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optimize NewFromString a bit (#198)
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* optimize NewFromString a bit

* add benchmark for large number

Co-authored-by: Nicholas Nordeen <[email protected]>
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nknordeen and Nicholas Nordeen authored Jan 10, 2021
1 parent 8bd41ac commit 0cada0b
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Showing 2 changed files with 74 additions and 11 deletions.
44 changes: 33 additions & 11 deletions decimal.go
Original file line number Diff line number Diff line change
Expand Up @@ -147,23 +147,45 @@ func NewFromString(value string) (Decimal, error) {
exp = expInt
}

parts := strings.Split(value, ".")
if len(parts) == 1 {
pIndex := -1
vLen := len(value)
for i := 0; i < vLen; i++ {
if value[i] == '.' {
if pIndex > -1 {
return Decimal{}, fmt.Errorf("can't convert %s to decimal: too many .s", value)
}
pIndex = i
}
}

if pIndex == -1 {
// There is no decimal point, we can just parse the original string as
// an int
intString = value
} else if len(parts) == 2 {
intString = parts[0] + parts[1]
expInt := -len(parts[1])
exp += int64(expInt)
} else {
return Decimal{}, fmt.Errorf("can't convert %s to decimal: too many .s", value)
if pIndex+1 < vLen {
intString = value[:pIndex] + value[pIndex+1:]
} else {
intString = value[:pIndex]
}
expInt := -len(value[pIndex+1:])
exp += int64(expInt)
}

dValue := new(big.Int)
_, ok := dValue.SetString(intString, 10)
if !ok {
return Decimal{}, fmt.Errorf("can't convert %s to decimal", value)
var dValue *big.Int
// strconv.ParseInt is faster than new(big.Int).SetString so this is just a shortcut for strings we know won't overflow
if len(intString) <= 18 {
parsed64, err := strconv.ParseInt(intString, 10, 64)
if err != nil {
return Decimal{}, fmt.Errorf("can't convert %s to decimal", value)
}
dValue = big.NewInt(parsed64)
} else {
dValue = new(big.Int)
_, ok := dValue.SetString(intString, 10)
if !ok {
return Decimal{}, fmt.Errorf("can't convert %s to decimal", value)
}
}

if exp < math.MinInt32 || exp > math.MaxInt32 {
Expand Down
41 changes: 41 additions & 0 deletions decimal_bench_test.go
Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
package decimal

import (
"fmt"
"math"
"math/rand"
"sort"
Expand Down Expand Up @@ -183,3 +184,43 @@ func BenchmarkDecimal_IsInteger(b *testing.B) {
d.IsInteger()
}
}

func BenchmarkDecimal_NewFromString(b *testing.B) {
count := 72
prices := make([]string, 0, count)
for i := 1; i <= count; i++ {
prices = append(prices, fmt.Sprintf("%d.%d", i*100, i))
}

b.ReportAllocs()
b.ResetTimer()
for i := 0; i < b.N; i++ {
for _, p := range prices {
d, err := NewFromString(p)
if err != nil {
b.Log(d)
b.Error(err)
}
}
}
}

func BenchmarkDecimal_NewFromString_large_number(b *testing.B) {
count := 72
prices := make([]string, 0, count)
for i := 1; i <= count; i++ {
prices = append(prices, "9323372036854775807.9223372036854775807")
}

b.ReportAllocs()
b.ResetTimer()
for i := 0; i < b.N; i++ {
for _, p := range prices {
d, err := NewFromString(p)
if err != nil {
b.Log(d)
b.Error(err)
}
}
}
}

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