softfloat/f32_sqrt.c

   1
   2 /*============================================================================
   3
   4 This C source file is part of the SoftFloat IEEE Floating-Point Arithmetic
   5 Package, Release 3a, 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_sqrt( float32_t a )
  45 {
  46     union ui32_f32 uA;
  47     uint_fast32_t uiA;
  48     bool signA;
  49     int_fast16_t expA;
  50     uint_fast32_t sigA, uiZ;
  51     struct exp16_sig32 normExpSig;
  52     int_fast16_t expZ;
  53     uint_fast32_t sigZ, shiftedSigZ;
  54     uint32_t negRem;
  55     union ui32_f32 uZ;
  56
  57     /*------------------------------------------------------------------------
  58     *------------------------------------------------------------------------*/
  59     uA.f = a;
  60     uiA = uA.ui;
  61     signA = signF32UI( uiA );
  62     expA  = expF32UI( uiA );
  63     sigA  = fracF32UI( uiA );
  64     /*------------------------------------------------------------------------
  65     *------------------------------------------------------------------------*/
  66     if ( expA == 0xFF ) {
  67         if ( sigA ) {
  68             uiZ = softfloat_propagateNaNF32UI( uiA, 0 );
  69             goto uiZ;
  70         }
  71         if ( ! signA ) return a;
  72         goto invalid;
  73     }
  74     /*------------------------------------------------------------------------
  75     *------------------------------------------------------------------------*/
  76     if ( signA ) {
  77         if ( ! (expA | sigA) ) return a;
  78         goto invalid;
  79     }
  80     /*------------------------------------------------------------------------
  81     *------------------------------------------------------------------------*/
  82     if ( ! expA ) {
  83         if ( ! sigA ) return a;
  84         normExpSig = softfloat_normSubnormalF32Sig( sigA );
  85         expA = normExpSig.exp;
  86         sigA = normExpSig.sig;
  87     }
  88     /*------------------------------------------------------------------------
  89     *------------------------------------------------------------------------*/
  90     expZ = ((expA - 0x7F)>>1) + 0x7E;
  91     expA &= 1;
  92     sigA = (sigA | 0x00800000)<<8;
  93     sigZ =
  94         ((uint_fast64_t) sigA * softfloat_approxRecipSqrt32_1( expA, sigA ))
  95             >>32;
  96     if ( expA ) sigZ >>= 1;
  97     sigZ += 2;
  98     /*------------------------------------------------------------------------
  99     *------------------------------------------------------------------------*/
 100     if ( (sigZ & 0x3F) < 2 ) {
 101         shiftedSigZ = sigZ>>2;
 102         negRem = shiftedSigZ * shiftedSigZ;
 103         sigZ = shiftedSigZ<<2;
 104         if ( negRem & 0x80000000 ) {
 105             sigZ |= 1;
 106         } else {
 107             if ( negRem ) --sigZ;
 108         }
 109     }
 110     return softfloat_roundPackToF32( 0, expZ, sigZ );
 111     /*------------------------------------------------------------------------
 112     *------------------------------------------------------------------------*/
 113  invalid:
 114     softfloat_raiseFlags( softfloat_flag_invalid );
 115     uiZ = defaultNaNF32UI;
 116  uiZ:
 117     uZ.ui = uiZ;
 118     return uZ.f;
 119
 120 }
 121