float problem

test.go

package main

import "fmt"

func main() {
	testFloat((1+0.8)/2, float64(16))
	testFloat((1+0.8)/2, float64(15))
}

func testFloat(x, y float64) {
	z := x + y
	fmt.Println()
	fmt.Println(`x =`, x)
	fmt.Println(`y =`, y)
	fmt.Println(`z =`, z)
	fmt.Println(`z - y =`, z-y)
	fmt.Println(`(z-y) >  x: `, (z-y) > x)
	fmt.Println(`(z-y) == x: `, (z-y) == x)
	fmt.Println(`(z-y) <  x: `, (z-y) < x)
}

/*

# go version
go version go1.10.3 linux/amd64

# go run test.go

x = 0.9
y = 16
z = 16.9
z - y = 0.8999999999999986
(z-y) >  x:  false
(z-y) == x:  false
(z-y) <  x:  true

x = 0.9
y = 15
z = 15.9
z - y = 0.9000000000000004
(z-y) >  x:  true
(z-y) == x:  false
(z-y) <  x:  false

*/