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basic_operators.go
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157 lines (141 loc) · 3.96 KB
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package decimal
import "math/big"
// Add returns d + d2
func (d BigDecimal) Add(d2 BigDecimal) BigDecimal {
rd, rd2 := rescalePair(d, d2)
d3Value := new(big.Int).Add(rd.value, rd2.value)
nn, nd := addFraction(rd.numerator, rd.denominator, rd2.numerator, rd2.denominator)
newBD := BigDecimal{
value: d3Value,
scale: rd.scale,
numerator: nn,
denominator: nd,
}
newBD.optimize()
return newBD
}
// Sub returns d - d2
func (d BigDecimal) Sub(d2 BigDecimal) BigDecimal {
rd, rd2 := rescalePair(d, d2)
d3Value := new(big.Int).Sub(rd.value, rd2.value)
nn, nd := subFraction(rd.numerator, rd.denominator, rd2.numerator, rd2.denominator)
if nn < 0 {
d3Value.Sub(d3Value, oneInt)
nn += int64(nd)
}
newBD := BigDecimal{
value: d3Value,
scale: rd.scale,
numerator: uint64(nn),
denominator: nd,
}
newBD.optimize()
return newBD
}
// Mul returns d * d2
func (d BigDecimal) Mul(d2 BigDecimal) BigDecimal {
var (
nn int64
nd uint64
)
d3Value := new(big.Int).Mul(d.value, d2.value)
if d.denominator == 0 && d2.denominator != 0 {
nn = d.value.Int64() * int64(d2.numerator)
nd = d2.denominator
}
if d.denominator != 0 && d2.denominator == 0 {
nn = d2.value.Int64() * int64(d.numerator)
nd = d.denominator
}
if d.denominator != 0 && d2.denominator != 0 {
nn = d.value.Int64() * int64(d.denominator) * int64(d2.numerator)
nn += d2.value.Int64() * int64(d2.denominator) * int64(d.numerator)
nn += int64(d.numerator) * int64(d2.numerator)
nd = d.denominator * d.denominator
}
if nn < 0 {
d3Value.Sub(d3Value, new(big.Int).SetInt64(nn/int64(nd)))
nn %= int64(nd)
if nn < 0 {
d3Value.Sub(d3Value, oneInt)
nn += int64(nd)
}
}
newBD := BigDecimal{
value: d3Value,
scale: d.scale + d2.scale,
numerator: uint64(nn),
denominator: nd,
}
newBD.optimize()
return newBD
}
// Div returns d / d2
// The return value will be recurring decimal if can
func (d BigDecimal) Div(d2 BigDecimal) BigDecimal {
if d2.Cmp(Zero) == 0 {
panic("divise by zero")
}
// We have:
// D := (v1 + n1/d1) * 10^(-s1)
// D2 := (v2 + n2/d2) * 10^(-s2)
// So:
// D v1 + n1/d1
// ---- = ---------------- * 10^-(s1-s2) (1)
// D2 v2 + n2/d2
//
// D (v1 * d1 + n1) * d2
// <=> ---- = ----------------------- * 10^-(s1-s2) (2)
// D2 (v2 * d2 + n2) * d1
var (
// Set dn = v1, dd = v2
dn = new(big.Int).Set(d.value) // Decimal numerator
dd = new(big.Int).Set(d2.value) // Decimal denominator
// Set dd1 = d1, dd2 = d2
dd1 = new(big.Int).SetUint64(d.denominator) // Decimal of d1
dd2 = new(big.Int).SetUint64(d2.denominator) // Decimal of d2
)
// If d1 != 0, we can calculate dn = v1 * d1 + n1 (3)
if d.denominator != 0 {
dn = dn.Mul(dn, dd1)
dn = dn.Add(dn, new(big.Int).SetUint64(d.numerator))
}
// If d2 != 0, we can calculate dd = v2 * d2 + n2 (4)
if d2.denominator != 0 {
dd = dd.Mul(dd, dd2)
dd = dd.Add(dd, new(big.Int).SetUint64(d2.numerator))
}
if d.denominator != 0 && d2.denominator != 0 {
// This case d1 and d2 != 0 both
// We calculate dn and dd base on the (2) calculation above
dn = dn.Mul(dn, dd2)
dd = dd.Mul(dd, dd1)
} else if d2.denominator != 0 {
// In case, d2 != 0 and d1 == 0
// D v1 * d2
// ---- = -------------- (5)
// D2 v2 * d2 + n2
// => So we keep the dd as (4) above
dn = dn.Mul(dn, dd2)
} else if d.denominator != 0 {
// In case, d1 != 0 and d2 == 0
// D v1 * d1 + n1
// ---- = -------------- (6)
// D2 v2 * d1
// => So we keep the dn as (3) above
dd = dd.Mul(dd, dd1)
}
// q and r are quotient and remainder
// helps to calculate the D/D2 based on (2) or (5) or (6)
// q will be saved as value
// r will be saved as numerator of result
q, r := new(big.Int).QuoRem(dn, dd, new(big.Int))
newBD := BigDecimal{
value: q,
scale: d.scale - d2.scale, // based on (2)
numerator: r.Uint64(),
denominator: dd.Uint64(),
}
newBD.optimize()
return newBD
}