nim-stint/tests/test_muldiv.nim

# Mpint
# Copyright 2018 Status Research & Development GmbH
# Licensed under either of
#
#  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
#  * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
#
# at your option. This file may not be copied, modified, or distributed except according to those terms.

import ../src/mpint, unittest

suite "Testing multiplication implementation":
  test "Multiplication with result fitting in low half":

    let a = 10000.initMpUint(64)
    let b = 10000.initMpUint(64)

    check: cast[uint64](a*b) == 100_000_000'u64 # need 27-bits

  test "Multiplication with result overflowing low half":

    let a = 1_000_000.initMpUint(64)
    let b = 1_000_000.initMpUint(64)

    check: cast[uint64](a*b) == 1_000_000_000_000'u64 # need 40 bits

  test "Full overflow is handled like native unsigned types":

    let a = 1_000_000_000.initMpUint(64)
    let b = 1_000_000_000.initMpUint(64)
    let c = 1_000.initMpUint(64)

    check: cast[uint64](a*b*c) == 1_000_000_000_000_000_000_000'u64 # need 70-bits


suite "Testing division and modulo implementation":
  test "Divmod(100, 13) returns the correct result":

    let a = 100.initMpUint(64)
    let b = 13.initMpUint(64)
    let qr = divmod(a, b)

    check: cast[uint64](qr.quot) == 7'u64
    check: cast[uint64](qr.rem)  == 9'u64

  test "Divmod(2^64, 3) returns the correct result":
    let a = 1.initMpUint(128) shl 64
    let b = 3.initMpUint(128)

    let qr = divmod(a, b)

    let q = cast[MpUintImpl[uint64]](qr.quot)
    let r = cast[MpUintImpl[uint64]](qr.rem)

    check: q.lo == 6148914691236517205'u64
    check: q.hi == 0'u64
    check: r.lo == 1'u64
    check: r.hi == 0'u64