Add find number of digits example

Author: devlights

examples/singleapp/find_number_of_digits/README.md

@@ -0,0 +1,30 @@
+# これは何？
+
+特定の数値の桁数を求める方法として
+
+- 一度文字列化し、その文字数を数える
+- Log10の値をFloor+1する
+
+という２つの方法で試した場合の速度差を見るサンプルです。
+
+Gitpod上で実行すると、例えば以下のような結果が得られます。
+
+```sh
+$ task 
+[ToString] 9    [Log10] 9
+----------------------------------------
+=== RUN   TestFn
+--- PASS: TestFn (0.00s)
+PASS
+ok      command-line-arguments  0.002s
+----------------------------------------
+goos: linux
+goarch: amd64
+cpu: AMD EPYC 7B13
+BenchmarkUseToString-16         34382973                35.82 ns/op
+BenchmarkUseLog10-16            96657720                12.26 ns/op
+PASS
+ok      command-line-arguments  2.473s
+```
+
+後者の方が倍以上速いことが分かります。

examples/singleapp/find_number_of_digits/Taskfile.yml

@@ -0,0 +1,13 @@
+# https://taskfile.dev
+
+version: '3'
+
+tasks:
+  default:
+    cmds:
+      - go run main.go
+      - echo '----------------------------------------'
+      - go test -v lib/*
+      - echo '----------------------------------------'      
+      - go test -bench . lib/*
+    silent: true

examples/singleapp/find_number_of_digits/lib/fn.go

@@ -0,0 +1,18 @@
+package lib
+
+import (
+	"math"
+	"strconv"
+)
+
+type (
+	NumberOfDigits int
+)
+
+func UseToString(v int) NumberOfDigits {
+	return NumberOfDigits(len(strconv.Itoa(v)))
+}
+
+func UseLog10(v int) NumberOfDigits {
+	return NumberOfDigits(int(math.Floor(math.Log10(float64(v)))) + 1)
+}

examples/singleapp/find_number_of_digits/lib/fn_test.go

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+package lib
+
+import "testing"
+
+func TestFn(t *testing.T) {
+	testcases := []struct {
+		name string
+		in   int
+		out  NumberOfDigits
+	}{
+		{"1", 1, NumberOfDigits(1)},
+		{"10", 10, NumberOfDigits(2)},
+		{"100", 100, NumberOfDigits(3)},
+		{"9999", 9999, NumberOfDigits(4)},
+		{"123456789", 123456789, NumberOfDigits(9)},
+		{"1234567890", 1234567890, NumberOfDigits(10)},
+	}
+
+	for _, tc := range testcases {
+		tc := tc
+
+		if v := UseToString(tc.in); v != tc.out {
+			t.Errorf("%s-UseToString: [want] %v\t[got] %v", tc.name, tc.out, v)
+		}
+
+		if v := UseLog10(tc.in); v != tc.out {
+			t.Errorf("%s-UseLog10: [want] %v\t[got] %v", tc.name, tc.out, v)
+		}
+	}
+}
+
+func BenchmarkUseToString(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		UseToString(123456789)
+	}
+}
+
+func BenchmarkUseLog10(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		UseLog10(123456789)
+	}
+}

examples/singleapp/find_number_of_digits/main.go

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+package main
+
+import (
+	"fmt"
+
+	"github.com/devlights/try-golang/examples/singleapp/find_number_of_digits/lib"
+)
+
+func main() {
+	if err := run(); err != nil {
+		panic(err)
+	}
+}
+
+func run() error {
+	v := 123456789
+	fmt.Printf("[ToString] %v\t[Log10] %v\n", lib.UseToString(v), lib.UseLog10(v))
+
+	return nil
+}