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bpo-29782: Consolidate _Py_Bit_Length() #20739

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Merged
vstinner merged 21 commits into from
Jun 15, 2020
Merged

bpo-29782: Consolidate _Py_Bit_Length() #20739

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281009c
bpo-29782: Consolidate _Py_Bit_Length()
niklasf Jun 8, 2020
65abb83
Specify required gcc version for __builtin_clzl
niklasf Jun 8, 2020
ce45ff2
Fix _BitScanReverse usage
niklasf Jun 8, 2020
6464ca6
Document reason for include
niklasf Jun 8, 2020
0bd4265
Ensure future compatibility
niklasf Jun 8, 2020
fbaca66
Do not try to support GCC < 3.4
niklasf Jun 8, 2020
436f68b
Coding style
niklasf Jun 8, 2020
ac664bc
Fix comment indent
niklasf Jun 8, 2020
3279d17
Do not factor out x != 0
niklasf Jun 8, 2020
525da3d
Fix and move _Py_bit_length_digit()
niklasf Jun 8, 2020
e487622
Add unit test for _Py_bit_length()
niklasf Jun 8, 2020
a338761
Remove useless cast in test
niklasf Jun 8, 2020
5a146f7
Use original implementation as fallback
niklasf Jun 8, 2020
8e3ce66
Re-enable intrinsics
niklasf Jun 8, 2020
86241f6
Explicitly cast sizeof
niklasf Jun 8, 2020
c7ccbe2
Better tests
niklasf Jun 8, 2020
dfceaf2
Explain Py_BUILD_ASSERT(sizeof(unsigned long) <= 4)
niklasf Jun 8, 2020
fbf01ae
Use volatile so test actually runs intrinsic
niklasf Jun 8, 2020
991622b
Remove trailing spaces
niklasf Jun 8, 2020
462d995
_Py_bit_length_digit -> bit_length_digit
niklasf Jun 8, 2020
98fc7a8
Fixup test expectations
niklasf Jun 8, 2020
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Do not try to support GCC < 3.4
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@niklasf
niklasf committed Jun 8, 2020
commit fbaca66885fdfb64edcbe5ec45ec590405e98e79
3 changes: 2 additions & 1 deletion Include/internal/pycore_bitutils.h
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Expand Up @@ -138,7 +138,8 @@ _Py_bit_length(unsigned long x) {
if (x == 0) {
return 0;
}
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#if (defined(__clang__) || (defined(__GNUC__) && (((__GNUC__ == 3) && (__GNUC_MINOR__ >= 4)) || (__GNUC__ >= 4))))
#if (defined(__clang__) || defined(__GNUC__))
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// __builtin_clzl() is available since GCC 3.4.
// Undefined behavior for x == 0.
return sizeof(unsigned long) * 8 - __builtin_clzl(x);
#elif defined(_MSC_VER)
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