1 files changed, 45 insertions, 0 deletions
diff --git a/src/math/s_ilogb.c b/src/math/s_ilogb.c
new file mode 100644
index 00000000..f1ac498a
--- /dev/null
+++ b/src/math/s_ilogb.c
@@ -0,0 +1,45 @@
+/* @(#)s_ilogb.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.
+ * ====================================================
+ */
+
+/* ilogb(double x)
+ * return the binary exponent of non-zero x
+ * ilogb(0) = FP_ILOGB0
+ * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
+ * ilogb(inf) = INT_MAX (no signal is raised)
+ */
+
+#include <limits.h>
+
+#include <math.h>
+#include "math_private.h"
+
+int ilogb(double x)
+{
+        int32_t hx,lx,ix;
+
+        EXTRACT_WORDS(hx,lx,x);
+        hx &= 0x7fffffff;
+        if(hx<0x00100000) {
+            if((hx|lx)==0)
+                return FP_ILOGB0;
+            else                        /* subnormal x */
+                if(hx==0) {
+                    for (ix = -1043; lx>0; lx<<=1) ix -=1;
+                } else {
+                    for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
+                }
+            return ix;
+        }
+        else if (hx<0x7ff00000) return (hx>>20)-1023;
+        else if (hx>0x7ff00000 || lx!=0) return FP_ILOGBNAN;
+        else return INT_MAX;
+}