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Use bitmath builtins for FindLastBit

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This commit is contained in:
Jonathan G Rennison
2023-08-18 13:38:39 +01:00
parent c49651ae7b
commit 87911bdf47
3 changed files with 28 additions and 3 deletions
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2
src/core/bitmath_func.cpp
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@@ -62,7 +62,7 @@ uint8 FindFirstBit64(uint64 x)
* @param x The value to search
* @return The position of the last bit set
*/
uint8 FindLastBit(uint64 x)
uint8 FindLastBit64(uint64 x)
{
if (x == 0) return 0;

27
src/core/bitmath_func.hpp
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@@ -240,7 +240,32 @@ static inline uint8 FindFirstBit(T value)
#endif
}
uint8 FindLastBit(uint64 x);
/**
* Search the last set bit in an integer variable.
*
* @param value The value to search
* @return The position of the last bit set, or 0 when value is 0
*/
template <typename T>
static inline uint8 FindLastBit(T value)
{
static_assert(sizeof(T) <= sizeof(unsigned long long));
#ifdef WITH_BITMATH_BUILTINS
if (value == 0) return 0;
typename std::make_unsigned<T>::type unsigned_value = value;
if (sizeof(T) <= sizeof(unsigned int)) {
return __builtin_clz(1) - __builtin_clz(unsigned_value);
} else if (sizeof(T) == sizeof(unsigned long)) {
return __builtin_clzl(1) - __builtin_clzl(unsigned_value);
} else {
return __builtin_clzll(1) - __builtin_ctzll(unsigned_value);
}
#else
extern uint8 FindLastBit64(uint64 x);
return FindLastBit64(value);
#endif
}
/**
* Finds the position of the first non-zero bit in an integer.