github.com/igggame/nebulas-go@v2.1.0+incompatible/nbre/3rd_party/SoftFloat-3e/source/f16_rem.c (about)

     1  
     2  /*============================================================================
     3  
     4  This C source file is part of the SoftFloat IEEE Floating-Point Arithmetic
     5  Package, Release 3e, 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  float16_t f16_rem( float16_t a, float16_t b )
    45  {
    46      union ui16_f16 uA;
    47      uint_fast16_t uiA;
    48      bool signA;
    49      int_fast8_t expA;
    50      uint_fast16_t sigA;
    51      union ui16_f16 uB;
    52      uint_fast16_t uiB;
    53      int_fast8_t expB;
    54      uint_fast16_t sigB;
    55      struct exp8_sig16 normExpSig;
    56      uint16_t rem;
    57      int_fast8_t expDiff;
    58      uint_fast16_t q;
    59      uint32_t recip32, q32;
    60      uint16_t altRem, meanRem;
    61      bool signRem;
    62      uint_fast16_t uiZ;
    63      union ui16_f16 uZ;
    64  
    65      /*------------------------------------------------------------------------
    66      *------------------------------------------------------------------------*/
    67      uA.f = a;
    68      uiA = uA.ui;
    69      signA = signF16UI( uiA );
    70      expA  = expF16UI( uiA );
    71      sigA  = fracF16UI( uiA );
    72      uB.f = b;
    73      uiB = uB.ui;
    74      expB = expF16UI( uiB );
    75      sigB = fracF16UI( uiB );
    76      /*------------------------------------------------------------------------
    77      *------------------------------------------------------------------------*/
    78      if ( expA == 0x1F ) {
    79          if ( sigA || ((expB == 0x1F) && sigB) ) goto propagateNaN;
    80          goto invalid;
    81      }
    82      if ( expB == 0x1F ) {
    83          if ( sigB ) goto propagateNaN;
    84          return a;
    85      }
    86      /*------------------------------------------------------------------------
    87      *------------------------------------------------------------------------*/
    88      if ( ! expB ) {
    89          if ( ! sigB ) goto invalid;
    90          normExpSig = softfloat_normSubnormalF16Sig( sigB );
    91          expB = normExpSig.exp;
    92          sigB = normExpSig.sig;
    93      }
    94      if ( ! expA ) {
    95          if ( ! sigA ) return a;
    96          normExpSig = softfloat_normSubnormalF16Sig( sigA );
    97          expA = normExpSig.exp;
    98          sigA = normExpSig.sig;
    99      }
   100      /*------------------------------------------------------------------------
   101      *------------------------------------------------------------------------*/
   102      rem = sigA | 0x0400;
   103      sigB |= 0x0400;
   104      expDiff = expA - expB;
   105      if ( expDiff < 1 ) {
   106          if ( expDiff < -1 ) return a;
   107          sigB <<= 3;
   108          if ( expDiff ) {
   109              rem <<= 2;
   110              q = 0;
   111          } else {
   112              rem <<= 3;
   113              q = (sigB <= rem);
   114              if ( q ) rem -= sigB;
   115          }
   116      } else {
   117          recip32 = softfloat_approxRecip32_1( (uint_fast32_t) sigB<<21 );
   118          /*--------------------------------------------------------------------
   119          | Changing the shift of `rem' here requires also changing the initial
   120          | subtraction from `expDiff'.
   121          *--------------------------------------------------------------------*/
   122          rem <<= 4;
   123          expDiff -= 31;
   124          /*--------------------------------------------------------------------
   125          | The scale of `sigB' affects how many bits are obtained during each
   126          | cycle of the loop.  Currently this is 29 bits per loop iteration,
   127          | which is believed to be the maximum possible.
   128          *--------------------------------------------------------------------*/
   129          sigB <<= 3;
   130          for (;;) {
   131              q32 = (rem * (uint_fast64_t) recip32)>>16;
   132              if ( expDiff < 0 ) break;
   133              rem = -((uint_fast16_t) q32 * sigB);
   134              expDiff -= 29;
   135          }
   136          /*--------------------------------------------------------------------
   137          | (`expDiff' cannot be less than -30 here.)
   138          *--------------------------------------------------------------------*/
   139          q32 >>= ~expDiff & 31;
   140          q = q32;
   141          rem = (rem<<(expDiff + 30)) - q * sigB;
   142      }
   143      /*------------------------------------------------------------------------
   144      *------------------------------------------------------------------------*/
   145      do {
   146          altRem = rem;
   147          ++q;
   148          rem -= sigB;
   149      } while ( ! (rem & 0x8000) );
   150      meanRem = rem + altRem;
   151      if ( (meanRem & 0x8000) || (! meanRem && (q & 1)) ) rem = altRem;
   152      signRem = signA;
   153      if ( 0x8000 <= rem ) {
   154          signRem = ! signRem;
   155          rem = -rem;
   156      }
   157      return softfloat_normRoundPackToF16( signRem, expB, rem );
   158      /*------------------------------------------------------------------------
   159      *------------------------------------------------------------------------*/
   160   propagateNaN:
   161      uiZ = softfloat_propagateNaNF16UI( uiA, uiB );
   162      goto uiZ;
   163   invalid:
   164      softfloat_raiseFlags( softfloat_flag_invalid );
   165      uiZ = defaultNaNF16UI;
   166   uiZ:
   167      uZ.ui = uiZ;
   168      return uZ.f;
   169  
   170  }
   171