h"
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#include "libc/testlib/ezbench.h"
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/**
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* @fileoverview Fast Modulus Using Multiplication Tutorial
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*
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* Expected program output:
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*
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* 23 / 3 = 7
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* 0x5555555555555556 1 1
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* modulus l: 15𝑐 5𝑛𝑠
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* fastmod l: 4𝑐 1𝑛𝑠
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* precomp l: 18𝑐 6𝑛𝑠
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*/
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struct Modulus {
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uint64_t c;
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uint64_t d;
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};
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struct Modulus GetModulus(uint64_t d) {
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return (struct Modulus){0xFFFFFFFFFFFFFFFFull / d + 1, d};
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}
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uint64_t Modulus(uint64_t x, struct Modulus m) {
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return ((uint128_t)(m.c * x) * m.d) >> 64;
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}
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int main(int argc, char *argv[]) {
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printf("%#lx %% %d = %d\n", 0x23, 3, Modulus(23, GetModulus(3)));
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printf("%#lx %% %d = %d\n", 0x123, 17, Modulus(0x123, GetModulus(17)));
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volatile struct Modulus v = GetModulus(3);
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volatile uint64_t x = 23, y = 3, z;
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EZBENCH2("modulus", donothing, z = x % y);
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EZBENCH2("fastmod", donothing, z = Modulus(x, v));
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EZBENCH2("precomp", donothing, v = GetModulus(y));
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return 0;
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}
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