align.nim

proc allocAligned(size, alignment: int): tuple[base, start: pointer] =
  assert((alignment and (alignment - 1)) == 0) # Power of 2?
  var address = alloc0(size+alignment)
  if (cast[int](address) and (alignment - 1)) == 0:
    (address, address)
  else:
    let offset = alignment - (cast[int](address) and (alignment - 1))
    (address, cast[pointer](cast[int](address) + offset))

when isMainModule:
  echo repr(allocAligned(128, 4))
  echo repr(allocAligned(1024, 256))