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#include "internal/pystate.h" |
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#include "internal/hamt.h" |
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-/* popcnt support in Visual Studio */ |
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-#ifdef _MSC_VER |
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-#include <intrin.h> |
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-#endif |
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- |
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/* |
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This file provides an implemention of an immutable mapping using the |
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Hash Array Mapped Trie (or HAMT) datastructure. |
| @@ -440,18 +435,21 @@ hamt_bitpos(int32_t hash, uint32_t shift) |
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static inline uint32_t |
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hamt_bitcount(uint32_t i) |
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{ |
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-#if defined(__GNUC__) && (__GNUC__ > 4) |
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-return (uint32_t)__builtin_popcountl(i); |
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-#elif defined(__clang__) && (__clang_major__ > 3) |
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-return (uint32_t)__builtin_popcountl(i); |
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-#elif defined(_MSC_VER) |
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-return (uint32_t)__popcnt(i); |
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-#else |
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-/* https://graphics.stanford.edu/\~seander/bithacks.html */ |
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+/* We could use native popcount instruction but that would |
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+ require to either add configure flags to enable SSE4.2 |
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+ support or to detect it dynamically. Otherwise, we have |
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+ a risk of CPython not working properly on older hardware. |
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+ |
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+ In practice, there's no observable difference in |
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+ performance between using a popcount instruction or the |
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+ following fallback code. |
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+ |
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+ The algorithm is copied from: |
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+ https://graphics.stanford.edu/\~seander/bithacks.html |
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+ */ |
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i = i - ((i >> 1) & 0x55555555); |
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i = (i & 0x33333333) + ((i >> 2) & 0x33333333); |
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return ((i + (i >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; |
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-#endif |
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} |
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static inline uint32_t |