bitfield.nim

## Provides utility methods to make working with bit manipulations
## easier and less error prone
const
  validBitfieldType = ["int", "int8", "int16", "int32", "int64", "uint",
                       "uint8", "uint16", "uint32", "uint64", "bool"]
macro bitfield(values: varargs[stmt]): stmt =
  ## Creates a bitfield with the given fields
  # Validate and initial parameter processing
  if values.len %% 3 != 0:
    error("Each field requires three values")
  var fields = newSeq[tuple[typ, name: string, size: int]](values.len div 3)
  var numSize = 0
  for i in 0..(values.len div 3 - 1):
    let typ  = values[i*3]
    let name = values[i*3 + 1]
    let size = values[i*3 + 2]
    if typ.kind != nnkSym or not validBitfieldType.contains($typ):
      error("Type `" & $typ & "` is either not a type or an invalid one")
    if not (name.kind in {nnkStrLit, nnkRStrLit, nnkTripleStrLit}) or
       (not validIdentifier(name.strVal) and name.strVal != ""):
      error("Name `" & name.strVal & "` either not a literal string or an " &
            "invalid identifier")
    if not (size.kind in {nnkIntLit .. nnkUInt64Lit}):
      error("The size of `" &  name.strVal & "` is not an integer")
    fields[i] = (typ: $typ, name: name.strVal, size: size.intVal.int)
    numSize += size.intVal.int
  if not (numSize in {8, 16, 32, 64}):
    error($numSize & "can only be one of 8, 16, 32, or 64. " &
         "Adding padding may help")