bit.go

// validRange returns false if 0 is between 1 or starts with 0
// otherwise returns true
func validRange(val byte) bool {
	v := val
	foo := byte(128)
	firstBit := true
	zeroAppears := false
	if v == 0 {
		return false
	}
	for v != 0 {
		if int(v&foo) == 0 {
			if firstBit {
				return false
			}
			zeroAppears = true
		} else {
			if zeroAppears {
				return false
			}
		}
		v = v << 1
		firstBit = false
	}
	return true
}

func Test_validRange(t *testing.T) {
	type args struct {
		val byte
	}
	tests := []struct {
		name string
		args args
		want bool
	}{
		// {args: args{val: 0}, want: false},
		{args: args{val: 1}, want: false},
		{args: args{val: 2}, want: false},
		{args: args{val: 5}, want: false},
		{args: args{val: 127}, want: false},
		{args: args{val: 128}, want: true},
		{args: args{val: 129}, want: false},
		{args: args{val: 192}, want: true},
		{args: args{val: 255}, want: true},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			if got := validRange(tt.args.val); got != tt.want {
				t.Errorf("validRange() = %v, want %v", got, tt.want)
			}
		})
	}
}


// countOne return how many 1 in binary form of a byte
func countOne(val byte) int {
	v := val
	res := 0
	for v != 0 {
		res += int(v & 1)
		v = v >> 1
	}
	return res
}

func Test_countOne(t *testing.T) {
	type args struct {
		val byte
	}
	tests := []struct {
		name string
		args args
		want int
	}{
		{args: args{val: 0}, want: 0},
		{args: args{val: 255}, want: 8},
		{args: args{val: 1}, want: 1},
		{args: args{val: 2}, want: 1},
		{args: args{val: 3}, want: 2},
		{args: args{val: 4}, want: 1},
		{args: args{val: 5}, want: 2},
		{args: args{val: 6}, want: 2},
		{args: args{val: 7}, want: 3},
		{args: args{val: 8}, want: 1},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			if got := countOne(tt.args.val); got != tt.want {
				t.Errorf("countOne() = %v, want %v", got, tt.want)
			}
		})
	}
}