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-rw-r--r--math/math.h7
1 files changed, 7 insertions, 0 deletions
diff --git a/math/math.h b/math/math.h
index 5381f29e9a..d7487dda4a 100644
--- a/math/math.h
+++ b/math/math.h
@@ -196,6 +196,13 @@ enum
       : sizeof (x) == sizeof (double) ?					      \
         __isnan (x) : __isnanl (x))
 
+/* Return nonzero value is X is positive or negative infinity.  */
+# define isinf(x) \
+     (sizeof (x) == sizeof (float) ?					      \
+        __isinff (x)							      \
+      : sizeof (x) == sizeof (double) ?					      \
+        __isinf (x) : __isinfl (x))
+
 #endif /* Use ISO C 9X.  */
 
 #ifdef	__USE_MISC