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gh-99761: Add _PyLong_IsPositiveSingleDigit function to check for single digit integers (#100064)

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Pieter Eendebak 2022-12-22 12:30:18 +01:00 • committed by GitHub
parent 68981578ec
commit 2b82c36f17
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3 changed files with 25 additions and 10 deletions
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19
Include/internal/pycore_long.h
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@ -110,6 +110,25 @@ PyAPI_FUNC(char*) _PyLong_FormatBytesWriter(
int base,
int alternate);
/* Return 1 if the argument is positive single digit int */
static inline int
_PyLong_IsPositiveSingleDigit(PyObject* sub) {
/* For a positive single digit int, the value of Py_SIZE(sub) is 0 or 1.
We perform a fast check using a single comparison by casting from int
to uint which casts negative numbers to large positive numbers.
For details see Section 14.2 "Bounds Checking" in the Agner Fog
optimization manual found at:
https://www.agner.org/optimize/optimizing_cpp.pdf
The function is not affected by -fwrapv, -fno-wrapv and -ftrapv
compiler options of GCC and clang
*/
assert(PyLong_CheckExact(sub));
Py_ssize_t signed_size = Py_SIZE(sub);
return ((size_t)signed_size) <= 1;
}
#ifdef __cplusplus
}
#endif