softfloat/f128_roundToInt.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, 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 float128_t
  45  f128_roundToInt( float128_t a, uint_fast8_t roundingMode, bool exact )
  46 {
  47     union ui128_f128 uA;
  48     uint_fast64_t uiA64, uiA0;
  49     int_fast32_t exp;
  50     struct uint128 uiZ;
  51     uint_fast64_t lastBitMask, roundBitsMask;
  52     bool roundNearEven;
  53     union ui128_f128 uZ;
  54
  55     /*------------------------------------------------------------------------
  56     *------------------------------------------------------------------------*/
  57     uA.f = a;
  58     uiA64 = uA.ui.v64;
  59     uiA0  = uA.ui.v0;
  60     exp = expF128UI64( uiA64 );
  61     /*------------------------------------------------------------------------
  62     *------------------------------------------------------------------------*/
  63     if ( 0x402F <= exp ) {
  64         /*--------------------------------------------------------------------
  65         *--------------------------------------------------------------------*/
  66         if ( 0x406F <= exp ) {
  67             if ( (exp == 0x7FFF) && (fracF128UI64( uiA64 ) | uiA0) ) {
  68                 uiZ = softfloat_propagateNaNF128UI( uiA64, uiA0, 0, 0 );
  69                 goto uiZ;
  70             }
  71             return a;
  72         }
  73         /*--------------------------------------------------------------------
  74         *--------------------------------------------------------------------*/
  75         lastBitMask = (uint_fast64_t) 2<<(0x406E - exp);
  76         roundBitsMask = lastBitMask - 1;
  77         uiZ.v64 = uiA64;
  78         uiZ.v0  = uiA0;
  79         roundNearEven = (roundingMode == softfloat_round_near_even);
  80         if ( roundNearEven || (roundingMode == softfloat_round_near_maxMag) ) {
  81             if ( exp == 0x402F ) {
  82                 if ( UINT64_C( 0x8000000000000000 ) <= uiZ.v0 ) {
  83                     ++uiZ.v64;
  84                     if (
  85                         roundNearEven
  86                             && (uiZ.v0 == UINT64_C( 0x8000000000000000 ))
  87                     ) {
  88                         uiZ.v64 &= ~1;
  89                     }
  90                 }
  91             } else {
  92                 uiZ = softfloat_add128( uiZ.v64, uiZ.v0, 0, lastBitMask>>1 );
  93                 if ( roundNearEven && ! (uiZ.v0 & roundBitsMask) ) {
  94                     uiZ.v0 &= ~lastBitMask;
  95                 }
  96             }
  97         } else if (
  98             roundingMode
  99                 == (signF128UI64( uiZ.v64 ) ? softfloat_round_min
 100                         : softfloat_round_max)
 101         ) {
 102             uiZ = softfloat_add128( uiZ.v64, uiZ.v0, 0, roundBitsMask );
 103         }
 104         uiZ.v0 &= ~roundBitsMask;
 105     } else {
 106         /*--------------------------------------------------------------------
 107         *--------------------------------------------------------------------*/
 108         if ( exp < 0x3FFF ) {
 109             if ( ! ((uiA64 & UINT64_C( 0x7FFFFFFFFFFFFFFF )) | uiA0) ) {
 110                 return a;
 111             }
 112             if ( exact ) softfloat_exceptionFlags |= softfloat_flag_inexact;
 113             uiZ.v64 = uiA64 & packToF128UI64( 1, 0, 0 );
 114             uiZ.v0  = 0;
 115             switch ( roundingMode ) {
 116              case softfloat_round_near_even:
 117                 if ( ! (fracF128UI64( uiA64 ) | uiA0) ) break;
 118              case softfloat_round_near_maxMag:
 119                 if ( exp == 0x3FFE ) uiZ.v64 |= packToF128UI64( 0, 0x3FFF, 0 );
 120                 break;
 121              case softfloat_round_min:
 122                 if ( uiZ.v64 ) uiZ.v64 = packToF128UI64( 1, 0x3FFF, 0 );
 123                 break;
 124              case softfloat_round_max:
 125                 if ( ! uiZ.v64 ) uiZ.v64 = packToF128UI64( 0, 0x3FFF, 0 );
 126                 break;
 127             }
 128             goto uiZ;
 129         }
 130         /*--------------------------------------------------------------------
 131         *--------------------------------------------------------------------*/
 132         uiZ.v64 = uiA64;
 133         uiZ.v0  = 0;
 134         lastBitMask = (uint_fast64_t) 1<<(0x402F - exp);
 135         roundBitsMask = lastBitMask - 1;
 136         if ( roundingMode == softfloat_round_near_maxMag ) {
 137             uiZ.v64 += lastBitMask>>1;
 138         } else if ( roundingMode == softfloat_round_near_even ) {
 139             uiZ.v64 += lastBitMask>>1;
 140             if ( ! ((uiZ.v64 & roundBitsMask) | uiA0) ) {
 141                 uiZ.v64 &= ~lastBitMask;
 142             }
 143         } else if (
 144             roundingMode
 145                 == (signF128UI64( uiZ.v64 ) ? softfloat_round_min
 146                         : softfloat_round_max)
 147         ) {
 148             uiZ.v64 = (uiZ.v64 | (uiA0 != 0)) + roundBitsMask;
 149         }
 150         uiZ.v64 &= ~roundBitsMask;
 151     }
 152     if ( exact && ((uiZ.v64 != uiA64) || (uiZ.v0 != uiA0)) ) {
 153         softfloat_exceptionFlags |= softfloat_flag_inexact;
 154     }
 155  uiZ:
 156     uZ.ui = uiZ;
 157     return uZ.f;
 158
 159 }
 160