gh-156695: Improve accuracy of complex div and pow

Author: hpkfft

Include/internal/pycore_complexobject.h

@@ -27,6 +27,29 @@ PyAPI_FUNC(Py_complex) _Py_cr_prod(Py_complex, double);
 PyAPI_FUNC(Py_complex) _Py_cr_quot(Py_complex, double);
 PyAPI_FUNC(Py_complex) _Py_rc_quot(double, Py_complex);
 
+static inline bool
+_Py_c_isnan(Py_complex a)
+{
+    return isnan(a.real) || isnan(a.imag);
+}
+
+static inline bool
+_Py_c_isinf(Py_complex a)
+{
+    return isinf(a.real) || isinf(a.imag);
+}
+
+static inline bool
+_Py_c_isfinite(Py_complex a)
+{
+    return isfinite(a.real) && isfinite(a.imag);
+}
+
+static inline bool
+_Py_c_iszero(Py_complex a)
+{
+    return a.real == 0.0 && a.imag == 0.0;
+}
 
 #ifdef __cplusplus
 }

Include/internal/pycore_pymath.h

@@ -10,10 +10,9 @@ extern "C" {
 
 
 /* _Py_ADJUST_ERANGE1(x)
- * _Py_ADJUST_ERANGE2(x, y)
- * Set errno to 0 before calling a libm function, and invoke one of these
- * macros after, passing the function result(s) (_Py_ADJUST_ERANGE2 is useful
- * for functions returning complex results).  This makes two kinds of
+ * Set errno to 0 before calling a libm function, and invoke this
+ * macro after, passing the function result(s).
+ * This makes two kinds of
  * adjustments to errno:  (A) If it looks like the platform libm set
  * errno=ERANGE due to underflow, clear errno. (B) If it looks like the
  * platform libm overflowed but didn't set errno, force errno to ERANGE.  In
@@ -42,20 +41,6 @@ static inline void _Py_ADJUST_ERANGE1(double x)
     }
 }
 
-static inline void _Py_ADJUST_ERANGE2(double x, double y)
-{
-    if (x == INFINITY || x == -INFINITY ||
-        y == INFINITY || y == -INFINITY)
-    {
-        if (errno == 0) {
-            errno = ERANGE;
-        }
-    }
-    else if (errno == ERANGE) {
-        errno = 0;
-    }
-}
-
 
 //--- HAVE_PY_SET_53BIT_PRECISION macro ------------------------------------
 //

Misc/NEWS.d/next/Core_and_Builtins/2026-09-03-11-36-44.gh-issue-156695.0ST8Qu.rst

@@ -0,0 +1,3 @@
+Improve accuracy of complex division and complex powers with small negative
+integer exponents.  This also applies to :c:func:`_Py_c_quot` and
+:c:func:`_Py_c_pow`.  Contributed by High Performance Kernels LLC.