lib/libm/src/s_ilogb.c

   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 1.12 2002/05/26 22:01:56 wiz 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 #include "math_private.h"
  26
  27 int
  28 ilogb(double x)
  29 {
  30         int32_t hx,lx,ix;
  31
  32         GET_HIGH_WORD(hx,x);
  33         hx &= 0x7fffffff;
  34         if(hx<0x00100000) {
  35             GET_LOW_WORD(lx,x);
  36             if((hx|lx)==0)
  37                 return 0x80000001;      /* ilogb(0) = 0x80000001 */
  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 return 0x7fffffff;
  48 }