func arithDivide(a, b *big.Float) (*big.Float, error) {
i, acc := b.Int64()
if acc == big.Exact && i == 0 {
return nil, fmt.Errorf("divide: by zero")
}
return new(big.Float).Quo(a, b), nil
}
func (bed BinaryIntEncoderDecoder) Encode(w io.Writer, n *big.Float) error {
if n.IsInt() {
x, _ := n.Int64()
// TODO - if accuracy is not Exact, then use the other path
if err := binary.Write(w, binary.BigEndian, int8(0)); err != nil {
return err
}
return binary.Write(w, binary.BigEndian, x)
} else {
if err := binary.Write(w, binary.BigEndian, int8(1)); err != nil {
return err
}
exponent := n.MantExp(bed.tmp)
f, _ := bed.tmp.Float64()
if err := binary.Write(w, binary.BigEndian, f); err != nil {
return err
}
return binary.Write(w, binary.BigEndian, int32(exponent))
}
}
// Pow returns a big.Float representation of z**w. Precision is the same as the one
// of the first argument. The function panics when z is negative.
func Pow(z *big.Float, w *big.Float) *big.Float {
if z.Sign() < 0 {
panic("Pow: negative base")
}
// Pow(z, 0) = 1.0
if w.Sign() == 0 {
return big.NewFloat(1).SetPrec(z.Prec())
}
// Pow(z, 1) = z
// Pow(+Inf, n) = +Inf
if w.Cmp(big.NewFloat(1)) == 0 || z.IsInf() {
return new(big.Float).Copy(z)
}
// Pow(z, -w) = 1 / Pow(z, w)
if w.Sign() < 0 {
x := new(big.Float)
zExt := new(big.Float).Copy(z).SetPrec(z.Prec() + 64)
wNeg := new(big.Float).Neg(w)
return x.Quo(big.NewFloat(1), Pow(zExt, wNeg)).SetPrec(z.Prec())
}
// w integer fast path
if w.IsInt() {
wi, _ := w.Int64()
return powInt(z, int(wi))
}
// compute w**z as exp(z log(w))
x := new(big.Float).SetPrec(z.Prec() + 64)
logZ := Log(new(big.Float).Copy(z).SetPrec(z.Prec() + 64))
x.Mul(w, logZ)
x = Exp(x)
return x.SetPrec(z.Prec())
}
func (bed BinaryVarintEncoderDecoder) Encode(w io.Writer, n *big.Float) error {
if n.IsInt() {
x, _ := n.Int64()
// TODO - if accuracy is not Exact, then use the other path
buf := make([]byte, binary.MaxVarintLen64)
nBytes := binary.PutVarint(buf, x)
if _, err := w.Write([]byte{byte(0)}); err != nil {
return err
}
_, err := w.Write(buf[0:nBytes])
return err
} else {
if err := binary.Write(w, binary.BigEndian, int8(1)); err != nil {
return err
}
exponent := n.MantExp(bed.tmp)
f, _ := bed.tmp.Float64()
if err := binary.Write(w, binary.BigEndian, f); err != nil {
return err
}
return binary.Write(w, binary.BigEndian, int32(exponent))
}
}
