libm/s_ilogb.c

   1 /*
   2  * ====================================================
   3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   4  *
   5  * Developed at SunPro, a Sun Microsystems, Inc. business.
   6  * Permission to use, copy, modify, and distribute this
   7  * software is freely granted, provided that this notice
   8  * is preserved.
   9  * ====================================================
  10  */
  11
  12 /* ilogb(double x)
  13  * return the binary exponent of x
  14  * ilogb(+-0) = FP_ILOGB0
  15  * ilogb(+-inf) = INT_MAX
  16  * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
  17  */
  18
  19 #include "math.h"
  20 #include "math_private.h"
  21
  22 int ilogb(double x)
  23 {
  24         int32_t hx,lx,ix;
  25
  26         GET_HIGH_WORD(hx, x);
  27         hx &= 0x7fffffff;
  28
  29         if (hx < 0x00100000) {
  30                 GET_LOW_WORD(lx, x);
  31                 if ((hx|lx)==0)  /* +-0, ilogb(0) = FP_ILOGB0 */
  32                         return FP_ILOGB0;
  33                 /* subnormal x */
  34                 ix = -1043;
  35                 if (hx != 0) {
  36                         ix = -1022;
  37                         lx = (hx << 11);
  38                 }
  39                 /* each leading zero mantissa bit makes exponent smaller */
  40                 for (; lx > 0; lx <<= 1)
  41                         ix--;
  42                 return ix;
  43         }
  44
  45         if (hx < 0x7ff00000) /* normal x */
  46                 return (hx>>20) - 1023;
  47
  48         if (FP_ILOGBNAN != (~0U >> 1)) {
  49                 GET_LOW_WORD(lx, x);
  50                 if (hx == 0x7ff00000 && lx == 0)  /* +-inf */
  51                         return ~0U >> 1; /* = INT_MAX */
  52         }
  53
  54         /* NAN. ilogb(NAN) = FP_ILOGBNAN */
  55         return FP_ILOGBNAN;
  56 }
  57 libm_hidden_def(ilogb)