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 /* ilogb(double x)
  14  * return the binary exponent of non-zero x
  15  * ilogb(0) = 0x80000001
  16  * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
  17  */
  18
  19 #include <float.h>
  20 #include <math.h>
  21
  22 #include "math_private.h"
  23
  24 int
  25 ilogb(double x)
  26 {
  27         int32_t hx,lx,ix;
  28
  29         GET_HIGH_WORD(hx,x);
  30         hx &= 0x7fffffff;
  31         if(hx<0x00100000) {
  32             GET_LOW_WORD(lx,x);
  33             if((hx|lx)==0)
  34                 return 0x80000001;      /* ilogb(0) = 0x80000001 */
  35             else                        /* subnormal x */
  36                 if(hx==0) {
  37                     for (ix = -1043; lx>0; lx<<=1) ix -=1;
  38                 } else {
  39                     for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
  40                 }
  41             return ix;
  42         }
  43         else if (hx<0x7ff00000) return (hx>>20)-1023;
  44         else return 0x7fffffff;
  45 }
  46
  47 #if     LDBL_MANT_DIG == 53
  48 __strong_alias(ilogbl, ilogb);
  49 #endif  /* LDBL_MANT_DIG == 53 */