sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c

   1 /* s_ilogbl.c -- long double version of s_ilogb.c.
   2  * Conversion to IEEE quad long double by Jakub Jelinek, jj@ultra.linux.cz.
   3  */
   4
   5 /*
   6  * ====================================================
   7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   8  *
   9  * Developed at SunPro, a Sun Microsystems, Inc. business.
  10  * Permission to use, copy, modify, and distribute this
  11  * software is freely granted, provided that this notice
  12  * is preserved.
  13  * ====================================================
  14  */
  15
  16 #if defined(LIBM_SCCS) && !defined(lint)
  17 static char rcsid[] = "$NetBSD: $";
  18 #endif
  19
  20 /* ilogbl(long double x)
  21  * return the binary exponent of non-zero x
  22  * ilogbl(0) = FP_ILOGB0
  23  * ilogbl(NaN) = FP_ILOGBNAN (no signal is raised)
  24  * ilogbl(+-Inf) = INT_MAX (no signal is raised)
  25  */
  26
  27 #include <limits.h>
  28 #include <math.h>
  29 #include <math_private.h>
  30 #include <math_ldbl_opt.h>
  31
  32 int __ieee754_ilogbl(long double x)
  33 {
  34         int64_t hx, hxs;
  35         int ix;
  36         double xhi, xlo;
  37
  38         ldbl_unpack (x, &xhi, &xlo);
  39         EXTRACT_WORDS64 (hx, xhi);
  40         hxs = hx;
  41         hx &= 0x7fffffffffffffffLL;
  42         if(hx <= 0x0010000000000000LL) {
  43             if(hx==0)
  44                 return FP_ILOGB0;       /* ilogbl(0) = FP_ILOGB0 */
  45             else                        /* subnormal x */
  46                 for (ix = -1022, hx<<=11; hx>0; hx<<=1) ix -=1;
  47             return ix;
  48         }
  49         else if (hx < 0x7ff0000000000000LL)
  50           {
  51             int hexp = (hx >> 52) - 0x3ff;
  52             /* If the high part is a power of 2, and the low part is
  53                nonzero with the opposite sign, the low part affects
  54                the exponent.  */
  55             if ((hx & 0x000fffffffffffffLL) == 0)
  56               {
  57                 int64_t lx;
  58                 EXTRACT_WORDS64 (lx, xlo);
  59                 if ((hxs ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0)
  60                   hexp--;
  61               }
  62             return hexp;
  63           }
  64         else if (FP_ILOGBNAN != INT_MAX) {
  65             /* ISO C99 requires ilogbl(+-Inf) == INT_MAX.  */
  66             if (hx==0x7ff0000000000000LL)
  67                 return INT_MAX;
  68         }
  69         return FP_ILOGBNAN;
  70 }