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76 lines
1.7 KiB
76 lines
1.7 KiB
#pragma once
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#include <stdint.h>
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#include <stddef.h>
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namespace gp {
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namespace math {
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template<typename word_t>
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size_t log2(word_t v);
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/**
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Sean Eron Anderson
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seander@cs.stanford.edu
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**/
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template<>
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constexpr size_t log2<uint32_t>(uint32_t v)
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{
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constexpr int MultiplyDeBruijnBitPosition[32] =
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{
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0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
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8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
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};
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v |= v >> 1;
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v |= v >> 2;
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v |= v >> 4;
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v |= v >> 8;
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v |= v >> 16;
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return MultiplyDeBruijnBitPosition[(uint32_t)(v * 0x07C4ACDDU) >> 27];
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}
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template<>
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constexpr size_t log2<uint64_t>(uint64_t v)
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{
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constexpr int MultiplyDeBruijnBitPosition[64] =
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{
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0, 58, 1, 59, 47, 53, 2, 60, 39, 48, 27, 54, 33, 42, 3, 61,
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51, 37, 40, 49, 18, 28, 20, 55, 30, 34, 11, 43, 14, 22, 4, 62,
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57, 46, 52, 38, 26, 32, 41, 50, 36, 17, 19, 29, 10, 13, 21, 56,
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45, 25, 31, 35, 16, 9, 12, 44, 24, 15, 8, 23, 7, 6, 5, 63
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};
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v |= v >> 1;
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v |= v >> 2;
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v |= v >> 4;
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v |= v >> 8;
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v |= v >> 16;
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v |= v >> 32;
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return MultiplyDeBruijnBitPosition[(uint64_t)(v * 0x03f6eaf2cd271461) >> 58];
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}
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static_assert(log2<uint32_t>(7) == 2, "bad log2");
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static_assert(log2<uint32_t>(8) == 3, "bad log2");
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template<typename word_t>
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constexpr size_t msb(word_t v);
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template<>
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constexpr size_t msb<uint32_t>(uint32_t v)
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{
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auto l = log2(v);
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return l + (((1 << l) ^ v) != 0);
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}
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template<>
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constexpr size_t msb<uint64_t>(uint64_t v)
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{
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auto l = log2(v);
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return l + (((1 << l) ^ v) != 0);
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}
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static_assert(msb<uint32_t>(7) == 3, "bad msb");
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static_assert(msb<uint32_t>(8) == 3, "bad msb");
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}
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}
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