package fixed

import "testing"

func TestFromIntAndBack(t *testing.T) {
	if got := FromInt(7).Int(); got != 7 {
		t.Fatalf("FromInt(7).Int() = %d, want 7", got)
	}
}

func TestMulIsExact(t *testing.T) {
	half := One / 2
	if got := half.Mul(half); got != One/4 {
		t.Fatalf("0.5*0.5 = %d, want %d", got, One/4)
	}
}

func TestMulDoesNotOverflowAtScale(t *testing.T) {
	// A naive (a*b)>>32 overflows well below this. The 128-bit intermediate
	// must handle it exactly.
	a := FromInt(100000)
	if got := a.Mul(FromInt(2)); got != FromInt(200000) {
		t.Fatalf("100000*2 = %v, want 200000", got)
	}
}

func TestDivIsExact(t *testing.T) {
	if got := FromInt(1).Div(FromInt(4)); got != One/4 {
		t.Fatalf("1/4 = %d, want %d", got, One/4)
	}
}

func TestNegativeMulAndDiv(t *testing.T) {
	if got := FromInt(-3).Mul(FromInt(4)); got != FromInt(-12) {
		t.Fatalf("-3*4 = %v, want -12", got)
	}
	if got := FromInt(-12).Div(FromInt(4)); got != FromInt(-3) {
		t.Fatalf("-12/4 = %v, want -3", got)
	}
}

func TestSqrt(t *testing.T) {
	for _, n := range []int64{0, 1, 4, 9, 16, 100, 10000} {
		want := FromInt(isqrt(n))
		got := Sqrt(FromInt(n))
		if got != want {
			t.Fatalf("Sqrt(%d) = %v, want %v", n, got, want)
		}
	}
}

func isqrt(n int64) int64 {
	var r int64
	for r*r <= n {
		r++
	}
	return r - 1
}

func TestString(t *testing.T) {
	if got := (One + One/2).String(); got != "1.500000" {
		t.Fatalf("1.5.String() = %q", got)
	}
	if got := FromInt(-2).String(); got != "-2.000000" {
		t.Fatalf("-2.String() = %q", got)
	}
}
