softfloat/s_subMagsF16.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, 2016, 2017 The Regents of the
   8 University of 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 float16_t softfloat_subMagsF16( uint_fast16_t uiA, uint_fast16_t uiB )
  45 {
  46     int_fast8_t expA;
  47     uint_fast16_t sigA;
  48     int_fast8_t expB;
  49     uint_fast16_t sigB;
  50     int_fast8_t expDiff;
  51     uint_fast16_t uiZ;
  52     int_fast16_t sigDiff;
  53     bool signZ;
  54     int_fast8_t shiftDist, expZ;
  55     uint_fast16_t sigZ, sigX, sigY;
  56     uint_fast32_t sig32Z;
  57     int_fast8_t roundingMode;
  58     union ui16_f16 uZ;
  59
  60     /*------------------------------------------------------------------------
  61     *------------------------------------------------------------------------*/
  62     expA = expF16UI( uiA );
  63     sigA = fracF16UI( uiA );
  64     expB = expF16UI( uiB );
  65     sigB = fracF16UI( uiB );
  66     /*------------------------------------------------------------------------
  67     *------------------------------------------------------------------------*/
  68     expDiff = expA - expB;
  69     if ( ! expDiff ) {
  70         /*--------------------------------------------------------------------
  71         *--------------------------------------------------------------------*/
  72         if ( expA == 0x1F ) {
  73             if ( sigA | sigB ) goto propagateNaN;
  74             softfloat_raiseFlags( softfloat_flag_invalid );
  75             uiZ = defaultNaNF16UI;
  76             goto uiZ;
  77         }
  78         sigDiff = sigA - sigB;
  79         if ( ! sigDiff ) {
  80             uiZ =
  81                 packToF16UI(
  82                     (softfloat_roundingMode == softfloat_round_min), 0, 0 );
  83             goto uiZ;
  84         }
  85         if ( expA ) --expA;
  86         signZ = signF16UI( uiA );
  87         if ( sigDiff < 0 ) {
  88             signZ = ! signZ;
  89             sigDiff = -sigDiff;
  90         }
  91         shiftDist = softfloat_countLeadingZeros16( sigDiff ) - 5;
  92         expZ = expA - shiftDist;
  93         if ( expZ < 0 ) {
  94             shiftDist = expA;
  95             expZ = 0;
  96         }
  97         sigZ = sigDiff<<shiftDist;
  98         goto pack;
  99     } else {
 100         /*--------------------------------------------------------------------
 101         *--------------------------------------------------------------------*/
 102         signZ = signF16UI( uiA );
 103         if ( expDiff < 0 ) {
 104             /*----------------------------------------------------------------
 105             *----------------------------------------------------------------*/
 106             signZ = ! signZ;
 107             if ( expB == 0x1F ) {
 108                 if ( sigB ) goto propagateNaN;
 109                 uiZ = packToF16UI( signZ, 0x1F, 0 );
 110                 goto uiZ;
 111             }
 112             if ( expDiff <= -13 ) {
 113                 uiZ = packToF16UI( signZ, expB, sigB );
 114                 if ( expA | sigA ) goto subEpsilon;
 115                 goto uiZ;
 116             }
 117             expZ = expA + 19;
 118             sigX = sigB | 0x0400;
 119             sigY = sigA + (expA ? 0x0400 : sigA);
 120             expDiff = -expDiff;
 121         } else {
 122             /*----------------------------------------------------------------
 123             *----------------------------------------------------------------*/
 124             uiZ = uiA;
 125             if ( expA == 0x1F ) {
 126                 if ( sigA ) goto propagateNaN;
 127                 goto uiZ;
 128             }
 129             if ( 13 <= expDiff ) {
 130                 if ( expB | sigB ) goto subEpsilon;
 131                 goto uiZ;
 132             }
 133             expZ = expB + 19;
 134             sigX = sigA | 0x0400;
 135             sigY = sigB + (expB ? 0x0400 : sigB);
 136         }
 137         sig32Z = ((uint_fast32_t) sigX<<expDiff) - sigY;
 138         shiftDist = softfloat_countLeadingZeros32( sig32Z ) - 1;
 139         sig32Z <<= shiftDist;
 140         expZ -= shiftDist;
 141         sigZ = sig32Z>>16;
 142         if ( sig32Z & 0xFFFF ) {
 143             sigZ |= 1;
 144         } else {
 145             if ( ! (sigZ & 0xF) && ((unsigned int) expZ < 0x1E) ) {
 146                 sigZ >>= 4;
 147                 goto pack;
 148             }
 149         }
 150         return softfloat_roundPackToF16( signZ, expZ, sigZ );
 151     }
 152     /*------------------------------------------------------------------------
 153     *------------------------------------------------------------------------*/
 154  propagateNaN:
 155     uiZ = softfloat_propagateNaNF16UI( uiA, uiB );
 156     goto uiZ;
 157     /*------------------------------------------------------------------------
 158     *------------------------------------------------------------------------*/
 159  subEpsilon:
 160     roundingMode = softfloat_roundingMode;
 161     if ( roundingMode != softfloat_round_near_even ) {
 162         if (
 163             (roundingMode == softfloat_round_minMag)
 164                 || (roundingMode
 165                         == (signF16UI( uiZ ) ? softfloat_round_max
 166                                 : softfloat_round_min))
 167         ) {
 168             --uiZ;
 169         }
 170 #ifdef SOFTFLOAT_ROUND_ODD
 171         else if ( roundingMode == softfloat_round_odd ) {
 172             uiZ = (uiZ - 1) | 1;
 173         }
 174 #endif
 175     }
 176     softfloat_exceptionFlags |= softfloat_flag_inexact;
 177     goto uiZ;
 178     /*------------------------------------------------------------------------
 179     *------------------------------------------------------------------------*/
 180  pack:
 181     uiZ = packToF16UI( signZ, expZ, sigZ );
 182  uiZ:
 183     uZ.ui = uiZ;
 184     return uZ.f;
 185
 186 }
 187