align.go

package main

import (
	"fmt"
)

func main() {
	fmt.Println("Sz", "Pg", "Bn", "Pad")
	pageSize := 1 << 5
	for _, off := range []int{10, 15, 16, 31, 33} {
		bound := alignBound(off, pageSize)
		fmt.Println(off, pageSize, bound, bound-off)
	}
}

func alignBound(off, page int) int {
	return (off + page - 1) & ^(page - 1)
}

Live code - https://play.golang.org/p/I51R7D5Dnd
Output:

Sz Pg Bn Pad
10 32 32 22
15 32 32 17
16 32 32 16
31 32 32 1
33 32 64 31