Rob Pike's integer multiplication overflow tests from golang-nuts mailing list

gistfile1.go

func mulOverflows(a, b uint64) bool {
  if a <= 1 || b <= 1 {
    return false
  }
  c := a * b
  return c/b != a
}

const mostNegative = -(mostPositive + 1)
const mostPositive = 1<<63 - 1

func signedMulOverflows(a, b int64) bool {
  if a == 0 || b == 0 || a == 1 || b == 1 {
    return false
  }
  if a == mostNegative || b == mostNegative {
    return true
  }
  c := a * b
  return c/b != a
}