示例#1
0
文件: pslq_test.go 项目: ncw/pslq
func TestSqrt(t *testing.T) {
	tests := []struct {
		prec uint
		in   float64
	}{
		{16, 0},
		{16, 1},
		{16, 4},
		{16, 10000},
		{16, 2},
		{64, 2},
		{256, 2},
		{1024, 1.5},
	}
	for _, test := range tests {
		x := new(big.Float).SetPrec(test.prec)
		x.SetFloat64(test.in)
		var got, got2, diff big.Float
		pslq := New(test.prec)
		pslq.Sqrt(x, &got)
		got2.SetPrec(test.prec).Mul(&got, &got)
		diff.Sub(&got2, x)
		if diff.MinPrec() > 1 {
			t.Errorf("sqrt(%f) prec %d wrong got %.20f square %.20f expecting %f diff %g minprec %d", test.in, test.prec, &got, &got2, x, &diff, diff.MinPrec())
		}
	}
}
示例#2
0
文件: bexport.go 项目: Harvey-OS/go
func (p *exporter) float(x *Mpflt) {
	// extract sign (there is no -0)
	f := &x.Val
	sign := f.Sign()
	if sign == 0 {
		// x == 0
		p.int(0)
		return
	}
	// x != 0

	// extract exponent such that 0.5 <= m < 1.0
	var m big.Float
	exp := f.MantExp(&m)

	// extract mantissa as *big.Int
	// - set exponent large enough so mant satisfies mant.IsInt()
	// - get *big.Int from mant
	m.SetMantExp(&m, int(m.MinPrec()))
	mant, acc := m.Int(nil)
	if acc != big.Exact {
		Fatalf("exporter: internal error")
	}

	p.int(sign)
	p.int(exp)
	p.string(string(mant.Bytes()))
}
示例#3
0
func (p *exporter) float(x constant.Value) {
	if x.Kind() != constant.Float {
		log.Fatalf("gcimporter: unexpected constant %v, want float", x)
	}
	// extract sign (there is no -0)
	sign := constant.Sign(x)
	if sign == 0 {
		// x == 0
		p.int(0)
		return
	}
	// x != 0

	var f big.Float
	if v, exact := constant.Float64Val(x); exact {
		// float64
		f.SetFloat64(v)
	} else if num, denom := constant.Num(x), constant.Denom(x); num.Kind() == constant.Int {
		// TODO(gri): add big.Rat accessor to constant.Value.
		r := valueToRat(num)
		f.SetRat(r.Quo(r, valueToRat(denom)))
	} else {
		// Value too large to represent as a fraction => inaccessible.
		// TODO(gri): add big.Float accessor to constant.Value.
		f.SetFloat64(math.MaxFloat64) // FIXME
	}

	// extract exponent such that 0.5 <= m < 1.0
	var m big.Float
	exp := f.MantExp(&m)

	// extract mantissa as *big.Int
	// - set exponent large enough so mant satisfies mant.IsInt()
	// - get *big.Int from mant
	m.SetMantExp(&m, int(m.MinPrec()))
	mant, acc := m.Int(nil)
	if acc != big.Exact {
		log.Fatalf("gcimporter: internal error")
	}

	p.int(sign)
	p.int(exp)
	p.string(string(mant.Bytes()))
}
示例#4
0
func emitBig(b *big.Float) string {
	digits := bits2digits(b.MinPrec())
	return b.Text('e', int(digits))
}