softfloat/source/extF80_roundToInt.c

   1
   2 /*============================================================================
   3
   4 This C source file is part of the SoftFloat IEEE Floating-Point Arithmetic
   5 Package, Release 3e, by John R. Hauser.
   6
   7 Copyright 2011, 2012, 2013, 2014, 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 "specialize.h"
  42 #include "softfloat.h"
  43
  44 extFloat80_t
  45  extF80_roundToInt( extFloat80_t a, uint_fast8_t roundingMode, bool exact )
  46 {
  47     union { struct extFloat80M s; extFloat80_t f; } uA;
  48     uint_fast16_t uiA64, signUI64;
  49     int_fast32_t exp;
  50     uint_fast64_t sigA;
  51     uint_fast16_t uiZ64;
  52     uint_fast64_t sigZ;
  53     struct exp32_sig64 normExpSig;
  54     struct uint128 uiZ;
  55     uint_fast64_t lastBitMask, roundBitsMask;
  56     union { struct extFloat80M s; extFloat80_t f; } uZ;
  57
  58     /*------------------------------------------------------------------------
  59     *------------------------------------------------------------------------*/
  60     uA.f = a;
  61     uiA64 = uA.s.signExp;
  62     signUI64 = uiA64 & packToExtF80UI64( 1, 0 );
  63     exp = expExtF80UI64( uiA64 );
  64     sigA = uA.s.signif;
  65     /*------------------------------------------------------------------------
  66     *------------------------------------------------------------------------*/
  67     if ( !(sigA & UINT64_C( 0x8000000000000000 )) && (exp != 0x7FFF) ) {
  68         if ( !sigA ) {
  69             uiZ64 = signUI64;
  70             sigZ = 0;
  71             goto uiZ;
  72         }
  73         normExpSig = softfloat_normSubnormalExtF80Sig( sigA );
  74         exp += normExpSig.exp;
  75         sigA = normExpSig.sig;
  76     }
  77     /*------------------------------------------------------------------------
  78     *------------------------------------------------------------------------*/
  79     if ( 0x403E <= exp ) {
  80         if ( exp == 0x7FFF ) {
  81             if ( sigA & UINT64_C( 0x7FFFFFFFFFFFFFFF ) ) {
  82                 uiZ = softfloat_propagateNaNExtF80UI( uiA64, sigA, 0, 0 );
  83                 uiZ64 = uiZ.v64;
  84                 sigZ  = uiZ.v0;
  85                 goto uiZ;
  86             }
  87             sigZ = UINT64_C( 0x8000000000000000 );
  88         } else {
  89             sigZ = sigA;
  90         }
  91         uiZ64 = signUI64 | exp;
  92         goto uiZ;
  93     }
  94     if ( exp <= 0x3FFE ) {
  95         if ( exact ) softfloat_exceptionFlags |= softfloat_flag_inexact;
  96         switch ( roundingMode ) {
  97          case softfloat_round_near_even:
  98             if ( !(sigA & UINT64_C( 0x7FFFFFFFFFFFFFFF )) ) break;
  99          case softfloat_round_near_maxMag:
 100             if ( exp == 0x3FFE ) goto mag1;
 101             break;
 102          case softfloat_round_min:
 103             if ( signUI64 ) goto mag1;
 104             break;
 105          case softfloat_round_max:
 106             if ( !signUI64 ) goto mag1;
 107             break;
 108 #ifdef SOFTFLOAT_ROUND_ODD
 109          case softfloat_round_odd:
 110             goto mag1;
 111 #endif
 112         }
 113         uiZ64 = signUI64;
 114         sigZ  = 0;
 115         goto uiZ;
 116      mag1:
 117         uiZ64 = signUI64 | 0x3FFF;
 118         sigZ  = UINT64_C( 0x8000000000000000 );
 119         goto uiZ;
 120     }
 121     /*------------------------------------------------------------------------
 122     *------------------------------------------------------------------------*/
 123     uiZ64 = signUI64 | exp;
 124     lastBitMask = (uint_fast64_t) 1<<(0x403E - exp);
 125     roundBitsMask = lastBitMask - 1;
 126     sigZ = sigA;
 127     if ( roundingMode == softfloat_round_near_maxMag ) {
 128         sigZ += lastBitMask>>1;
 129     } else if ( roundingMode == softfloat_round_near_even ) {
 130         sigZ += lastBitMask>>1;
 131         if ( !(sigZ & roundBitsMask) ) sigZ &= ~lastBitMask;
 132     } else if (
 133         roundingMode == (signUI64 ? softfloat_round_min : softfloat_round_max)
 134     ) {
 135         sigZ += roundBitsMask;
 136     }
 137     sigZ &= ~roundBitsMask;
 138     if ( !sigZ ) {
 139         ++uiZ64;
 140         sigZ = UINT64_C( 0x8000000000000000 );
 141     }
 142     if ( sigZ != sigA ) {
 143 #ifdef SOFTFLOAT_ROUND_ODD
 144         if ( roundingMode == softfloat_round_odd ) sigZ |= lastBitMask;
 145 #endif
 146         if ( exact ) softfloat_exceptionFlags |= softfloat_flag_inexact;
 147     }
 148  uiZ:
 149     uZ.s.signExp = uiZ64;
 150     uZ.s.signif = sigZ;
 151     return uZ.f;
 152
 153 }
 154