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Add a non-intrinsic version of findFirstSet to the EightBit library.

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Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
This commit is contained in:
Adrian Conlon 2019-07-21 11:25:06 +01:00
parent def1c58e9d
commit 9d34d7ec3d
1 changed files with 12 additions and 5 deletions
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17
inc/EightBitCompilerDefinitions.h
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@ -1,5 +1,8 @@
#pragma once #pragma once
#include <cassert>
#include <bitset>
#ifdef _MSC_VER #ifdef _MSC_VER
# include <intrin.h> # include <intrin.h>
#endif #endif
@ -9,9 +12,9 @@
#endif #endif
namespace EightBit { namespace EightBit {
[[nodiscard]] int countBits(uint8_t value) noexcept ; [[nodiscard]] int countBits(uint8_t value) noexcept;
[[nodiscard]] bool oddParity(uint8_t value) noexcept ; [[nodiscard]] bool oddParity(uint8_t value) noexcept;
[[nodiscard]] int findFirstSet(int value) noexcept ; [[nodiscard]] int findFirstSet(unsigned long value) noexcept;
constexpr void assume(int expression); constexpr void assume(int expression);
} }
@ -39,7 +42,7 @@ inline bool EightBit::oddParity(const uint8_t value) noexcept {
return countBits(value) % 2; return countBits(value) % 2;
} }
inline int EightBit::findFirstSet(const int value) noexcept { inline int EightBit::findFirstSet(const unsigned long value) noexcept {
#ifdef _MSC_VER #ifdef _MSC_VER
unsigned long index; unsigned long index;
if (_BitScanForward(&index, value)) if (_BitScanForward(&index, value))
@ -48,7 +51,11 @@ inline int EightBit::findFirstSet(const int value) noexcept {
#elif defined(__GNUG__) #elif defined(__GNUG__)
return __builtin_ffs(value); return __builtin_ffs(value);
#else #else
# error Find first set not implemented std::bitset<sizeof(unsigned long) * 8> bits(value);
for (size_t i = bits.size() - 1; i >= 0; --i)
if (bits.test(i))
return i + 1;
return 0;
#endif #endif
} }