libgcc/config/libbid/bid128_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 #define BID_128RES
  25 #include "bid_internal.h"
  26
  27 BID128_FUNCTION_ARG1_NORND_CUSTOMRESTYPE(int, bid128_logb, x)
  28
  29   UINT128 CX;
  30   UINT64 sign_x;
  31   SINT64 D;
  32   int_float f64, fx;
  33   int exponent_x, bin_expon_cx, digits;
  34
  35   if (!unpack_BID128_value (&sign_x, &exponent_x, &CX, x)) {
  36 #ifdef SET_STATUS_FLAGS
  37       __set_status_flags (pfpsf, INVALID_EXCEPTION);
  38 #endif
  39     BID_RETURN_VAL (0x80000000);
  40   }
  41   // find number of digits in coefficient
  42   // 2^64
  43   f64.i = 0x5f800000;
  44   // fx ~ CX
  45   fx.d = (float) CX.w[1] * f64.d + (float) CX.w[0];
  46   bin_expon_cx = ((fx.i >> 23) & 0xff) - 0x7f;
  47   digits = estimate_decimal_digits[bin_expon_cx];
  48   // scale = 38-estimate_decimal_digits[bin_expon_cx];
  49   D = CX.w[1] - power10_index_binexp_128[bin_expon_cx].w[1];
  50   if (D > 0 || (!D && CX.w[0] >= power10_index_binexp_128[bin_expon_cx].w[0])) {
  51     digits++;
  52   }
  53
  54   exponent_x = exponent_x - DECIMAL_EXPONENT_BIAS_128 - 1 + digits;
  55
  56   BID_RETURN_VAL (exponent_x);
  57
  58 }