sysdeps/powerpc/power7/fpu/s_logbl.c

   1 /* logbl(). PowerPC/POWER7 version.
   2    Copyright (C) 2012-2014 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <math.h>
  20 #include <math_private.h>
  21 #include <math_ldbl_opt.h>
  22
  23 /* This implementation avoids FP to INT conversions by using VSX
  24    bitwise instructions over FP values.  */
  25
  26 static const double two1div52 = 2.220446049250313e-16;  /* 1/2**52  */
  27 static const double two10m1   = -1023.0;                /* 2**10 -1  */
  28
  29 /* FP mask to extract the exponent.  */
  30 static const union {
  31   unsigned long long mask;
  32   double d;
  33 } mask = { 0x7ff0000000000000ULL };
  34
  35 long double
  36 __logbl (long double x)
  37 {
  38   double xh;
  39   double ret;
  40
  41   if (__builtin_expect (x == 0.0L, 0))
  42     /* Raise FE_DIVBYZERO and return -HUGE_VAL[LF].  */
  43     return -1.0L / __builtin_fabsl (x);
  44
  45   xh = ldbl_high (x);
  46   /* ret = x & 0x7ff0000000000000;  */
  47   asm (
  48     "xxland %x0,%x1,%x2\n"
  49     "fcfid  %0,%0"
  50     : "=f" (ret)
  51     : "f" (xh), "f" (mask.d));
  52   /* ret = (ret >> 52) - 1023.0;  */
  53   ret = (ret * two1div52) + two10m1;
  54   if (__builtin_expect (ret > -two10m1, 0))
  55     /* Multiplication is used to set logb (+-INF) = INF.  */
  56     return (xh * xh);
  57   else if (__builtin_expect (ret == two10m1, 0))
  58     {
  59       /* POSIX specifies that denormal number is treated as
  60          though it were normalized.  */
  61       int64_t hx;
  62
  63       EXTRACT_WORDS64 (hx, xh);
  64       return (long double) (-1023 - (__builtin_clzll (hx) - 12));
  65     }
  66   /* Test to avoid logb_downward (0.0) == -0.0.  */
  67   return ret == -0.0 ? 0.0 : ret;
  68 }
  69 #ifndef __logbl
  70 long_double_symbol (libm, __logbl, logbl);
  71 #endif