Add floatop/using_decimal_pkg.go

Author: devlights

examples/basic/floatop/README.md

@@ -6,3 +6,4 @@
 |----|------------|----|
 |order\_of\_computation.go|floatop\_order\_of\_computation|浮動小数点は計算の順序によって結果が変わることのサンプルです|
 |rounding\_error.go|floatop\_rounding\_error|小数点計算において近似値が利用され丸め誤差が出るサンプルです|
+|using\_decimal\_pkg.go|floatop\_using\_decimal\_pkg|小数点計算を github.com/shopspring/decimal パッケージを利用して処理するサンプルです|

examples/basic/floatop/examples.go

@@ -15,4 +15,5 @@ func NewRegister() mapping.Register {
 func (r *register) Regist(m mapping.ExampleMapping) {
 	m["floatop_order_of_computation"] = OrderOfComputation
 	m["floatop_rounding_error"] = RoundingError
+	m["floatop_using_decimal_pkg"] = UsingDecimalPkg
 }

examples/basic/floatop/using_decimal_pkg.go

@@ -0,0 +1,28 @@
+package floatop
+
+import (
+	"github.com/devlights/gomy/output"
+	"github.com/shopspring/decimal"
+)
+
+// UsingDecimalPkg は、小数点計算を github.com/shopspring/decimal パッケージを利用して処理するサンプルです。
+//
+// # REFERENCES
+//   - https://engineering.mercari.com/blog/entry/20201203-basis-point/
+//   - https://github.com/shopspring/decimal
+//
+// # SEE ALSO
+//   - examples/basic/floatop/rounding_error.go
+func UsingDecimalPkg() error {
+	var (
+		v = decimal.RequireFromString("0")
+	)
+
+	for i := 0; i < 1000; i++ {
+		v = v.Add(decimal.RequireFromString(".01"))
+	}
+
+	output.Stdoutl("[result]", v.StringFixed(1))
+
+	return nil
+}

go.mod

@@ -5,6 +5,7 @@ go 1.21
 require (
 	github.com/devlights/gomy v0.6.0
 	github.com/pelletier/go-toml/v2 v2.0.9
+	github.com/shopspring/decimal v1.3.1
 	golang.org/x/crypto v0.11.0
 	golang.org/x/exp v0.0.0-20230713183714-613f0c0eb8a1
 	golang.org/x/sync v0.3.0

go.sum

@@ -7,6 +7,8 @@ github.com/pelletier/go-toml/v2 v2.0.9 h1:uH2qQXheeefCCkuBBSLi7jCiSmj3VRh2+Goq2N
 github.com/pelletier/go-toml/v2 v2.0.9/go.mod h1:tJU2Z3ZkXwnxa4DPO899bsyIoywizdUvyaeZurnPPDc=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/shopspring/decimal v1.3.1 h1:2Usl1nmF/WZucqkFZhnfFYxxxu8LG21F6nPQBE5gKV8=
+github.com/shopspring/decimal v1.3.1/go.mod h1:DKyhrW/HYNuLGql+MJL6WCR6knT2jwCFRcu2hWCYk4o=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
 github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=