math: fix logb*.c exceptions now that ilogb raises invalid

[musl] / src / math / logb.c

diff --git a/src/math/logb.c b/src/math/logb.c
index f7cd761..624425a 100644 (file)
--- a/src/math/logb.c
+++ b/src/math/logb.c
@@ -1,20 +1,17 @@
-#include <limits.h>
 #include "libm.h"
 
 /*
 special cases:
-       logb(+-0) = -inf
+       logb(+-0) = -inf, and raise divbyzero
        logb(+-inf) = +inf
        logb(nan) = nan
-these are calculated at runtime to raise fp exceptions
 */
 
-double logb(double x) {
-       int i = ilogb(x);
-
-       if (i == FP_ILOGB0)
-               return -1.0/fabs(x);
-       if (i == FP_ILOGBNAN || i == INT_MAX)
+double logb(double x)
+{
+       if (!isfinite(x))
                return x * x;
-       return i;
+       if (x == 0)
+               return -1/(x+0);
+       return ilogb(x);
 }