POSIX: emulation for logb()

diff --git a/ext/POSIX/POSIX.xs b/ext/POSIX/POSIX.xs
index 7652416..5a2c306 100644 (file)
--- a/ext/POSIX/POSIX.xs
+++ b/ext/POSIX/POSIX.xs
@@ -2322,6 +2322,8 @@ acos(x)
        case 20:
 #ifdef c99_logb
            RETVAL = c99_logb(x);
+#elif defined(c99_log2) && FLT_RADIX == 2
+           RETVAL = Perl_floor(c99_log2(PERL_ABS(x)));
 #else
            not_here("logb");
 #endif