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bpo-39310: Add math.ulp(x) (GH-17965)

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Add math.ulp(): return the value of the least significant bit
of a float.
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Victor Stinner 2020-01-13 12:44:35 +01:00 • committed by GitHub
parent 7ba6f18de2
commit 0b2ab21956
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GPG key ID: 4AEE18F83AFDEB23
7 changed files with 144 additions and 37 deletions
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32
Modules/mathmodule.c
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@ -3314,6 +3314,37 @@ math_nextafter_impl(PyObject *module, double x, double y)
}
/*[clinic input]
math.ulp -> double
x: double
/
Return the value of the least significant bit of the float x.
[clinic start generated code]*/
static double
math_ulp_impl(PyObject *module, double x)
/*[clinic end generated code: output=f5207867a9384dd4 input=31f9bfbbe373fcaa]*/
{
if (Py_IS_NAN(x)) {
return x;
}
x = fabs(x);
if (Py_IS_INFINITY(x)) {
return x;
}
double inf = m_inf();
double x2 = nextafter(x, inf);
if (Py_IS_INFINITY(x2)) {
/* special case: x is the largest positive representable float */
x2 = nextafter(x, -inf);
return x - x2;
}
return x2 - x;
}
static PyMethodDef math_methods[] = {
{"acos", math_acos, METH_O, math_acos_doc},
{"acosh", math_acosh, METH_O, math_acosh_doc},
@ -3366,6 +3397,7 @@ static PyMethodDef math_methods[] = {
MATH_PERM_METHODDEF
MATH_COMB_METHODDEF
MATH_NEXTAFTER_METHODDEF
MATH_ULP_METHODDEF
{NULL, NULL} /* sentinel */
};