shift.nim

func `shl`*(x: MpUintImpl, y: SomeInteger): MpUintImpl {.inline.}=
  ## Compute the `shift left` operation of x and y
  # Note: inlining this poses codegen/aliasing issue when doing `x = x shl 1`

  # TODO: would it be better to reimplement this using an array of bytes/uint64
  # That opens up to endianness issues.

  const halfSize = size_mpuintimpl(x) div 2
  let defect = halfSize - int(y)

  if y == 0:
    return x
  elif y > size_mpuintimpl(x):
    return
  elif defect > 0:
    result.hi = (x.hi shl y) or (x.lo shr defect)
    result.lo = x.lo shl y
  elif defect < 0:
    result.hi = x.lo shl (-defect)
  else:
    result.hi = x.lo

func `shr`*(x: MpUintImpl, y: SomeInteger): MpUintImpl {.inline.}=
  ## Compute the `shift right` operation of x and y
  const halfSize = size_mpuintimpl(x) div 2
  let defect = halfSize - int(y)

  if y == 0:
    return x
  elif y > size_mpuintimpl(x):
    return
  elif defect > 0:
    result.lo = (x.lo shr y) or (x.hi shr defect)
    result.hi = x.hi shr y
  elif defect < 0:
    result.lo = x.lo shr (-defect)
  else:
    result.lo = x.hi