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// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
use crate::evm;
use crate::util::{Bottom, Interval, Join, JoinInto, JoinLattice};
use std::{cmp, fmt, mem};
// ============================================================================
// Disassembly Context
// ============================================================================
#[derive(Debug, PartialEq)]
pub struct AbstractStack<T: PartialEq> {
// The lower segment of an abstract stack represents a variable
// number of unknown values. An interval is used for a compact
// representation. So, for example, `0..1` represents two
// possible lower segments: `[]` and `[??]`.
lower: Interval<usize>,
// The upper segment represents zero or more concrete values on
// the stack.
upper: Vec<T>,
}
impl<T> AbstractStack<T>
where
T: PartialEq + Copy + JoinLattice,
{
pub fn new(lower: impl Into<Interval<usize>>, upper: Vec<T>) -> Self {
let lower_iv = lower.into();
// Done
Self {
lower: lower_iv,
upper,
}
}
/// Construct an empty stack.
pub fn empty() -> Self {
Self::new(0, Vec::new())
}
/// Determine possible lengths of the stack as an interval
pub fn len(&self) -> Interval<usize> {
self.lower.add(self.upper.len().into())
}
/// Peek nth item on the stack (where `0` is top).
pub fn peek(&self, n: usize) -> T {
// Should never be called on bottom
assert!(self != &Self::BOTTOM);
// Get the nth value!
if n < self.upper.len() {
// Determine stack index
let i = self.upper.len() - (1 + n);
// Extract value
self.upper[i]
} else {
T::TOP
}
}
/// Push an iterm onto this stack.
pub fn push(&mut self, val: T) -> &mut Self {
// Should never be called on bottom
assert!(self != &Self::BOTTOM);
//
if val == T::TOP && self.upper.len() == 0 {
self.lower = self.lower.add(1.into());
} else {
// Pop target address off the stack.
self.upper.push(val);
}
self
}
// Pop a single item off the stack
pub fn pop(&mut self) -> &mut Self {
// Should never be called on bottom
assert!(self != &Self::BOTTOM);
// Pop target address off the stack.
if self.upper.is_empty() {
self.lower = self.lower.sub(1.into());
} else {
self.upper.pop();
}
self
}
/// Determine the minimum length of any stack represented by this
/// abstract stack.
pub fn min_len(&self) -> usize {
self.lower.start + self.upper.len()
}
/// Determine the maximum length of any stack represented by this
/// abstract stack.
pub fn max_len(&self) -> usize {
self.lower.end + self.upper.len()
}
/// Access the array of concrete values represented by this stack
/// (i.e. the _upper_ portion of the stack).
pub fn values<'a>(&'a self) -> &'a [T] {
&self.upper
}
/// Set `ith` item from the top on this stack. Thus, `0` is the
/// top of the stack, etc.
pub fn set(mut self, n: usize, val: T) -> Self {
// Should never be called on bottom
assert!(self != Self::BOTTOM);
// NOTE: inefficient when putting unknown value into lower
// portion.
self.ensure_upper(n + 1);
// Determine stack index
let i = self.upper.len() - (1 + n);
// Set value
self.upper[i] = val;
// Rebalance (which can be necessary is val unknown)
self.rebalance()
}
/// Join two abstract stacks together.
pub fn join(self, other: &AbstractStack<T>) -> Self {
let slen = self.upper.len();
let olen = other.upper.len();
// Determine common upper length
let n = cmp::min(slen, olen);
// Normalise lower segments
let lself = self.lower.add(Interval::from(slen - n));
let lother = other.lower.add(Interval::from(olen - n));
let mut merger = AbstractStack::new(lself.union(&lother), Vec::new());
// Push merged items from upper segment
for i in (0..n).rev() {
let ithself = self.peek(i);
let ithother = other.peek(i);
merger.push(ithself.join(&ithother));
}
// Done
merger
}
/// Rebalance the stack if necessary. This is necessary when the
/// upper portion contains unknown values which can be shifted
/// into the lower portion.
fn rebalance(mut self) -> Self {
let mut i = 0;
// Determine whether any rebalancing necessary.
while i < self.upper.len() {
if self.upper[i] != T::TOP {
break;
}
i = i + 1;
}
// Rebalance only if necessary
if i > 0 {
// Increase lower portion
self.lower = self.lower.add(i.into());
// Decrease upper portion
self.upper.drain(0..i);
}
//
self
}
/// Ensure the upper portion has space for at least `n` elements.
fn ensure_upper(&mut self, n: usize) {
// FIXME: inefficient!!
while n > self.upper.len() {
self.upper.insert(0, T::TOP);
self.lower = self.lower.sub(1.into());
}
}
}
// ==================================================================
// Standard Traits
// ==================================================================
impl<T: PartialEq + Copy + JoinLattice> Default for AbstractStack<T> {
fn default() -> Self {
Self::empty()
}
}
impl<T> Clone for AbstractStack<T>
where
T: PartialEq + Clone,
{
fn clone(&self) -> Self {
AbstractStack {
lower: self.lower.clone(),
upper: self.upper.clone(),
}
}
}
impl<T> fmt::Display for AbstractStack<T>
where
T: Copy + PartialEq + Bottom + fmt::Display,
{
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
if self == &Self::BOTTOM {
write!(f, "_|_")
} else {
write!(f, "({})[", self.lower)?;
for i in 0..self.upper.len() {
write!(f, "{}", self.upper[i])?;
}
write!(f, "]")
}
}
}
// ==================================================================
// Lattice Traits
// ==================================================================
impl<T> Bottom for AbstractStack<T>
where
T: PartialEq + Copy + Bottom,
{
const BOTTOM: Self = Self {
lower: Interval::BOTTOM,
upper: Vec::new(),
};
}
impl<T> JoinInto for AbstractStack<T>
where
T: PartialEq + Copy + JoinLattice,
{
/// Merge an abstract stack into this stack, whilst reporting
/// whether this stack changed or not.
fn join_into(&mut self, other: &AbstractStack<T>) -> bool {
// NOTE: this could be done more efficiently.
let old = self.clone();
let mut tmp = Self::empty();
// Install dummy value to keep self alive
mem::swap(self, &mut tmp);
// Perform merge
*self = tmp.join(other);
// Check for change
*self != old
}
}
// ===================================================================
// evm::Word
// ===================================================================
impl<T: evm::Word> evm::Stack for AbstractStack<T>
where
T: PartialEq + JoinLattice,
{
type Word = T;
/// Determine number of items on stack.
fn len(&self) -> T {
todo!("FIX ME");
}
/// Peek nth item on the stack (where `0` is top).
fn peek(&self, n: usize) -> T {
self.peek(n)
}
/// Push an iterm onto this stack.
fn push(&mut self, val: T) {
self.push(val);
}
/// Pop `n` items of the stack.
fn pop(&mut self, n: usize) {
(0..n).for_each(|_| {
self.pop();
});
}
/// Set nth item on stack
fn set(&mut self, n: usize, item: T) {
if n < self.upper.len() {
let i = self.upper.len() - n;
//
self.upper[i - 1] = item;
} else {
todo!("")
}
}
}