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use num::BigUint;
use num::traits::One;
use digit_slice::{DigitSlice, FromDigits, msb};
use {Shape, Noun, NockError, NockResult};
/// Interface for a virtual machine for Nock code.
///
/// A virtual machine can process Hint operations and accelerate Call
/// operations.
pub trait Nock {
/// Accelerate computation of a formula, if possible.
///
/// Nock `*[a 9 b c]`, will trigger `call(*[a c], *[*[a c] 0 b])`.
/// If call returns a noun, that noun will be used as the result of the
/// Nock evaluation. Otherwise the formula will be evaluated as standard
/// Nock.
///
/// The return value must be exactly the same as you would get for
/// evaluating the formula on the subject with a standard Nock
/// interpreter.
#[allow(unused_variables)]
fn call(&mut self, subject: &Noun, formula: &Noun) -> Option<NockResult> {
None
}
/// Handle a Nock hint.
///
/// Nock `*[a 10 b c]` will trigger `hint(a, b, c)`.
#[allow(unused_variables)]
fn hint(&mut self,
subject: &Noun,
hint: &Noun,
c: &Noun)
-> Result<(), NockError> {
Ok(())
}
/// Evaluate the nock `*[subject formula]`
fn nock_on(&mut self, mut subject: Noun, mut formula: Noun) -> NockResult {
loop {
if let Shape::Cell(ops, tail) = formula.clone().get() {
match ops.as_u32() {
// Axis
Some(0) => return get_axis(&tail, &subject),
// Just
Some(1) => return Ok(tail.clone()),
// Fire
Some(2) => {
match tail.get() {
Shape::Cell(ref b, ref c) => {
let p = try!(self.nock_on(subject.clone(),
(*b).clone()));
let q = try!(self.nock_on(subject,
(*c).clone()));
subject = p;
formula = q;
continue;
}
_ => return Err(NockError(format!("fire"))),
}
}
// Depth
Some(3) => {
let p = try!(self.nock_on(subject.clone(),
(*tail).clone()));
return match p.get() {
Shape::Cell(_, _) => Ok(Noun::from(0u32)),
_ => Ok(Noun::from(1u32)),
};
}
// Bump
Some(4) => {
let p = try!(self.nock_on(subject.clone(),
(*tail).clone()));
return match p.get() {
Shape::Atom(ref x) => {
// TODO: Non-bignum optimization
Ok(Noun::from(BigUint::from_digits(x).unwrap() +
BigUint::one()))
}
_ => Err(NockError(format!("bump"))),
};
}
// Same
Some(5) => {
let p = try!(self.nock_on(subject.clone(),
(*tail).clone()));
return match p.get() {
Shape::Cell(ref a, ref b) => {
if a == b {
// Yes.
return Ok(Noun::from(0u32));
} else {
// No.
return Ok(Noun::from(1u32));
}
}
_ => return Err(NockError(format!("same"))),
};
}
// If
Some(6) => {
if let Some((b, c, d)) = tail.get_122() {
let p = try!(self.nock_on(subject.clone(),
(*b).clone()));
match p.get() {
Shape::Atom(ref x) => {
if x == &0u32.as_digits() {
formula = (*c).clone();
} else if x == &1u32.as_digits() {
formula = (*d).clone();
} else {
return Err(NockError(format!("if")));
}
}
_ => return Err(NockError(format!("if"))),
}
continue;
} else {
return Err(NockError(format!("if")));
}
}
// Compose
Some(7) => {
match tail.get() {
Shape::Cell(ref b, ref c) => {
let p = try!(self.nock_on(subject.clone(),
(*b).clone()));
subject = p;
formula = (*c).clone();
continue;
}
_ => return Err(NockError(format!("compose"))),
}
}
// Push
Some(8) => {
match tail.get() {
Shape::Cell(ref b, ref c) => {
let p = try!(self.nock_on(subject.clone(),
(*b).clone()));
subject = Noun::cell(p, subject);
formula = (*c).clone();
continue;
}
_ => return Err(NockError(format!("push"))),
}
}
// Call
Some(9) => {
match tail.get() {
Shape::Cell(ref axis, ref c) => {
// Construct core.
subject = try!(self.nock_on(subject.clone(),
(*c).clone()));
// Fetch from core using axis.
formula = try!(get_axis(axis, &subject));
if let Some(result) = self.call(&subject,
&formula) {
return result;
}
continue;
}
_ => return Err(NockError(format!("call"))),
}
}
// Hint
Some(10) => {
match tail.get() {
Shape::Cell(ref b, ref c) => {
try!(self.hint(&subject, b, c));
formula = (*c).clone();
continue;
}
_ => return Err(NockError(format!("hint"))),
}
}
// Unhandled opcode
Some(code) => {
return Err(NockError(format!("unknown opcode {}",
code)));
}
None => {
if let Shape::Cell(_, _) = ops.get() {
// Autocons
let a = try!(self.nock_on(subject.clone(),
ops.clone()));
let b = try!(self.nock_on(subject, tail.clone()));
return Ok(Noun::cell(a, b));
} else {
return Err(NockError(format!("autocons")));
}
}
}
} else {
return Err(NockError(format!("nock")));
}
}
}
}
/// Evaluate nock `/[axis subject]`
pub fn get_axis(axis: &Noun, subject: &Noun) -> NockResult {
fn fas(x: &[u8], n: usize, mut subject: &Noun) -> NockResult {
for i in (0..(n - 1)).rev() {
if let Shape::Cell(ref a, ref b) = subject.get() {
if bit(x, i) {
subject = b;
} else {
subject = a;
}
} else {
return Err(NockError(format!("axis")));
}
}
Ok((*subject).clone())
}
#[inline]
fn bit(data: &[u8], pos: usize) -> bool {
data[pos / 8] & (1 << (pos % 8)) != 0
}
match axis.get() {
Shape::Atom(ref x) => {
let start = msb(x);
fas(x, start, subject)
}
_ => Err(NockError(format!("axis"))),
}
}