libgcc/config/libbid/bid64_logb.c

   1 /* Copyright (C) 2007-2017 Free Software Foundation, Inc.
   2
   3 This file is part of GCC.
   4
   5 GCC is free software; you can redistribute it and/or modify it under
   6 the terms of the GNU General Public License as published by the Free
   7 Software Foundation; either version 3, or (at your option) any later
   8 version.
   9
  10 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  11 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  13 for more details.
  14
  15 Under Section 7 of GPL version 3, you are granted additional
  16 permissions described in the GCC Runtime Library Exception, version
  17 3.1, as published by the Free Software Foundation.
  18
  19 You should have received a copy of the GNU General Public License and
  20 a copy of the GCC Runtime Library Exception along with this program;
  21 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  22 <http://www.gnu.org/licenses/>.  */
  23
  24 #include "bid_internal.h"
  25
  26 #define MAX_FORMAT_DIGITS     16
  27 #define DECIMAL_EXPONENT_BIAS 398
  28
  29 #if DECIMAL_CALL_BY_REFERENCE
  30
  31 void
  32 bid64_logb (int * pres, UINT64 * px
  33             _EXC_FLAGS_PARAM _EXC_MASKS_PARAM _EXC_INFO_PARAM) {
  34   UINT64 x;
  35 #else
  36
  37 int
  38 bid64_logb (UINT64 x _EXC_FLAGS_PARAM _EXC_MASKS_PARAM _EXC_INFO_PARAM) {
  39 #endif
  40   UINT64 sign_x, coefficient_x;
  41   int_double dx;
  42   int exponent_x, bin_expon_cx, digits;
  43
  44 #if DECIMAL_CALL_BY_REFERENCE
  45   x = *px;
  46 #endif
  47   // unpack arguments, check for NaN or Infinity
  48   if (!unpack_BID64 (&sign_x, &exponent_x, &coefficient_x, x)) {
  49     // x is Inf. or NaN
  50 #ifdef SET_STATUS_FLAGS
  51       __set_status_flags (pfpsf, INVALID_EXCEPTION);
  52 #endif
  53       BID_RETURN (0x80000000);
  54   }
  55   // find number of digits in coefficient
  56   if (coefficient_x >= 1000000000000000ull) {
  57     digits = 16;
  58   } else {
  59     dx.d = (double)coefficient_x;   // exact conversion;
  60     bin_expon_cx = (int)(dx.i >> 52) - 1023;
  61     digits = estimate_decimal_digits[bin_expon_cx];
  62     if (coefficient_x >= power10_table_128[digits].w[0])
  63       digits++;
  64   }
  65   exponent_x = exponent_x - DECIMAL_EXPONENT_BIAS + digits - 1;
  66
  67   BID_RETURN (exponent_x);
  68 }