BUG: special: Fix incorrect handling of nan input in gammainc and gammaincc (#22441)

* BUG: Add nan checks in gammainc and gammaincc scalar kernels

* TST: Add tests for nan inputs for gammainc(c)

* BUG: fix chdtrc out of domain case

* TST: Add nan arg tests for chdtr(c)

Author: steppi

include/xsf/cephes/chdtr.h

@@ -162,9 +162,10 @@ namespace xsf {
 namespace cephes {
 
     XSF_HOST_DEVICE inline double chdtrc(double df, double x) {
-
-        if (x < 0.0)
-            return 1.0; /* modified by T. Oliphant */
+        if (x < 0.0) {
+            set_error("chdtr", SF_ERROR_DOMAIN, NULL);
+            return (std::numeric_limits<double>::quiet_NaN());
+	}
         return (igamc(df / 2.0, x / 2.0));
     }
 

include/xsf/cephes/igam.h

@@ -328,6 +328,10 @@ namespace cephes {
     XSF_HOST_DEVICE inline double igam(double a, double x) {
         double absxma_a;
 
+	if (std::isnan(a) || std::isnan(x)) {
+	    return std::numeric_limits<double>::quiet_NaN();
+	}
+
         if (x < 0 || a < 0) {
             set_error("gammainc", SF_ERROR_DOMAIN, NULL);
             return std::numeric_limits<double>::quiet_NaN();
@@ -367,6 +371,10 @@ namespace cephes {
     XSF_HOST_DEVICE double igamc(double a, double x) {
         double absxma_a;
 
+	if (std::isnan(a) || std::isnan(x)) {
+	    return std::numeric_limits<double>::quiet_NaN();
+	}
+
         if (x < 0 || a < 0) {
             set_error("gammaincc", SF_ERROR_DOMAIN, NULL);
             return std::numeric_limits<double>::quiet_NaN();