1 files changed, 34 insertions, 0 deletions
diff --git a/src/math/s_logb.c b/src/math/s_logb.c
new file mode 100644
index 00000000..be399c77
--- /dev/null
+++ b/src/math/s_logb.c
@@ -0,0 +1,34 @@
+/* @(#)s_logb.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+/*
+ * double logb(x)
+ * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
+ * Use ilogb instead.
+ */
+
+#include <math.h>
+#include "math_private.h"
+
+double
+logb(double x)
+{
+        int32_t lx,ix;
+        EXTRACT_WORDS(ix,lx,x);
+        ix &= 0x7fffffff;                       /* high |x| */
+        if((ix|lx)==0) return -1.0/fabs(x);
+        if(ix>=0x7ff00000) return x*x;
+        if((ix>>=20)==0)                        /* IEEE 754 logb */
+                return -1022.0;
+        else
+                return (double) (ix-1023);
+}