softfloat/f64_sqrt.c

   1
   2 #include <stdbool.h>
   3 #include <stdint.h>
   4 #include "platform.h"
   5 #include "primitives.h"
   6 #include "internals.h"
   7 #include "specialize.h"
   8 #include "softfloat.h"
   9
  10 float64_t f64_sqrt( float64_t a )
  11 {
  12     union ui64_f64 uA;
  13     uint_fast64_t uiA;
  14     bool signA;
  15     int_fast16_t expA;
  16     uint_fast64_t sigA, uiZ;
  17     struct exp16_sig64 normExpSig;
  18     int_fast16_t expZ;
  19     uint_fast32_t sigZ32;
  20     uint_fast64_t sigZ;
  21     struct uint128 term, rem;
  22     union ui64_f64 uZ;
  23
  24     uA.f = a;
  25     uiA = uA.ui;
  26     signA = signF64UI( uiA );
  27     expA = expF64UI( uiA );
  28     sigA = fracF64UI( uiA );
  29     if ( expA == 0x7FF ) {
  30         if ( sigA ) {
  31             uiZ = softfloat_propagateNaNF64UI( uiA, 0 );
  32             goto uiZ;
  33         }
  34         if ( ! signA ) return a;
  35         goto invalid;
  36     }
  37     if ( signA ) {
  38         if ( ! ( expA | sigA ) ) return a;
  39         goto invalid;
  40     }
  41     if ( ! expA ) {
  42         if ( ! sigA ) return a;
  43         normExpSig = softfloat_normSubnormalF64Sig( sigA );
  44         expA = normExpSig.exp;
  45         sigA = normExpSig.sig;
  46     }
  47     expZ = ( ( expA - 0x3FF )>>1 ) + 0x3FE;
  48     sigA |= UINT64_C( 0x0010000000000000 );
  49     sigZ32 = softfloat_estimateSqrt32( expA, sigA>>21 );
  50     sigA <<= 9 - ( expA & 1 );
  51     sigZ =
  52         softfloat_estimateDiv128To64( sigA, 0, (uint_fast64_t) sigZ32<<32 )
  53             + ( (uint_fast64_t) sigZ32<<30 );
  54     if ( ( sigZ & 0x1FF ) <= 5 ) {
  55         term = softfloat_mul64To128( sigZ, sigZ );
  56         rem = softfloat_sub128( sigA, 0, term.v64, term.v0 );
  57         while ( UINT64_C( 0x8000000000000000 ) <= rem.v64 ) {
  58             --sigZ;
  59             rem =
  60                 softfloat_add128(
  61                     rem.v64, rem.v0, sigZ>>63, (uint64_t) ( sigZ<<1 ) );
  62         }
  63         sigZ |= ( ( rem.v64 | rem.v0 ) != 0 );
  64     }
  65     return softfloat_roundPackToF64( 0, expZ, sigZ );
  66  invalid:
  67     softfloat_raiseFlags( softfloat_flag_invalid );
  68     uiZ = defaultNaNF64UI;
  69  uiZ:
  70     uZ.ui = uiZ;
  71     return uZ.f;
  72
  73 }
  74