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bpo-29782: Consolidate _Py_Bit_Length() (GH-20739)

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In GH-2866, _Py_Bit_Length() was added to pymath.h for lack of a better
location. GH-20518 added a more appropriate header file for bit utilities. It
also shows how to properly use intrinsics. This allows reconsidering bpo-29782.

* Move the function to the new header.
* Changed return type to match __builtin_clzl() and reviewed usage.
* Use intrinsics where available.
* Pick a fallback implementation suitable for inlining.
This commit is contained in:
Niklas Fiekas 2020-06-15 14:33:48 +02:00 • committed by GitHub
parent 25f38d7044
commit 794e7d1ab2
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6 changed files with 100 additions and 36 deletions
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8
Include/pymath.h
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@ -227,12 +227,4 @@ PyAPI_FUNC(void) _Py_set_387controlword(unsigned short);
* behavior. */
#define _Py_InIntegralTypeRange(type, v) (_Py_IntegralTypeMin(type) <= v && v <= _Py_IntegralTypeMax(type))
/* Return the smallest integer k such that n < 2**k, or 0 if n == 0.
* Equivalent to floor(log2(x))+1. Also equivalent to: bitwidth_of_type -
* count_leading_zero_bits(x)
*/
#ifndef Py_LIMITED_API
PyAPI_FUNC(unsigned int) _Py_bit_length(unsigned long d);
#endif
#endif /* Py_PYMATH_H */