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use crate::HashMap;
use crate::ast::{Expr, ExprRef, ExprSet};
const DEBUG: bool = false;
macro_rules! debug {
($($arg:tt)*) => {
if DEBUG {
eprint!(" ");
eprintln!($($arg)*);
}
};
}
/// Memoization cache for derivative computations.
///
/// Stores previously computed derivatives keyed by `(ExprRef, byte)` pairs to
/// avoid redundant work during DFA construction.
#[derive(Clone)]
pub struct DerivCache {
pub num_deriv: usize,
state_table: HashMap<(ExprRef, u8), ExprRef>,
}
impl Default for DerivCache {
fn default() -> Self {
Self::new()
}
}
impl DerivCache {
pub fn new() -> Self {
DerivCache {
num_deriv: 0,
state_table: HashMap::default(),
}
}
pub fn derivative(&mut self, exprs: &mut ExprSet, r: ExprRef, b: u8) -> ExprRef {
// This kicks in for lexers with lots of keywords, that is regexps that are
// just concats of single bytes.
// Most of these do not match, so this provides very significant speedup.
// TODO add a flag on exprs to see if this even applies?
match exprs.get(r) {
Expr::Concat(_, args) => {
if exprs.get(args[0]).surely_no_match(b) {
return ExprRef::NO_MATCH;
}
}
// Expr::Repeat(_, e, _, _) => {
// if exprs.get(e).surely_no_match(b) {
// return ExprRef::NO_MATCH;
// }
// }
e => {
if e.surely_no_match(b) {
return ExprRef::NO_MATCH;
}
}
}
let mut or_branches = vec![];
// regular path
exprs.map(
r,
&mut self.state_table,
true,
|r| (r, b),
|exprs, deriv, r| {
let e = exprs.get(r);
self.num_deriv += 1;
let d = match e {
Expr::EmptyString | Expr::NoMatch | Expr::ByteSet(_) | Expr::Byte(_) => {
if e.matches_byte(b) {
ExprRef::EMPTY_STRING
} else {
ExprRef::NO_MATCH
}
}
Expr::ByteConcat(_, bytes, tail) => {
if bytes[0] == b {
let copy = bytes[1..].to_vec();
exprs.mk_byte_concat(©, tail)
} else {
ExprRef::NO_MATCH
}
}
Expr::RemainderIs {
divisor,
remainder,
scale,
fractional_part,
} => {
if let Some(idx) = exprs.digits.iter().position(|&x| x == b) {
let (remainder, scale) = if !fractional_part {
(remainder * 10, scale)
} else {
if scale == 0 {
// Dead code?
return ExprRef::NO_MATCH;
}
(remainder, scale - 1)
};
exprs.mk_remainder_is(
divisor,
(remainder + (idx as u32) * 10_u32.pow(scale)) % divisor,
scale,
fractional_part,
)
} else if b == exprs.digit_dot && !fractional_part && scale > 0 {
exprs.mk_remainder_is(divisor, remainder, scale, true)
} else {
ExprRef::NO_MATCH
}
}
Expr::And(_, _) => exprs.mk_and(deriv),
Expr::Or(_, _) => exprs.mk_or(deriv),
Expr::Not(_, _) => exprs.mk_not(deriv[0]),
Expr::Repeat(_, e, min, max) => {
if deriv[0] == ExprRef::NO_MATCH {
return ExprRef::NO_MATCH;
}
let max = if max == u32::MAX {
u32::MAX
} else {
max.saturating_sub(1)
};
let tail = exprs.mk_repeat(e, min.saturating_sub(1), max);
exprs.mk_concat(deriv[0], tail)
}
Expr::Concat(_, [a, b]) => {
let d0 = exprs.mk_concat(deriv[0], b);
if exprs.is_nullable(a) {
or_branches.clear();
or_branches.push(d0);
or_branches.push(deriv[1]);
exprs.mk_or(&mut or_branches)
} else {
d0
}
}
Expr::Lookahead(_, e, offset) => {
if e == ExprRef::EMPTY_STRING {
ExprRef::NO_MATCH
} else {
exprs.mk_lookahead(deriv[0], offset + 1)
}
}
};
debug!(
"deriv({}) via {} = {}",
exprs.expr_to_string(r),
exprs.pp().byte_to_string(b),
exprs.expr_to_string(d)
);
d
},
)
}
/// Estimate the size of the regex tables in bytes.
pub fn num_bytes(&self) -> usize {
self.state_table.len() * 8 * std::mem::size_of::<isize>()
}
}