bpo-36106: Resolve sinpi name clash with libm (IEEE-754 violation). (G…

…H-12027)

The standard math library (libm) may follow IEEE-754 recommendation to
include an implementation of sinPi(), i.e. sinPi(x):=sin(pi*x).
And this triggers a name clash, found by FreeBSD developer
Steve Kargl, who worken on putting sinpi into libm used on FreeBSD
(it has to be named "sinpi", not "sinPi", cf. e.g.
https://en.cppreference.com/w/c/experimental/fpext4).
(cherry picked from commit f57cd82)

Co-authored-by: Dima Pasechnik <dimpase@gmail.com>

Misc/NEWS.d/next/Library/2019-02-25-13-21-43.bpo-36106.VuhEiQ.rst

@@ -0,0 +1 @@
+Resolve potential name clash with libm's sinpi(). Patch by Dmitrii Pasechnik.

Modules/mathmodule.c

@@ -77,7 +77,7 @@ static const double sqrtpi = 1.772453850905516027298167483341145182798;
 #endif /* !defined(HAVE_ERF) || !defined(HAVE_ERFC) */
 
 static double
-sinpi(double x)
+m_sinpi(double x)
 {
     double y, r;
     int n;
@@ -305,7 +305,7 @@ m_tgamma(double x)
        integer. */
     if (absx > 200.0) {
         if (x < 0.0) {
-            return 0.0/sinpi(x);
+            return 0.0/m_sinpi(x);
         }
         else {
             errno = ERANGE;
@@ -329,7 +329,7 @@ m_tgamma(double x)
     }
     z = z * lanczos_g / y;
     if (x < 0.0) {
-        r = -pi / sinpi(absx) / absx * exp(y) / lanczos_sum(absx);
+        r = -pi / m_sinpi(absx) / absx * exp(y) / lanczos_sum(absx);
         r -= z * r;
         if (absx < 140.0) {
             r /= pow(y, absx - 0.5);
@@ -400,7 +400,7 @@ m_lgamma(double x)
     r += (absx - 0.5) * (log(absx + lanczos_g - 0.5) - 1);
     if (x < 0.0)
         /* Use reflection formula to get value for negative x. */
-        r = logpi - log(fabs(sinpi(absx))) - log(absx) - r;
+        r = logpi - log(fabs(m_sinpi(absx))) - log(absx) - r;
     if (Py_IS_INFINITY(r))
         errno = ERANGE;
     return r;