softfloat/f32_rem.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 The Regents of the University of California.
   8 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 float32_t f32_rem( float32_t a, float32_t b )
  45 {
  46     union ui32_f32 uA;
  47     uint_fast32_t uiA;
  48     bool signA;
  49     int_fast16_t expA;
  50     uint_fast32_t sigA;
  51     union ui32_f32 uB;
  52     uint_fast32_t uiB;
  53     int_fast16_t expB;
  54     uint_fast32_t sigB;
  55     struct exp16_sig32 normExpSig;
  56     uint32_t rem;
  57     int_fast16_t expDiff;
  58     uint32_t q, recip32, altRem, meanRem;
  59     bool signRem;
  60     uint_fast32_t uiZ;
  61     union ui32_f32 uZ;
  62
  63     /*------------------------------------------------------------------------
  64     *------------------------------------------------------------------------*/
  65     uA.f = a;
  66     uiA = uA.ui;
  67     signA = signF32UI( uiA );
  68     expA  = expF32UI( uiA );
  69     sigA  = fracF32UI( uiA );
  70     uB.f = b;
  71     uiB = uB.ui;
  72     expB = expF32UI( uiB );
  73     sigB = fracF32UI( uiB );
  74     /*------------------------------------------------------------------------
  75     *------------------------------------------------------------------------*/
  76     if ( expA == 0xFF ) {
  77         if ( sigA || ((expB == 0xFF) && sigB) ) goto propagateNaN;
  78         goto invalid;
  79     }
  80     if ( expB == 0xFF ) {
  81         if ( sigB ) goto propagateNaN;
  82         return a;
  83     }
  84     /*------------------------------------------------------------------------
  85     *------------------------------------------------------------------------*/
  86     if ( ! expB ) {
  87         if ( ! sigB ) goto invalid;
  88         normExpSig = softfloat_normSubnormalF32Sig( sigB );
  89         expB = normExpSig.exp;
  90         sigB = normExpSig.sig;
  91     }
  92     if ( ! expA ) {
  93         if ( ! sigA ) return a;
  94         normExpSig = softfloat_normSubnormalF32Sig( sigA );
  95         expA = normExpSig.exp;
  96         sigA = normExpSig.sig;
  97     }
  98     /*------------------------------------------------------------------------
  99     *------------------------------------------------------------------------*/
 100     rem = sigA | 0x00800000;
 101     sigB |= 0x00800000;
 102     expDiff = expA - expB;
 103     if ( expDiff < 1 ) {
 104         if ( expDiff < -1 ) return a;
 105         sigB <<= 6;
 106         if ( expDiff ) {
 107             rem <<= 5;
 108             q = 0;
 109         } else {
 110             rem <<= 6;
 111             q = (sigB <= rem);
 112             if ( q ) rem -= sigB;
 113         }
 114     } else {
 115         recip32 = softfloat_approxRecip32_1( sigB<<8 );
 116         /*--------------------------------------------------------------------
 117         | Changing the shift of `rem' here requires also changing the initial
 118         | subtraction from `expDiff'.
 119         *--------------------------------------------------------------------*/
 120         rem <<= 7;
 121         expDiff -= 31;
 122         /*--------------------------------------------------------------------
 123         | The scale of `sigB' affects how many bits are obtained during each
 124         | cycle of the loop.  Currently this is 29 bits per loop iteration,
 125         | which is believed to be the maximum possible.
 126         *--------------------------------------------------------------------*/
 127         sigB <<= 6;
 128         for (;;) {
 129             q = (rem * (uint_fast64_t) recip32)>>32;
 130             if ( expDiff < 0 ) break;
 131             rem = -(q * (uint32_t) sigB);
 132             expDiff -= 29;
 133         }
 134         /*--------------------------------------------------------------------
 135         | (`expDiff' cannot be less than -30 here.)
 136         *--------------------------------------------------------------------*/
 137         q >>= ~expDiff & 31;
 138         rem = (rem<<(expDiff + 30)) - q * (uint32_t) sigB;
 139     }
 140     /*------------------------------------------------------------------------
 141     *------------------------------------------------------------------------*/
 142     do {
 143         altRem = rem;
 144         ++q;
 145         rem -= sigB;
 146     } while ( ! (rem & 0x80000000) );
 147     meanRem = rem + altRem;
 148     if ( (meanRem & 0x80000000) || (! meanRem && (q & 1)) ) rem = altRem;
 149     signRem = signA;
 150     if ( 0x80000000 <= rem ) {
 151         signRem = ! signRem;
 152         rem = -rem;
 153     }
 154     return softfloat_normRoundPackToF32( signRem, expB, rem );
 155     /*------------------------------------------------------------------------
 156     *------------------------------------------------------------------------*/
 157  propagateNaN:
 158     uiZ = softfloat_propagateNaNF32UI( uiA, uiB );
 159     goto uiZ;
 160  invalid:
 161     softfloat_raiseFlags( softfloat_flag_invalid );
 162     uiZ = defaultNaNF32UI;
 163  uiZ:
 164     uZ.ui = uiZ;
 165     return uZ.f;
 166
 167 }
 168