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add protomoney Sub fix #72

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merged 2 commits into from
Aug 8, 2024
Merged

add protomoney Sub fix #72

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128b4ae
add protomoney Sub fix
Aug 7, 2024
2eb7821
fix normalising negative unit and positive nanos in protomoney Sub op…
Aug 8, 2024
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16 changes: 14 additions & 2 deletions protomoney/math.go
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Original file line number Diff line number Diff line change
Expand Up @@ -51,11 +51,23 @@ func Add(a, b *money.Money) *money.Money {
// It panics if a and b do not use the same currency.
func Sub(a, b *money.Money) *money.Money {
assertSameCurrency(a, b)
units := a.Units - b.Units
nanos := a.Nanos - b.Nanos

if units > 0 && nanos < 0 {
nanos = nanosPerUnit + nanos
units--
}

if units < 0 && nanos > 0 {
nanos = -(nanosPerUnit - nanos)
units++
}

m := &money.Money{
CurrencyCode: a.CurrencyCode,
Units: a.Units - b.Units,
Nanos: a.Nanos - b.Nanos,
Units: units,
Nanos: nanos,
}

normalizeInPlace(m)
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44 changes: 30 additions & 14 deletions protomoney/math_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -50,20 +50,36 @@ var _ = Describe("func Add()", func() {
})

var _ = Describe("func Sub()", func() {
It("returns a - b", func() {
a := &money.Money{CurrencyCode: "XYZ", Units: 1, Nanos: 230000000}
b := &money.Money{CurrencyCode: "XYZ", Units: 3, Nanos: 450000000}
x := &money.Money{CurrencyCode: "XYZ", Units: -2, Nanos: -220000000}
Expect(Sub(a, b)).To(Equal(x))
})

It("panics if the amounts do not have the same currency", func() {
Expect(func() {
a := &money.Money{CurrencyCode: "XYZ"}
b := &money.Money{CurrencyCode: "ABC"}
Sub(a, b)
}).To(PanicWith("can not operate on amounts in differing currencies (XYZ vs ABC)"))
})
DescribeTable(
"returns a - b",
func(a, b, x *money.Money) {
Expect(Sub(a, b)).To(Equal(x))
},
Entry(
"negative",
&money.Money{CurrencyCode: "XYZ", Units: 1, Nanos: 230000000},
&money.Money{CurrencyCode: "XYZ", Units: 3, Nanos: 450000000},
&money.Money{CurrencyCode: "XYZ", Units: -2, Nanos: -220000000},
),
Entry(
"positive",
&money.Money{CurrencyCode: "XYZ", Units: 3, Nanos: 450000000},
&money.Money{CurrencyCode: "XYZ", Units: 1, Nanos: 230000000},
&money.Money{CurrencyCode: "XYZ", Units: 2, Nanos: 220000000},
),
Entry(
"positive unit and negative nanos are normalized",
&money.Money{CurrencyCode: "XYZ", Units: 40, Nanos: 0},
&money.Money{CurrencyCode: "XYZ", Units: 0, Nanos: 450000000},
&money.Money{CurrencyCode: "XYZ", Units: 39, Nanos: 550000000},
),
Entry(
"negative unit and positive nanos are normalized",
&money.Money{CurrencyCode: "XYZ", Units: 1, Nanos: 200000000},
&money.Money{CurrencyCode: "XYZ", Units: 2, Nanos: 100000000},
&money.Money{CurrencyCode: "XYZ", Units: 0, Nanos: -900000000},
),
)
})

var _ = Describe("func Sum()", func() {
Expand Down