softfloat/s_roundPackToF128.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 float128_t
  44  softfloat_roundPackToF128(
  45      bool sign,
  46      int_fast32_t exp,
  47      uint_fast64_t sig64,
  48      uint_fast64_t sig0,
  49      uint_fast64_t sigExtra
  50  )
  51 {
  52     uint_fast8_t roundingMode;
  53     bool roundNearEven, doIncrement, isTiny;
  54     struct uint128_extra sig128Extra;
  55     uint_fast64_t uiZ64, uiZ0;
  56     struct uint128 sig128;
  57     union ui128_f128 uZ;
  58
  59     /*------------------------------------------------------------------------
  60     *------------------------------------------------------------------------*/
  61     roundingMode = softfloat_roundingMode;
  62     roundNearEven = (roundingMode == softfloat_round_near_even);
  63     doIncrement = (UINT64_C( 0x8000000000000000 ) <= sigExtra);
  64     if ( ! roundNearEven && (roundingMode != softfloat_round_near_maxMag) ) {
  65         doIncrement =
  66             (roundingMode
  67                  == (sign ? softfloat_round_min : softfloat_round_max))
  68                 && sigExtra;
  69     }
  70     /*------------------------------------------------------------------------
  71     *------------------------------------------------------------------------*/
  72     if ( 0x7FFD <= (uint32_t) exp ) {
  73         if ( exp < 0 ) {
  74             /*----------------------------------------------------------------
  75             *----------------------------------------------------------------*/
  76             isTiny =
  77                    (softfloat_detectTininess
  78                         == softfloat_tininess_beforeRounding)
  79                 || (exp < -1)
  80                 || ! doIncrement
  81                 || softfloat_lt128(
  82                        sig64,
  83                        sig0,
  84                        UINT64_C( 0x0001FFFFFFFFFFFF ),
  85                        UINT64_C( 0xFFFFFFFFFFFFFFFF )
  86                    );
  87             sig128Extra =
  88                 softfloat_shiftRightJam128Extra( sig64, sig0, sigExtra, -exp );
  89             sig64 = sig128Extra.v.v64;
  90             sig0  = sig128Extra.v.v0;
  91             sigExtra = sig128Extra.extra;
  92             exp = 0;
  93             if ( isTiny && sigExtra ) {
  94                 softfloat_raiseFlags( softfloat_flag_underflow );
  95             }
  96             doIncrement = (UINT64_C( 0x8000000000000000 ) <= sigExtra);
  97             if (
  98                    ! roundNearEven
  99                 && (roundingMode != softfloat_round_near_maxMag)
 100             ) {
 101                 doIncrement =
 102                     (roundingMode
 103                          == (sign ? softfloat_round_min : softfloat_round_max))
 104                         && sigExtra;
 105             }
 106         } else if (
 107                (0x7FFD < exp)
 108             || ((exp == 0x7FFD)
 109                     && softfloat_eq128(
 110                            sig64,
 111                            sig0,
 112                            UINT64_C( 0x0001FFFFFFFFFFFF ),
 113                            UINT64_C( 0xFFFFFFFFFFFFFFFF )
 114                        )
 115                     && doIncrement)
 116         ) {
 117             /*----------------------------------------------------------------
 118             *----------------------------------------------------------------*/
 119             softfloat_raiseFlags(
 120                 softfloat_flag_overflow | softfloat_flag_inexact );
 121             if (
 122                    roundNearEven
 123                 || (roundingMode == softfloat_round_near_maxMag)
 124                 || (roundingMode
 125                         == (sign ? softfloat_round_min : softfloat_round_max))
 126             ) {
 127                 uiZ64 = packToF128UI64( sign, 0x7FFF, 0 );
 128                 uiZ0  = 0;
 129             } else {
 130                 uiZ64 =
 131                     packToF128UI64(
 132                         sign, 0x7FFE, UINT64_C( 0x0000FFFFFFFFFFFF ) );
 133                 uiZ0 = UINT64_C( 0xFFFFFFFFFFFFFFFF );
 134             }
 135             goto uiZ;
 136         }
 137     }
 138     /*------------------------------------------------------------------------
 139     *------------------------------------------------------------------------*/
 140     if ( sigExtra ) {
 141         softfloat_exceptionFlags |= softfloat_flag_inexact;
 142 #ifdef SOFTFLOAT_ROUND_ODD
 143         if ( roundingMode == softfloat_round_odd ) {
 144             sig0 |= 1;
 145             goto packReturn;
 146         }
 147 #endif
 148     }
 149     if ( doIncrement ) {
 150         sig128 = softfloat_add128( sig64, sig0, 0, 1 );
 151         sig64 = sig128.v64;
 152         sig0 =
 153             sig128.v0
 154                 & ~(uint64_t)
 155                        (! (sigExtra & UINT64_C( 0x7FFFFFFFFFFFFFFF ))
 156                             & roundNearEven);
 157     } else {
 158         if ( ! (sig64 | sig0) ) exp = 0;
 159     }
 160     /*------------------------------------------------------------------------
 161     *------------------------------------------------------------------------*/
 162  packReturn:
 163     uiZ64 = packToF128UI64( sign, exp, sig64 );
 164     uiZ0  = sig0;
 165  uiZ:
 166     uZ.ui.v64 = uiZ64;
 167     uZ.ui.v0  = uiZ0;
 168     return uZ.f;
 169
 170 }
 171