BUG: fix non-c99 fallback for np.inf input to log1p/expm1

closes gh-4225

1 files changed, 23 insertions, 13 deletions

diff --git a/numpy/core/src/npymath/npy_math.c.src b/numpy/core/src/npymath/npy_math.c.src
index 61f1d79ab..1ca7033af 100644
--- a/numpy/core/src/npymath/npy_math.c.src
+++ b/numpy/core/src/npymath/npy_math.c.src
@@ -65,14 +65,19 @@
 #ifndef HAVE_EXPM1
 double npy_expm1(double x)
 {
-    const double u = npy_exp(x);
-
-    if (u == 1.0) {
+    if (npy_isinf(x) && x > 0) {
         return x;
-    } else if (u - 1.0 == -1.0) {
-        return -1;
-    } else {
-        return (u - 1.0) * x/npy_log(u);
+    }
+    else {
+        const double u = npy_exp(x);
+
+        if (u == 1.0) {
+            return x;
+        } else if (u - 1.0 == -1.0) {
+            return -1;
+        } else {
+            return (u - 1.0) * x/npy_log(u);
+        }
     }
 }
 #endif
@@ -80,13 +85,18 @@ double npy_expm1(double x)
 #ifndef HAVE_LOG1P
 double npy_log1p(double x)
 {
-    const double u = 1. + x;
-    const double d = u - 1.;
-
-    if (d == 0) {
+    if (npy_isinf(x) && x > 0) {
         return x;
-    } else {
-        return npy_log(u) * x / d;
+    }
+    else {
+        const double u = 1. + x;
+        const double d = u - 1.;
+
+        if (d == 0) {
+            return x;
+        } else {
+            return npy_log(u) * x / d;
+        }
     }
 }
 #endif