gh-132908: Add math.isnormal/issubnormal() functions

Doc/library/math.rst

@@ -53,6 +53,8 @@ noted otherwise, all return values are floats.
 :func:`frexp(x) <frexp>`                              Mantissa and exponent of *x*
 :func:`isclose(a, b, rel_tol, abs_tol) <isclose>`     Check if the values *a* and *b* are close to each other
 :func:`isfinite(x) <isfinite>`                        Check if *x* is neither an infinity nor a NaN
+:func:`isnormal(x) <isnormal>`                        Check if *x* is a normal floating-point number
+:func:`issubnormal(x) <issubnormal>`                  Check if *x* is a subnormal floating-point number
 :func:`isinf(x) <isinf>`                              Check if *x* is a positive or negative infinity
 :func:`isnan(x) <isnan>`                              Check if *x* is a NaN  (not a number)
 :func:`ldexp(x, i) <ldexp>`                           ``x * (2**i)``, inverse of function :func:`frexp`
@@ -373,6 +375,24 @@ Floating point manipulation functions
    .. versionadded:: 3.2
 
 
+.. function:: isnormal(x)
+
+   Return ``True`` if *x* is a normal floating-point number, that is a finite
+   nonzero number that is not a subnormal (see :func:`issubnormal`).
+   Return ``False`` otherwise.
+
+   .. versionadded:: next
+
+
+.. function:: issubnormal(x)
+
+   Return ``True`` if *x* is a subnormal floating-point number, that is a finite
+   nonzero number with a magnitude smaller than the smallest positive normal
+   number, see :data:`sys.float_info.min`.  Return ``False`` otherwise.
+
+   .. versionadded:: next
+
+
 .. function:: isinf(x)
 
    Return ``True`` if *x* is a positive or negative infinity, and

Doc/whatsnew/3.14.rst

@@ -1454,7 +1454,7 @@ math
 ----
 
 * Added more detailed error messages for domain errors in the module.
-  (Contributed by by Charlie Zhao and Sergey B Kirpichev in :gh:`101410`.)
+  (Contributed by Charlie Zhao and Sergey B Kirpichev in :gh:`101410`.)
 
 
 mimetypes

Doc/whatsnew/3.15.rst

@@ -105,6 +105,13 @@ difflib
   (Contributed by Jiahao Li in :gh:`134580`.)
 
 
+math
+----
+
+* Add :func:`math.isnormal` and :func:`math.issubnormal` functions.
+  (Contributed by Sergey B Kirpichev in :gh:`132908`.)
+
+
 shelve
 ------
 

Lib/test/test_math.py

@@ -1973,6 +1973,28 @@ def testIsfinite(self):
         self.assertFalse(math.isfinite(float("inf")))
         self.assertFalse(math.isfinite(float("-inf")))
 
+    def testIsnormal(self):
+        self.assertTrue(math.isnormal(1.25))
+        self.assertTrue(math.isnormal(-1.0))
+        self.assertFalse(math.isnormal(0.0))
+        self.assertFalse(math.isnormal(-0.0))
+        self.assertFalse(math.isnormal(INF))
+        self.assertFalse(math.isnormal(NINF))
+        self.assertFalse(math.isnormal(NAN))
+        self.assertFalse(math.isnormal(FLOAT_MIN/2))
+        self.assertFalse(math.isnormal(-FLOAT_MIN/2))
+
+    def testIssubnormal(self):
+        self.assertFalse(math.issubnormal(1.25))
+        self.assertFalse(math.issubnormal(-1.0))
+        self.assertFalse(math.issubnormal(0.0))
+        self.assertFalse(math.issubnormal(-0.0))
+        self.assertFalse(math.issubnormal(INF))
+        self.assertFalse(math.issubnormal(NINF))
+        self.assertFalse(math.issubnormal(NAN))
+        self.assertTrue(math.issubnormal(FLOAT_MIN/2))
+        self.assertTrue(math.issubnormal(-FLOAT_MIN/2))
+
     def testIsnan(self):
         self.assertTrue(math.isnan(float("nan")))
         self.assertTrue(math.isnan(float("-nan")))

Misc/NEWS.d/next/Library/2025-04-25-16-06-53.gh-issue-132908.wV5rja.rst

@@ -0,0 +1,2 @@
+Add :func:`math.isnormal` and :func:`math.issubnormal` functions.  Patch by
+Sergey B Kirpichev.

Modules/mathmodule.c

@@ -3118,6 +3118,44 @@ math_isfinite_impl(PyObject *module, double x)
 }
 
 
+/*[clinic input]
+math.isnormal
+
+    x: double
+    /
+
+Return True if x is normal, and False otherwise.
+[clinic start generated code]*/
+
+static PyObject *
+math_isnormal_impl(PyObject *module, double x)
+/*[clinic end generated code: output=c7b302b5b89c3541 input=fdaa00c58aa7bc17]*/
+{
+    return PyBool_FromLong((long)isnormal(x));
+}
+
+
+/*[clinic input]
+math.issubnormal
+
+    x: double
+    /
+
+Return True if x is subnormal, and False otherwise.
+[clinic start generated code]*/
+
+static PyObject *
+math_issubnormal_impl(PyObject *module, double x)
+/*[clinic end generated code: output=4e76ac98ddcae761 input=9a20aba7107d0d95]*/
+{
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L
+    return PyBool_FromLong((long)issubnormal(x));
+#else
+    return PyBool_FromLong((long)(isfinite(x) && x && !isnormal(x)));
+#endif
+}
+
+
 /*[clinic input]
 math.isnan
 
@@ -4145,6 +4183,8 @@ static PyMethodDef math_methods[] = {
     MATH_HYPOT_METHODDEF
     MATH_ISCLOSE_METHODDEF
     MATH_ISFINITE_METHODDEF
+    MATH_ISNORMAL_METHODDEF
+    MATH_ISSUBNORMAL_METHODDEF
     MATH_ISINF_METHODDEF
     MATH_ISNAN_METHODDEF
     MATH_ISQRT_METHODDEF