Function floatx80_sqrt

src/softfloat/softfloat.cpp:3090–3152

*----------------------------------------------------------------------------*/

floatx80 floatx80_sqrt(floatx80 a, float_status *status)
{
    flag aSign;
    int32_t aExp, zExp;
    uint64_t aSig0, aSig1, zSig0, zSig1, doubleZSig0;
    uint64_t rem0, rem1, rem2, rem3, term0, term1, term2, term3;

    if (floatx80_invalid_encoding(a)) {
        float_raise(float_flag_invalid, status);
        return floatx80_default_nan(status);
    }
    aSig0 = extractFloatx80Frac( a );
    aExp = extractFloatx80Exp( a );
    aSign = extractFloatx80Sign( a );
    if ( aExp == 0x7FFF ) {
        if ((uint64_t)(aSig0 << 1))
            return propagateFloatx80NaNOneArg(a, status);
		if (!aSign) return inf_clear_intbit(status) ? packFloatx80(aSign, aExp, 0) : a;
        goto invalid;
    }
    if ( aSign ) {
        if ( ( aExp | aSig0 ) == 0 ) return a;
 invalid:
        float_raise(float_flag_invalid, status);
        return floatx80_default_nan(status);
    }
    if ( aExp == 0 ) {
        if ( aSig0 == 0 ) return packFloatx80( 0, 0, 0 );
        normalizeFloatx80Subnormal( aSig0, &aExp, &aSig0 );
    }
    zExp = ( ( aExp - 0x3FFF )>>1 ) + 0x3FFF;
    zSig0 = estimateSqrt32( aExp, aSig0>>32 );
    shift128Right( aSig0, 0, 2 + ( aExp & 1 ), &aSig0, &aSig1 );
    zSig0 = estimateDiv128To64( aSig0, aSig1, zSig0<<32 ) + ( zSig0<<30 );
    doubleZSig0 = zSig0<<1;
    mul64To128( zSig0, zSig0, &term0, &term1 );
    sub128( aSig0, aSig1, term0, term1, &rem0, &rem1 );
    while ( (int64_t) rem0 < 0 ) {
        --zSig0;
        doubleZSig0 -= 2;
        add128( rem0, rem1, zSig0>>63, doubleZSig0 | 1, &rem0, &rem1 );
    }
    zSig1 = estimateDiv128To64( rem1, 0, doubleZSig0 );
    if ( ( zSig1 & LIT64( 0x3FFFFFFFFFFFFFFF ) ) <= 5 ) {
        if ( zSig1 == 0 ) zSig1 = 1;
        mul64To128( doubleZSig0, zSig1, &term1, &term2 );
        sub128( rem1, 0, term1, term2, &rem1, &rem2 );
        mul64To128( zSig1, zSig1, &term2, &term3 );
        sub192( rem1, rem2, 0, 0, term2, term3, &rem1, &rem2, &rem3 );
        while ( (int64_t) rem1 < 0 ) {
            --zSig1;
            shortShift128Left( 0, zSig1, 1, &term2, &term3 );
            term3 |= 1;
            term2 |= doubleZSig0;
            add192( rem1, rem2, rem3, 0, term2, term3, &rem1, &rem2, &rem3 );
        }
        zSig1 |= ( ( rem1 | rem2 | rem3 ) != 0 );
    }