benchmarks

$ go test -bench=.
testing: warning: no tests to run
PASS
BenchmarkIntersectWithZR        50000000                29.5 ns/op
BenchmarkIntersectWithoutZR     50000000                35.5 ns/op
ok      stani.be/temp/polyclip/zr       3.318s

35.5/29.5 = 1,20 

zr.go

package zr

type Point struct {
	X, Y float64
}

type Rectangle struct {
	Min, Max Point
}

var ZR Rectangle

func (r Rectangle) Intersect1(s Rectangle) Rectangle {
	if r.Min.X < s.Min.X {
		r.Min.X = s.Min.X
	}
	if r.Min.Y < s.Min.Y {
		r.Min.Y = s.Min.Y
	}
	if r.Max.X > s.Max.X {
		r.Max.X = s.Max.X
	}
	if r.Max.Y > s.Max.Y {
		r.Max.Y = s.Max.Y
	}
	if r.Min.X > r.Max.X || r.Min.Y > r.Max.Y {
		return ZR
	}
	return r
}

func (r Rectangle) Intersect2(s Rectangle) Rectangle {
	if r.Min.X < s.Min.X {
		r.Min.X = s.Min.X
	}
	if r.Min.Y < s.Min.Y {
		r.Min.Y = s.Min.Y
	}
	if r.Max.X > s.Max.X {
		r.Max.X = s.Max.X
	}
	if r.Max.Y > s.Max.Y {
		r.Max.Y = s.Max.Y
	}
	if r.Min.X > r.Max.X || r.Min.Y > r.Max.Y {
		return Rectangle{}
	}
	return r
}

zr_test.go

package zr

import "testing"

var result1, result2 bool

func BenchmarkIntersectWithZR(b *testing.B) {
	r := Rectangle{Point{0, 0}, Point{1, 1}}
	s := Rectangle{Point{2, 2}, Point{3, 3}}
	for n := 0; n < b.N; n++ {
		i := r.Intersect1(s)
		result1 = i == ZR
	}
}

func BenchmarkIntersectWithoutZR(b *testing.B) {
	r := Rectangle{Point{0, 0}, Point{1, 1}}
	s := Rectangle{Point{2, 2}, Point{3, 3}}
	for n := 0; n < b.N; n++ {
		i := r.Intersect2(s)
		result2 = i == Rectangle{}
	}
}