softfloat/s_subMagsF64.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 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 float64_t
  45  softfloat_subMagsF64( uint_fast64_t uiA, uint_fast64_t uiB, bool signZ )
  46 {
  47     int_fast16_t expA;
  48     uint_fast64_t sigA;
  49     int_fast16_t expB;
  50     uint_fast64_t sigB;
  51     int_fast16_t expDiff;
  52     uint_fast64_t uiZ;
  53     int_fast64_t sigDiff;
  54     int_fast8_t shiftDist;
  55     int_fast16_t expZ;
  56     uint_fast64_t sigZ;
  57     union ui64_f64 uZ;
  58
  59     /*------------------------------------------------------------------------
  60     *------------------------------------------------------------------------*/
  61     expA = expF64UI( uiA );
  62     sigA = fracF64UI( uiA );
  63     expB = expF64UI( uiB );
  64     sigB = fracF64UI( uiB );
  65     /*------------------------------------------------------------------------
  66     *------------------------------------------------------------------------*/
  67     expDiff = expA - expB;
  68     if ( ! expDiff ) {
  69         /*--------------------------------------------------------------------
  70         *--------------------------------------------------------------------*/
  71         if ( expA == 0x7FF ) {
  72             if ( sigA | sigB ) goto propagateNaN;
  73             softfloat_raiseFlags( softfloat_flag_invalid );
  74             uiZ = defaultNaNF64UI;
  75             goto uiZ;
  76         }
  77         sigDiff = sigA - sigB;
  78         if ( ! sigDiff ) {
  79             uiZ =
  80                 packToF64UI(
  81                     (softfloat_roundingMode == softfloat_round_min), 0, 0 );
  82             goto uiZ;
  83         }
  84         if ( expA ) --expA;
  85         if ( sigDiff < 0 ) {
  86             signZ = ! signZ;
  87             sigDiff = -sigDiff;
  88         }
  89         shiftDist = softfloat_countLeadingZeros64( sigDiff ) - 11;
  90         expZ = expA - shiftDist;
  91         if ( expZ < 0 ) {
  92             shiftDist = expA;
  93             expZ = 0;
  94         }
  95         uiZ = packToF64UI( signZ, expZ, sigDiff<<shiftDist );
  96         goto uiZ;
  97     } else {
  98         /*--------------------------------------------------------------------
  99         *--------------------------------------------------------------------*/
 100         sigA <<= 10;
 101         sigB <<= 10;
 102         if ( expDiff < 0 ) {
 103             /*----------------------------------------------------------------
 104             *----------------------------------------------------------------*/
 105             signZ = ! signZ;
 106             if ( expB == 0x7FF ) {
 107                 if ( sigB ) goto propagateNaN;
 108                 uiZ = packToF64UI( signZ, 0x7FF, 0 );
 109                 goto uiZ;
 110             }
 111             sigA += expA ? UINT64_C( 0x4000000000000000 ) : sigA;
 112             sigA = softfloat_shiftRightJam64( sigA, -expDiff );
 113             sigB |= UINT64_C( 0x4000000000000000 );
 114             expZ = expB;
 115             sigZ = sigB - sigA;
 116         } else {
 117             /*----------------------------------------------------------------
 118             *----------------------------------------------------------------*/
 119             if ( expA == 0x7FF ) {
 120                 if ( sigA ) goto propagateNaN;
 121                 uiZ = uiA;
 122                 goto uiZ;
 123             }
 124             sigB += expB ? UINT64_C( 0x4000000000000000 ) : sigB;
 125             sigB = softfloat_shiftRightJam64( sigB, expDiff );
 126             sigA |= UINT64_C( 0x4000000000000000 );
 127             expZ = expA;
 128             sigZ = sigA - sigB;
 129         }
 130         return softfloat_normRoundPackToF64( signZ, expZ - 1, sigZ );
 131     }
 132     /*------------------------------------------------------------------------
 133     *------------------------------------------------------------------------*/
 134  propagateNaN:
 135     uiZ = softfloat_propagateNaNF64UI( uiA, uiB );
 136  uiZ:
 137     uZ.ui = uiZ;
 138     return uZ.f;
 139
 140 }
 141