// continuedFraction calculates and returns the best rational approximation of the given real number.
func continuedFraction(price string) (xdrPrice xdr.Price, err error) {
number := &big.Rat{}
maxInt32 := &big.Rat{}
zero := &big.Rat{}
one := &big.Rat{}
_, ok := number.SetString(price)
if !ok {
return xdrPrice, fmt.Errorf("cannot parse price: %s", price)
}
maxInt32.SetInt64(int64(math.MaxInt32))
zero.SetInt64(int64(0))
one.SetInt64(int64(1))
fractions := [][2]*big.Rat{
{zero, one},
{one, zero},
}
i := 2
for {
if number.Cmp(maxInt32) == 1 {
break
}
f := &big.Rat{}
h := &big.Rat{}
k := &big.Rat{}
a := floor(number)
f.Sub(number, a)
h.Mul(a, fractions[i-1][0])
h.Add(h, fractions[i-2][0])
k.Mul(a, fractions[i-1][1])
k.Add(k, fractions[i-2][1])
if h.Cmp(maxInt32) == 1 || k.Cmp(maxInt32) == 1 {
break
}
fractions = append(fractions, [2]*big.Rat{h, k})
if f.Cmp(zero) == 0 {
break
}
number.Quo(one, f)
i++
}
n, d := fractions[len(fractions)-1][0], fractions[len(fractions)-1][1]
if n.Cmp(zero) == 0 || d.Cmp(zero) == 0 {
return xdrPrice, errors.New("Couldn't find approximation")
}
return xdr.Price{
N: xdr.Int32(n.Num().Int64()),
D: xdr.Int32(d.Num().Int64()),
}, nil
}
It("sets values properly", func() {
builder := CreateOffer(rate, "20")
Expect(builder.MO.Amount).To(Equal(xdr.Int64(200000000)))
Expect(builder.MO.Selling.Type).To(Equal(xdr.AssetTypeAssetTypeCreditAlphanum4))
Expect(builder.MO.Selling.AlphaNum4.AssetCode).To(Equal([4]byte{'E', 'U', 'R', 0}))
aid, _ := stellarbase.AddressToAccountId(rate.Selling.Issuer)
Expect(builder.MO.Selling.AlphaNum4.Issuer.MustEd25519()).To(Equal(aid.MustEd25519()))
Expect(builder.MO.Selling.AlphaNum12).To(BeNil())
Expect(builder.MO.Buying.Type).To(Equal(xdr.AssetTypeAssetTypeNative))
Expect(builder.MO.Buying.AlphaNum4).To(BeNil())
Expect(builder.MO.Buying.AlphaNum12).To(BeNil())
Expect(builder.MO.Price.N).To(Equal(xdr.Int32(8253)))
Expect(builder.MO.Price.D).To(Equal(xdr.Int32(200)))
Expect(builder.MO.OfferId).To(Equal(xdr.Uint64(0)))
})
})
})
Describe("UpdateOffer", func() {
Context("updates the offer properly", func() {
It("sets values properly", func() {
builder := UpdateOffer(rate, "100", 5)
Expect(builder.MO.Amount).To(Equal(xdr.Int64(1000000000)))
Expect(builder.MO.Selling.Type).To(Equal(xdr.AssetTypeAssetTypeCreditAlphanum4))