BUG: expi returns NaN upon calling sc.expi(inf) (#66)

ChrisAB · web-flow · commit 7c23abda327e · 2025-10-08T10:48:07.000-05:00
diff --git a/include/xsf/expint.h b/include/xsf/expint.h
@@ -149,6 +149,9 @@ XSF_HOST_DEVICE inline double expi(double x) {
             }
         }
         ei = ga + std::log(x) + x * ei;
+    } else if (std::isinf(x)) {
+        // Special use-case needed because exp(inf) / inf is undefined/NaN
+        return std::numeric_limits<double>::infinity();
     } else {
         // Asymptotic expansion (the series is not convergent)
         ei = 1.0;

Original file line number	Diff line number	Diff line change
`@@ -149,6 +149,9 @@ XSF_HOST_DEVICE inline double expi(double x) {`
`149`	`149`	`}`
`150`	`150`	`}`
`151`	`151`	`ei = ga + std::log(x) + x * ei;`
	`152`	`+ } else if (std::isinf(x)) {`
	`153`	`+ // Special use-case needed because exp(inf) / inf is undefined/NaN`
	`154`	`+ return std::numeric_limits<double>::infinity();`
`152`	`155`	`} else {`
`153`	`156`	`// Asymptotic expansion (the series is not convergent)`
`154`	`157`	`ei = 1.0;`