gh-104263: Rely on Py_NAN and introduce Py_INFINITY (GH-104202)

This PR removes `_Py_dg_stdnan` and `_Py_dg_infinity` in favour of
using the standard `NAN` and `INFINITY` macros provided by C99.
This change has the side-effect of fixing a bug on MIPS where the
hard-coded value used by `_Py_dg_stdnan` gave a signalling NaN
rather than a quiet NaN.
---------

Co-authored-by: Mark Dickinson <dickinsm@gmail.com>

2 files changed, 10 insertions, 90 deletions

diff --git a/Modules/cmathmodule.c b/Modules/cmathmodule.c
index 914a697f8e..1a31bdc824 100644
--- a/Modules/cmathmodule.c
+++ b/Modules/cmathmodule.c
@@ -8,7 +8,6 @@
 
 #include "Python.h"
 #include "pycore_pymath.h"        // _PY_SHORT_FLOAT_REPR
-#include "pycore_dtoa.h"          // _Py_dg_stdnan()
 /* we need DBL_MAX, DBL_MIN, DBL_EPSILON, DBL_MANT_DIG and FLT_RADIX from
    float.h.  We assume that FLT_RADIX is either 2 or 16. */
 #include <float.h>
@@ -88,53 +87,6 @@ else {
 #endif
 #define CM_SCALE_DOWN (-(CM_SCALE_UP+1)/2)
 
-/* Constants cmath.inf, cmath.infj, cmath.nan, cmath.nanj.
-   cmath.nan and cmath.nanj are defined only when either
-   _PY_SHORT_FLOAT_REPR is 1 (which should be
-   the most common situation on machines using an IEEE 754
-   representation), or Py_NAN is defined. */
-
-static double
-m_inf(void)
-{
-#if _PY_SHORT_FLOAT_REPR == 1
-    return _Py_dg_infinity(0);
-#else
-    return Py_HUGE_VAL;
-#endif
-}
-
-static Py_complex
-c_infj(void)
-{
-    Py_complex r;
-    r.real = 0.0;
-    r.imag = m_inf();
-    return r;
-}
-
-#if _PY_SHORT_FLOAT_REPR == 1
-
-static double
-m_nan(void)
-{
-#if _PY_SHORT_FLOAT_REPR == 1
-    return _Py_dg_stdnan(0);
-#else
-    return Py_NAN;
-#endif
-}
-
-static Py_complex
-c_nanj(void)
-{
-    Py_complex r;
-    r.real = 0.0;
-    r.imag = m_nan();
-    return r;
-}
-
-#endif
 
 /* forward declarations */
 static Py_complex cmath_asinh_impl(PyObject *, Py_complex);
@@ -1274,23 +1226,22 @@ cmath_exec(PyObject *mod)
     if (PyModule_AddObject(mod, "tau", PyFloat_FromDouble(Py_MATH_TAU)) < 0) {
         return -1;
     }
-    if (PyModule_AddObject(mod, "inf", PyFloat_FromDouble(m_inf())) < 0) {
+    if (PyModule_AddObject(mod, "inf", PyFloat_FromDouble(Py_INFINITY)) < 0) {
         return -1;
     }
 
+    Py_complex infj = {0.0, Py_INFINITY};
     if (PyModule_AddObject(mod, "infj",
-                           PyComplex_FromCComplex(c_infj())) < 0) {
+                           PyComplex_FromCComplex(infj)) < 0) {
         return -1;
     }
-#if _PY_SHORT_FLOAT_REPR == 1
-    if (PyModule_AddObject(mod, "nan", PyFloat_FromDouble(m_nan())) < 0) {
+    if (PyModule_AddObject(mod, "nan", PyFloat_FromDouble(fabs(Py_NAN))) < 0) {
         return -1;
     }
-    if (PyModule_AddObject(mod, "nanj",
-                           PyComplex_FromCComplex(c_nanj())) < 0) {
+    Py_complex nanj = {0.0, fabs(Py_NAN)};
+    if (PyModule_AddObject(mod, "nanj", PyComplex_FromCComplex(nanj)) < 0) {
         return -1;
     }
-#endif
 
     /* initialize special value tables */
 
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index 3737a96545..f369b2c45c 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -59,7 +59,6 @@ raised for division by zero and mod by zero.
 #include "Python.h"
 #include "pycore_bitutils.h"      // _Py_bit_length()
 #include "pycore_call.h"          // _PyObject_CallNoArgs()
-#include "pycore_dtoa.h"          // _Py_dg_infinity()
 #include "pycore_long.h"          // _PyLong_GetZero()
 #include "pycore_moduleobject.h"  // _PyModule_GetState()
 #include "pycore_object.h"        // _PyObject_LookupSpecial()
@@ -389,34 +388,6 @@ lanczos_sum(double x)
     return num/den;
 }
 
-/* Constant for +infinity, generated in the same way as float('inf'). */
-
-static double
-m_inf(void)
-{
-#if _PY_SHORT_FLOAT_REPR == 1
-    return _Py_dg_infinity(0);
-#else
-    return Py_HUGE_VAL;
-#endif
-}
-
-/* Constant nan value, generated in the same way as float('nan'). */
-/* We don't currently assume that Py_NAN is defined everywhere. */
-
-#if _PY_SHORT_FLOAT_REPR == 1
-
-static double
-m_nan(void)
-{
-#if _PY_SHORT_FLOAT_REPR == 1
-    return _Py_dg_stdnan(0);
-#else
-    return Py_NAN;
-#endif
-}
-
-#endif
 
 static double
 m_tgamma(double x)
@@ -435,7 +406,7 @@ m_tgamma(double x)
     if (x == 0.0) {
         errno = EDOM;
         /* tgamma(+-0.0) = +-inf, divide-by-zero */
-        return copysign(Py_HUGE_VAL, x);
+        return copysign(Py_INFINITY, x);
     }
 
     /* integer arguments */
@@ -3938,7 +3909,7 @@ math_ulp_impl(PyObject *module, double x)
     if (Py_IS_INFINITY(x)) {
         return x;
     }
-    double inf = m_inf();
+    double inf = Py_INFINITY;
     double x2 = nextafter(x, inf);
     if (Py_IS_INFINITY(x2)) {
         /* special case: x is the largest positive representable float */
@@ -3975,14 +3946,12 @@ math_exec(PyObject *module)
     if (PyModule_AddObject(module, "tau", PyFloat_FromDouble(Py_MATH_TAU)) < 0) {
         return -1;
     }
-    if (PyModule_AddObject(module, "inf", PyFloat_FromDouble(m_inf())) < 0) {
+    if (PyModule_AddObject(module, "inf", PyFloat_FromDouble(Py_INFINITY)) < 0) {
         return -1;
     }
-#if _PY_SHORT_FLOAT_REPR == 1
-    if (PyModule_AddObject(module, "nan", PyFloat_FromDouble(m_nan())) < 0) {
+    if (PyModule_AddObject(module, "nan", PyFloat_FromDouble(fabs(Py_NAN))) < 0) {
         return -1;
     }
-#endif
     return 0;
 }