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[Basic] Manually implement popcount when not available #73384

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merged 1 commit into from
May 2, 2024
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[Basic] Manually implement popcount when not available #73384

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14 changes: 11 additions & 3 deletions include/swift/Basic/MathUtils.h
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,9 @@
#ifndef SWIFT_BASIC_MATH_UTILS_H
#define SWIFT_BASIC_MATH_UTILS_H

#include "Compiler.h"
#include <cstddef>
#include <cstdint>

#if SWIFT_COMPILER_IS_MSVC
#include <intrin.h>
Expand All @@ -38,11 +40,17 @@ static inline size_t roundUpToAlignMask(size_t size, size_t alignMask) {
}

static inline unsigned popcount(unsigned value) {
#if SWIFT_COMPILER_IS_MSVC
#if SWIFT_COMPILER_IS_MSVC && (defined(_M_IX86) || defined(_M_X64))
// The __popcnt intrinsic is only available when targetting x86{_64} with MSVC.
return __popcnt(value);
#else
// Assume we have a compiler with this intrinsic.
#elif __has_builtin(__builtin_popcount)
return __builtin_popcount(value);
#else
// From llvm/ADT/bit.h which the runtime doesn't have access to (yet?)
uint32_t v = value;
v = v - ((v >> 1) & 0x55555555);
v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
return int(((v + (v >> 4) & 0xF0F0F0F) * 0x1010101) >> 24);
#endif
}

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