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      1 
      2 /* @(#)s_ilogb.c 1.3 95/01/18 */
      3 /*
      4  * ====================================================
      5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
      6  *
      7  * Developed at SunSoft, a Sun Microsystems, Inc. business.
      8  * Permission to use, copy, modify, and distribute this
      9  * software is freely granted, provided that this notice
     10  * is preserved.
     11  * ====================================================
     12  */
     13 
     14 /* ieee_ilogb(double x)
     15  * return the binary exponent of non-zero x
     16  * ieee_ilogb(0) = 0x80000001
     17  * ieee_ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
     18  */
     19 
     20 #include "fdlibm.h"
     21 
     22 #ifdef __STDC__
     23 	int ieee_ilogb(double x)
     24 #else
     25 	int ieee_ilogb(x)
     26 	double x;
     27 #endif
     28 {
     29 	int hx,lx,ix;
     30 
     31 	hx  = (__HI(x))&0x7fffffff;	/* high word of x */
     32 	if(hx<0x00100000) {
     33 	    lx = __LO(x);
     34 	    if((hx|lx)==0)
     35 		return 0x80000001;	/* ieee_ilogb(0) = 0x80000001 */
     36 	    else			/* subnormal x */
     37 		if(hx==0) {
     38 		    for (ix = -1043; lx>0; lx<<=1) ix -=1;
     39 		} else {
     40 		    for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
     41 		}
     42 	    return ix;
     43 	}
     44 	else if (hx<0x7ff00000) return (hx>>20)-1023;
     45 	else return 0x7fffffff;
     46 }
     47