No puede seleccionar más de 25 temas
Los temas deben comenzar con una letra o número, pueden incluir guiones ('-') y pueden tener hasta 35 caracteres de largo.
77 líneas
1.7 KiB
77 líneas
1.7 KiB
#pragma once
|
|
|
|
#include <stdint.h>
|
|
#include <stddef.h>
|
|
|
|
namespace gp {
|
|
namespace math {
|
|
|
|
template<typename word_t>
|
|
size_t log2(word_t v);
|
|
|
|
/**
|
|
Sean Eron Anderson
|
|
seander@cs.stanford.edu
|
|
**/
|
|
template<>
|
|
constexpr size_t log2<uint32_t>(uint32_t v)
|
|
{
|
|
constexpr int MultiplyDeBruijnBitPosition[32] =
|
|
{
|
|
0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
|
|
8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
|
|
};
|
|
|
|
v |= v >> 1;
|
|
v |= v >> 2;
|
|
v |= v >> 4;
|
|
v |= v >> 8;
|
|
v |= v >> 16;
|
|
|
|
return MultiplyDeBruijnBitPosition[(uint32_t)(v * 0x07C4ACDDU) >> 27];
|
|
}
|
|
|
|
template<>
|
|
constexpr size_t log2<uint64_t>(uint64_t v)
|
|
{
|
|
constexpr int MultiplyDeBruijnBitPosition[64] =
|
|
{
|
|
0, 58, 1, 59, 47, 53, 2, 60, 39, 48, 27, 54, 33, 42, 3, 61,
|
|
51, 37, 40, 49, 18, 28, 20, 55, 30, 34, 11, 43, 14, 22, 4, 62,
|
|
57, 46, 52, 38, 26, 32, 41, 50, 36, 17, 19, 29, 10, 13, 21, 56,
|
|
45, 25, 31, 35, 16, 9, 12, 44, 24, 15, 8, 23, 7, 6, 5, 63
|
|
};
|
|
|
|
v |= v >> 1;
|
|
v |= v >> 2;
|
|
v |= v >> 4;
|
|
v |= v >> 8;
|
|
v |= v >> 16;
|
|
v |= v >> 32;
|
|
|
|
return MultiplyDeBruijnBitPosition[(uint64_t)(v * 0x03f6eaf2cd271461ULL) >> 58];
|
|
}
|
|
|
|
static_assert(log2<uint32_t>(7) == 2, "bad log2");
|
|
static_assert(log2<uint32_t>(8) == 3, "bad log2");
|
|
|
|
template<typename word_t>
|
|
constexpr size_t msb(word_t v);
|
|
|
|
template<>
|
|
constexpr size_t msb<uint32_t>(uint32_t v)
|
|
{
|
|
auto l = log2(v);
|
|
return l + (((1 << l) ^ v) != 0);
|
|
}
|
|
template<>
|
|
constexpr size_t msb<uint64_t>(uint64_t v)
|
|
{
|
|
auto l = log2(v);
|
|
return l + (((1 << l) ^ v) != 0);
|
|
}
|
|
|
|
static_assert(msb<uint32_t>(7) == 3, "bad msb");
|
|
static_assert(msb<uint32_t>(8) == 3, "bad msb");
|
|
}
|
|
}
|