8000 add `math.signbit` · python/cpython@5e4db08 · GitHub
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add math.signbit 
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‎Doc/library/math.rst

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@@ -59,6 +59,7 @@ noted otherwise, all return values are floats.
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:func:`isnan(x) <isnan>` Check if *x* is a NaN (not a number)
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:func:`ldexp(x, i) <ldexp>` ``x * (2**i)``, inverse of function :func:`frexp`
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:func:`nextafter(x, y, steps) <nextafter>` Floating-point value *steps* steps after *x* towards *y*
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:func:`signbit(x) <signbit>` Check if *x* is a negative number
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:func:`ulp(x) <ulp>` Value of the least significant bit of *x*
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**Power, exponential and logarithmic functions**
@@ -431,6 +432,15 @@ Floating point manipulation functions
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Added the *steps* argument.
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.. function:: signbit(x)
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Return :const:`True` if *x* is negative and :const:`False` otherwise.
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This is useful to detect the sign bit of zeroes, infinities and NaNs.
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.. versionadded:: next
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.. function:: ulp(x)
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Return the value of the least significant bit of the float *x*:

‎Doc/whatsnew/3.15.rst

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@@ -115,6 +115,9 @@ math
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* Add :func:`math.isnormal` and :func:`math.issubnormal` functions.
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(Contributed by Sergey B Kirpichev in :gh:`132908`.)
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* Add :func:`math.signbit` function.
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(Contributed by Bénédikt Tran in :gh:`135853`.)
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os.path
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-------

‎Lib/test/test_math.py

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@@ -17,8 +17,13 @@
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eps = 1E-05
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NAN = float('nan')
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NNAN = float('-nan')
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DNAN = decimal.Decimal("nan")
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DNNAN = decimal.Decimal("-nan")
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INF = float('inf')
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NINF = float('-inf')
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DINF = decimal.Decimal("inf")
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DNINF = decimal.Decimal("-inf")
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FLOAT_MAX = sys.float_info.max
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FLOAT_MIN = sys.float_info.min
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@@ -475,6 +480,14 @@ def testCopysign(self):
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# similarly, copysign(2., NAN) could be 2. or -2.
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self.assertEqual(abs(math.copysign(2., NAN)), 2.)
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def test_signbit(self):
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for arg in [0, 0., 1, 1., INF, NAN, DINF, DNAN]:
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with self.subTest('positive', arg=arg):
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self.assertFalse(math.signbit(arg))
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for arg in [-0., -1, -1., NINF, NNAN, DNINF, DNNAN]:
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with self.subTest('negative', arg=arg):
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self.assertTrue(math.signbit(arg))
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def testCos(self):
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self.assertRaises(TypeError, math.cos)
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self.ftest('cos(-pi/2)', math.cos(-math.pi/2), 0, abs_tol=math.ulp(1))
@@ -1387,7 +1400,6 @@ def __rmul__(self, other):
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args = ((-5, -5, 10), (1.5, 4611686018427387904, 2305843009213693952))
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self.assertEqual(sumprod(*args), 0.0)
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@requires_IEEE_754
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@unittest.skipIf(HAVE_DOUBLE_ROUNDING,
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"sumprod() accuracy not guaranteed on machines with double rounding")
@@ -2486,7 +2498,6 @@ def test_nextafter(self):
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with self.assertRaises(ValueError):
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math.nextafter(1.0, INF, steps=-1)
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@requires_IEEE_754
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def test_ulp(self):
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self.assertEqual(math.ulp(1.0), sys.float_info.epsilon)

‎Misc/NEWS.d/next/Library/2025-06-24-10-23-37.gh-issue-135853.6xDNOG.rst

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@@ -0,0 +1,2 @@
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:mod:`math`: expose C99 :func:`~math.signbit` function to determine whether
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a floating-point value is negative. Patch by Bénédikt Tran.

‎Modules/clinic/mathmodule.c.h

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‎Modules/mathmodule.c

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@@ -1233,6 +1233,25 @@ FUNC2(remainder, m_remainder,
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"Return x - n*y where n*y is the closest integer multiple of y.\n"
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"In the case where x is exactly halfway between two multiples of\n"
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"y, the nearest even value of n is used. The result is always exact.")
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/*[clinic input]
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math.signbit
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x: double
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/
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Return True if 'x' is negative and False otherwise.
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This is useful to detect the sign bit of zeroes, infinities and NaNs.
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[clinic start generated code]*/
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static PyObject *
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math_signbit_impl(PyObject *module, double x)
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/*[clinic end generated code: output=20c5f20156a9b871 input=1765b06afd3c4bd0]*/
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{
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return PyBool_FromLong(signbit(x));
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}
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FUNC1D(sin, sin, 0,
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"sin($module, x, /)\n--\n\n"
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"Return the sine of x (measured in radians).",
@@ -4199,6 +4218,7 @@ static PyMethodDef math_methods[] = {
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MATH_POW_METHODDEF
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MATH_RADIANS_METHODDEF
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{"remainder", _PyCFunction_CAST(math_remainder), METH_FASTCALL, math_remainder_doc},
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MATH_SIGNBIT_METHODDEF
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{"sin", math_sin, METH_O, math_sin_doc},
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{"sinh", math_sinh, METH_O, math_sinh_doc},
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{"sqrt", math_sqrt, METH_O, math_sqrt_doc},

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