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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 #include <sys/cdefs.h>
     14 #if defined(LIBM_SCCS) && !defined(lint)
     15 __RCSID("$NetBSD: s_ilogb.c,v 1.16 2016/08/26 08:20:31 christos Exp $");
     16 #endif
     17 
     18 /* ilogb(double x)
     19  * return the binary exponent of non-zero x
     20  * ilogb(0) = 0x80000001
     21  * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
     22  */
     23 
     24 #include <math.h>
     25 #define __TEST_FENV
     26 #include <fenv.h>
     27 #ifndef __HAVE_FENV
     28 #define feraiseexcept(a)
     29 #endif
     30 #include "math_private.h"
     31 
     32 #ifndef __HAVE_LONG_DOUBLE
     33 __strong_alias(ilogbl,ilogb)
     34 #endif
     35 
     36 int
     37 ilogb(double x)
     38 {
     39 	int32_t hx, lx, ix;
     40 
     41 	GET_HIGH_WORD(hx, x);
     42 	hx &= 0x7fffffff;
     43 	if (hx < 0x00100000) {
     44 		GET_LOW_WORD(lx, x);
     45 		if ((hx | lx) == 0) {
     46 			feraiseexcept(FE_INVALID);
     47 			return FP_ILOGB0;	/* ilogb(0) = 0x80000001 */
     48 		}
     49 		if (hx == 0) {
     50 			for (ix = -1043; lx > 0; lx <<= 1) ix -= 1;
     51 		} else {
     52 			for (ix = -1022, hx <<= 11; hx > 0; hx <<= 1) ix -= 1;
     53 		}
     54 		return ix;
     55 	}
     56 
     57 	if (hx < 0x7ff00000) {
     58 		return (hx >> 20) - 1023;
     59 	}
     60 
     61 	feraiseexcept(FE_INVALID);
     62 	return isnan(x) ? FP_ILOGBNAN : INT_MAX;
     63 }
     64