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       ---
       s_ilogb.c (1240B)
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            1 /* @(#)s_ilogb.c 5.1 93/09/24 */
            2 /*
            3  * ====================================================
            4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
            5  *
            6  * Developed at SunPro, a Sun Microsystems, Inc. business.
            7  * Permission to use, copy, modify, and distribute this
            8  * software is freely granted, provided that this notice
            9  * is preserved.
           10  * ====================================================
           11  */
           12 
           13 #ifndef lint
           14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_ilogb.c,v 1.9 2004/10/09 17:14:28 stefanf Exp $";
           15 #endif
           16 
           17 /* ilogb(double x)
           18  * return the binary exponent of non-zero x
           19  * ilogb(0) = FP_ILOGB0
           20  * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
           21  * ilogb(inf) = INT_MAX (no signal is raised)
           22  */
           23 
           24 #include <limits.h>
           25 
           26 #include "math.h"
           27 #include "math_private.h"
           28 
           29         int ilogb(double x)
           30 {
           31         int32_t hx,lx,ix;
           32 
           33         EXTRACT_WORDS(hx,lx,x);
           34         hx &= 0x7fffffff;
           35         if(hx<0x00100000) {
           36             if((hx|lx)==0)
           37                 return FP_ILOGB0;
           38             else                        /* subnormal x */
           39                 if(hx==0) {
           40                     for (ix = -1043; lx>0; lx<<=1) ix -=1;
           41                 } else {
           42                     for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
           43                 }
           44             return ix;
           45         }
           46         else if (hx<0x7ff00000) return (hx>>20)-1023;
           47         else if (hx>0x7ff00000 || lx!=0) return FP_ILOGBNAN;
           48         else return INT_MAX;
           49 }