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feat: RoundHalfTowardZero()

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This commit is contained in:
yzy613 2024-07-18 21:11:12 +08:00
parent 840ef45ca8
commit 54e62db847
2 changed files with 63 additions and 3 deletions
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37
decimal.go
View file

@ -1513,7 +1513,7 @@ func (d Decimal) StringFixedCash(interval uint8) string {
return rounded.string(false)
}
// Round rounds the decimal to places decimal places.
// Round rounds the decimal to places decimal places (half away from zero).
// If places < 0, it will round the integer part to the nearest 10^(-places).
//
// Example:
@ -1544,6 +1544,37 @@ func (d Decimal) Round(places int32) Decimal {
return ret
}
// RoundHalfTowardZero rounds the decimal to places decimal places (half toward zero).
// If places < 0, it will round the integer part to the nearest 10^(-places).
//
// Example:
//
// NewFromFloat(5.45).RoundHalfTowardZero(1).String() // output: "5.4"
// NewFromFloat(545).RoundHalfTowardZero(-1).String() // output: "540"
func (d Decimal) RoundHalfTowardZero(places int32) Decimal {
if d.exp == -places {
return d
}
// truncate to places + 1
ret := d.rescale(-places - 1)
// add sign(d) * 0.4
if ret.value.Sign() < 0 {
ret.value.Sub(ret.value, fourInt)
} else {
ret.value.Add(ret.value, fourInt)
}
// floor for positive numbers, ceil for negative numbers
_, m := ret.value.DivMod(ret.value, tenInt, new(big.Int))
ret.exp++
if ret.value.Sign() < 0 && m.Cmp(zeroInt) != 0 {
ret.value.Add(ret.value, oneInt)
}
return ret
}
// RoundHalfUp rounds the decimal half towards +infinity.
//
// Example:
@ -1560,7 +1591,7 @@ func (d Decimal) RoundHalfUp(places int32) Decimal {
// truncate to places + 1
ret := d.rescale(-places - 1)
// add sign(d) * 0.5
// add sign(d) * 0.5 if sign(d) >= 0 else sign(d) * 0.4
if ret.value.Sign() < 0 {
ret.value.Sub(ret.value, fourInt)
} else {
@ -1593,7 +1624,7 @@ func (d Decimal) RoundHalfDown(places int32) Decimal {
// truncate to places + 1
ret := d.rescale(-places - 1)
// add sign(d) * 0.5
// add sign(d) * 0.5 if sign(d) < 0 else sign(d) * 0.4
if ret.value.Sign() < 0 {
ret.value.Sub(ret.value, fiveInt)
} else {

29
decimal_test.go
View file

@ -3753,3 +3753,32 @@ func TestDecimal_RoundHalfDown(t *testing.T) {
})
}
}
func TestDecimal_RoundHalfTowardZero(t *testing.T) {
tests := []struct {
name string
d Decimal
places int32
want Decimal
}{
{
name: "5.45",
d: NewFromFloat(5.45),
places: 1,
want: NewFromFloat(5.4),
},
{
name: "545",
d: NewFromInt(545),
places: -1,
want: NewFromInt(540),
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
if got := tt.d.RoundHalfTowardZero(tt.places); !got.Equal(tt.want) {
t.Errorf("RoundHalfDown() = %v, want %v", got, tt.want)
}
})
}
}