libgcc/config/libbid/bid64_scalb.c

   1 /* Copyright (C) 2007  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 2, or (at your option) any later
   8 version.
   9
  10 In addition to the permissions in the GNU General Public License, the
  11 Free Software Foundation gives you unlimited permission to link the
  12 compiled version of this file into combinations with other programs,
  13 and to distribute those combinations without any restriction coming
  14 from the use of this file.  (The General Public License restrictions
  15 do apply in other respects; for example, they cover modification of
  16 the file, and distribution when not linked into a combine
  17 executable.)
  18
  19 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  20 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  21 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  22 for more details.
  23
  24 You should have received a copy of the GNU General Public License
  25 along with GCC; see the file COPYING.  If not, write to the Free
  26 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
  27 02110-1301, USA.  */
  28
  29 #include "bid_internal.h"
  30
  31 #define MAX_FORMAT_DIGITS     16
  32 #define DECIMAL_EXPONENT_BIAS 398
  33 #define MAX_DECIMAL_EXPONENT  767
  34
  35 #if DECIMAL_CALL_BY_REFERENCE
  36
  37 void
  38 __bid64_scalb (UINT64 * pres, UINT64 * px,
  39              int *pn _RND_MODE_PARAM _EXC_FLAGS_PARAM _EXC_MASKS_PARAM
  40              _EXC_INFO_PARAM) {
  41   UINT64 x;
  42   int n;
  43 #else
  44
  45 UINT64
  46 __bid64_scalb (UINT64 x,
  47              int n _RND_MODE_PARAM _EXC_FLAGS_PARAM _EXC_MASKS_PARAM
  48              _EXC_INFO_PARAM) {
  49 #endif
  50   UINT64 sign_x, coefficient_x, res;
  51   int exponent_x, rmode;
  52
  53 #if DECIMAL_CALL_BY_REFERENCE
  54 #if !DECIMAL_GLOBAL_ROUNDING
  55   _IDEC_round rnd_mode = *prnd_mode;
  56 #endif
  57   x = *px;
  58   n = *pn;
  59 #endif
  60
  61   // unpack arguments, check for NaN or Infinity
  62   if (!unpack_BID64 (&sign_x, &exponent_x, &coefficient_x, x)) {
  63     // x is Inf. or NaN or 0
  64     res = x;
  65     BID_RETURN (res);
  66   }
  67
  68   exponent_x += n;
  69
  70   if ((UINT32) exponent_x <= MAX_DECIMAL_EXPONENT) {
  71     res = very_fast_get_BID64 (sign_x, exponent_x, coefficient_x);
  72     BID_RETURN (res);
  73   }
  74   // check for overflow
  75   if (exponent_x > MAX_DECIMAL_EXPONENT) {
  76     // try to normalize coefficient
  77     while ((coefficient_x < 1000000000000000ull)
  78            && (exponent_x > MAX_DECIMAL_EXPONENT)) {
  79       // coefficient_x < 10^15, scale by 10
  80       coefficient_x = (coefficient_x << 1) + (coefficient_x << 3);
  81       exponent_x--;
  82     }
  83     if (exponent_x <= MAX_DECIMAL_EXPONENT) {
  84       res = very_fast_get_BID64 (sign_x, exponent_x, coefficient_x);
  85       BID_RETURN (res);
  86     }
  87   }
  88   // exponent < 0
  89   // the BID pack routine will round the coefficient
  90   rmode = rnd_mode;
  91   res = get_BID64 (sign_x, exponent_x, coefficient_x, rmode, pfpsf);
  92   BID_RETURN (res);
  93
  94 }