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+/* @(#)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;
+}