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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 }
     50