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use essential_types::{convert::bool_from_word, Word};
use crate::{
error::{OpResult, RepeatError, RepeatResult, StackError},
Stack,
};
#[cfg(test)]
mod tests;
#[derive(Clone, Debug, Default, PartialEq)]
/// A stack of repeat counters.
pub struct Repeat {
stack: Vec<Slot>,
}
#[derive(Clone, Debug, PartialEq)]
struct Slot {
pub counter: Word,
pub limit: Direction,
pub repeat_index: usize,
}
#[derive(Clone, Debug, PartialEq)]
enum Direction {
Up(Word),
Down,
}
/// `Stack::Repeat` implementation.
pub(crate) fn repeat(pc: usize, stack: &mut Stack, repeat: &mut Repeat) -> OpResult<()> {
let [num_repeats, count_up] = stack.pop2()?;
let count_up = bool_from_word(count_up).ok_or(RepeatError::InvalidCountDirection)?;
let pc = pc.checked_add(1).ok_or(StackError::IndexOutOfBounds)?;
if count_up {
repeat.repeat_to(pc, num_repeats)?;
} else {
repeat.repeat_from(pc, num_repeats)?;
}
Ok(())
}
impl Repeat {
/// Create a new repeat stack.
pub fn new() -> Self {
Self::default()
}
/// Add a new repeat location and counter to the stack.
/// Counts down to 0.
pub fn repeat_from(&mut self, location: usize, amount: Word) -> RepeatResult<()> {
if self.stack.len() >= super::Stack::SIZE_LIMIT {
return Err(RepeatError::Overflow);
}
self.stack.push(Slot {
counter: amount,
limit: Direction::Down,
repeat_index: location,
});
Ok(())
}
/// Add a new repeat location and counter to the stack.
/// Counts up from 0 to limit - 1.
pub fn repeat_to(&mut self, location: usize, limit: Word) -> RepeatResult<()> {
if self.stack.len() >= super::Stack::SIZE_LIMIT {
return Err(RepeatError::Overflow);
}
self.stack.push(Slot {
counter: 0,
limit: Direction::Up(limit),
repeat_index: location,
});
Ok(())
}
/// Get the current repeat counter.
///
/// Returns an error if the stack is empty.
pub fn counter(&self) -> RepeatResult<Word> {
self.stack
.last()
.map(|s| s.counter)
.ok_or(RepeatError::NoCounter)
}
// TODO: Update this comment.
/// If there is a counter on the stack and the counter
/// has greater then 1 repeat left then this will decrement
/// the counter and return the index to repeat to.
///
/// If the counter is 1 then this will pop the counter and
/// return None because the repeat is done.
///
/// If called when the stack is empty then this will return
/// an error.
///
/// Note that because the code has run once before the
/// `RepeatEnd` is hit then we stop at 1.
pub fn repeat(&mut self) -> RepeatResult<Option<usize>> {
let slot = self.stack.last_mut().ok_or(RepeatError::Empty)?;
match slot.limit {
Direction::Up(limit) => {
if slot.counter >= limit.saturating_sub(1) {
self.stack.pop();
Ok(None)
} else {
slot.counter += 1;
Ok(Some(slot.repeat_index))
}
}
Direction::Down => {
if slot.counter <= 1 {
self.stack.pop();
Ok(None)
} else {
slot.counter -= 1;
Ok(Some(slot.repeat_index))
}
}
}
}
}