softfloat/s_roundPackToF64.c

   1
   2 /*============================================================================
   3
   4 This C source file is part of the SoftFloat IEEE Floating-Point Arithmetic
   5 Package, Release 3d, by John R. Hauser.
   6
   7 Copyright 2011, 2012, 2013, 2014, 2015, 2017 The Regents of the University of
   8 California.  All rights reserved.
   9
  10 Redistribution and use in source and binary forms, with or without
  11 modification, are permitted provided that the following conditions are met:
  12
  13  1. Redistributions of source code must retain the above copyright notice,
  14     this list of conditions, and the following disclaimer.
  15
  16  2. Redistributions in binary form must reproduce the above copyright notice,
  17     this list of conditions, and the following disclaimer in the documentation
  18     and/or other materials provided with the distribution.
  19
  20  3. Neither the name of the University nor the names of its contributors may
  21     be used to endorse or promote products derived from this software without
  22     specific prior written permission.
  23
  24 THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS "AS IS", AND ANY
  25 EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  26 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ARE
  27 DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
  28 DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  29 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  30 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  31 ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  32 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  33 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  34
  35 =============================================================================*/
  36
  37 #include <stdbool.h>
  38 #include <stdint.h>
  39 #include "platform.h"
  40 #include "internals.h"
  41 #include "softfloat.h"
  42
  43 float64_t
  44  softfloat_roundPackToF64( bool sign, int_fast16_t exp, uint_fast64_t sig )
  45 {
  46     uint_fast8_t roundingMode;
  47     bool roundNearEven;
  48     uint_fast16_t roundIncrement, roundBits;
  49     bool isTiny;
  50     uint_fast64_t uiZ;
  51     union ui64_f64 uZ;
  52
  53     /*------------------------------------------------------------------------
  54     *------------------------------------------------------------------------*/
  55     roundingMode = softfloat_roundingMode;
  56     roundNearEven = (roundingMode == softfloat_round_near_even);
  57     roundIncrement = 0x200;
  58     if ( ! roundNearEven && (roundingMode != softfloat_round_near_maxMag) ) {
  59         roundIncrement =
  60             (roundingMode
  61                  == (sign ? softfloat_round_min : softfloat_round_max))
  62                 ? 0x3FF
  63                 : 0;
  64     }
  65     roundBits = sig & 0x3FF;
  66     /*------------------------------------------------------------------------
  67     *------------------------------------------------------------------------*/
  68     if ( 0x7FD <= (uint16_t) exp ) {
  69         if ( exp < 0 ) {
  70             /*----------------------------------------------------------------
  71             *----------------------------------------------------------------*/
  72             isTiny =
  73                 (softfloat_detectTininess == softfloat_tininess_beforeRounding)
  74                     || (exp < -1)
  75                     || (sig + roundIncrement < UINT64_C( 0x8000000000000000 ));
  76             sig = softfloat_shiftRightJam64( sig, -exp );
  77             exp = 0;
  78             roundBits = sig & 0x3FF;
  79             if ( isTiny && roundBits ) {
  80                 softfloat_raiseFlags( softfloat_flag_underflow );
  81             }
  82         } else if (
  83             (0x7FD < exp)
  84                 || (UINT64_C( 0x8000000000000000 ) <= sig + roundIncrement)
  85         ) {
  86             /*----------------------------------------------------------------
  87             *----------------------------------------------------------------*/
  88             softfloat_raiseFlags(
  89                 softfloat_flag_overflow | softfloat_flag_inexact );
  90             uiZ = packToF64UI( sign, 0x7FF, 0 ) - ! roundIncrement;
  91             goto uiZ;
  92         }
  93     }
  94     /*------------------------------------------------------------------------
  95     *------------------------------------------------------------------------*/
  96     sig = (sig + roundIncrement)>>10;
  97     if ( roundBits ) {
  98         softfloat_exceptionFlags |= softfloat_flag_inexact;
  99 #ifdef SOFTFLOAT_ROUND_ODD
 100         if ( roundingMode == softfloat_round_odd ) {
 101             sig |= 1;
 102             goto packReturn;
 103         }
 104 #endif
 105     }
 106     sig &= ~(uint_fast64_t) (! (roundBits ^ 0x200) & roundNearEven);
 107     if ( ! sig ) exp = 0;
 108     /*------------------------------------------------------------------------
 109     *------------------------------------------------------------------------*/
 110  packReturn:
 111     uiZ = packToF64UI( sign, exp, sig );
 112  uiZ:
 113     uZ.ui = uiZ;
 114     return uZ.f;
 115
 116 }
 117