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refactor: use Nullable<u256> in Stack (#47)
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@enitrat
enitrat authored Aug 3, 2023
1 parent 1fa4060 commit c8887b8
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Showing 4 changed files with 61 additions and 124 deletions.
2 changes: 2 additions & 0 deletions src/errors.cairo
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
const STACK_OVERFLOW: felt252 = 'Kakarot: StackOverflow';
const STACK_UNDERFLOW: felt252 = 'Kakarot: StackUnderflow';
3 changes: 3 additions & 0 deletions src/lib.cairo
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Original file line number Diff line number Diff line change
Expand Up @@ -16,5 +16,8 @@ mod context;
// Utils module
mod utils;

// Errors module
mod errors;

// tests
mod tests;
108 changes: 40 additions & 68 deletions src/stack.cairo
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Original file line number Diff line number Diff line change
Expand Up @@ -17,24 +17,34 @@
// Core lib imports
use dict::Felt252DictTrait;
use option::OptionTrait;
use array::ArrayTrait;
use traits::Into;
use result::ResultTrait;
use array::ArrayTrait;
use kakarot::utils::constants;
use debug::PrintTrait;
use box::BoxTrait;
use nullable::{nullable_from_box, NullableTrait};
use kakarot::errors;


struct Stack {
items: Felt252Dict<u128>,
len: usize,
// This should be in the corelib
trait NullableTraitExt<T> {
fn new(value: T) -> Nullable<T>;
}

impl DestructStack of Destruct<Stack> {
fn destruct(self: Stack) nopanic {
self.items.squash();
impl NullableTraitExtImpl of NullableTraitExt<u256> {
fn new(value: u256) -> Nullable<u256> {
let nullable = nullable_from_box(BoxTrait::new(value));
nullable
}
}

#[derive(Destruct)]
struct Stack {
items: Felt252Dict<Nullable<u256>>,
len: usize,
}

trait StackTrait {
fn new() -> Stack;
fn push(ref self: Stack, item: u256) -> ();
Expand All @@ -53,24 +63,26 @@ impl StackImpl of StackTrait {
/// Returns
/// * Stack The new stack instance.
fn new() -> Stack {
let items: Felt252Dict<u128> = Default::default();
let items: Felt252Dict<Nullable<u256>> = Default::default();
Stack { items, len: 0 }
}

/// Pushes a new item onto the stack.
/// Pushes a new item onto the stack. If this operation would overflow the stack,
/// panics with a StackOverflow error.
/// Parameters
/// * self The stack instance.
/// * item The item to push onto the stack.
fn push(ref self: Stack, item: u256) -> () {
// we can store at most 1024 256-bits words
if self.len() == constants::STACK_MAX_DEPTH {
panic_with_felt252('Kakarot: StackOverflow')
panic_with_felt252(errors::STACK_OVERFLOW)
}
self.insert_u256(item, self.len());
self.items.insert(self.len.into(), NullableTraitExt::new(item));
self.len += 1;
}

/// Pops the top item off the stack.
/// Pops the top item off the stack. If the stack is empty,
/// leaves the stack unchanged.
/// Returns
/// * Option<u256> The popped item, or None if the stack is empty.
fn pop(ref self: Stack) -> Option<u256> {
Expand All @@ -79,7 +91,8 @@ impl StackImpl of StackTrait {
}
let last_index = self.len() - 1;
self.len -= 1;
Option::Some(self.get_u256(last_index))
let item = self.items.get(last_index.into());
Option::Some(item.deref())
}

/// Pops N elements from the stack.
Expand All @@ -91,7 +104,7 @@ impl StackImpl of StackTrait {
/// * Array<u256> An array containing the popped items
fn pop_n(ref self: Stack, mut n: usize) -> Array<u256> {
if n > self.len() {
panic_with_felt252('Kakarot: StackUnderflow');
panic_with_felt252(errors::STACK_UNDERFLOW);
}
let mut popped_items = ArrayTrait::<u256>::new();
loop {
Expand All @@ -112,25 +125,29 @@ impl StackImpl of StackTrait {
Option::None(())
} else {
let last_index = self.len() - 1;
Option::Some(self.get_u256(last_index))
let item = self.items.get(last_index.into());
Option::Some(item.deref())
}
}

/// Peeks at the item at the given index on the stack.
/// index is 0-based, 0 being the top of the stack.
/// If the index is too large, panics with a StackUnderflow error.
/// # Arguments
/// * `self` - the Stack instance
/// * `index` - the index of the item to peek at

///
/// Returns
/// * u256 The item at the given index, or None if the stack is empty.
fn peek_at(ref self: Stack, index: usize) -> u256 {
if index >= self.len() {
panic_with_felt252('Kakarot: StackUnderflow');
panic_with_felt252(errors::STACK_UNDERFLOW);
}

let item = self.get_u256(self.len() - 1 - index);
item
let position = self.len() - 1 - index;
let item = self.items.get(position.into());

item.deref()
}

/// Swaps the item at the given index with the on on the top of the stack.
Expand All @@ -145,10 +162,10 @@ impl StackImpl of StackTrait {
}
let position_0 = self.len() - 1;
let position_item = position_0 - index;
let top_item = self.get_u256(position_0);
let swapped_item = self.get_u256(position_item);
self.insert_u256(top_item, position_item);
self.insert_u256(swapped_item, position_0);
let top_item = self.items.get(position_0.into());
let swapped_item = self.items.get(position_item.into());
self.items.insert(position_0.into(), swapped_item.into());
self.items.insert(position_item.into(), top_item.into());
}

/// Returns the length of the stack.
Expand All @@ -171,48 +188,3 @@ impl StackImpl of StackTrait {
*self.len == 0
}
}

/// Trait for helping with stack operations on 256-bit unsigned integers
trait StackU256HelperTrait {
fn dict_len(ref self: Stack) -> usize;
fn insert_u256(ref self: Stack, item: u256, index: usize);
fn get_u256(ref self: Stack, index: usize) -> u256;
}

/// Implementation of `StackU256HelperTrait`
impl StackU256HelperImpl of StackU256HelperTrait {
/// Returns the length of the dictionary
///
/// # Returns
/// `felt252` - the length of the dictionary
fn dict_len(ref self: Stack) -> usize {
(self.len() * 2)
}

/// Inserts a 256-bit unsigned integer `item` into the stack at the given `index`
///
/// # Arguments
/// * `item` - the 256-bit unsigned integer to insert into the stack
/// * `index` - the index at which to insert the item in the stack
fn insert_u256(ref self: Stack, item: u256, index: usize) {
let real_index: felt252 = index.into() * 2;
self.items.insert(real_index, item.high);
self.items.insert(real_index + 1, item.low);
}

/// Gets a 256-bit unsigned integer from the stack at the given `index`
///
/// # Arguments
/// * `index` - the index of the item to retrieve from the stack
///
/// # Returns
/// `u256` - the 256-bit unsigned integer retrieved from the stack
fn get_u256(ref self: Stack, index: usize) -> u256 {
let real_index: felt252 = index.into() * 2;
let high = self.items.get(real_index.into());
let low = self.items.get(real_index.into() + 1);
let item = u256 { low: low, high: high };
item
}
}

72 changes: 16 additions & 56 deletions src/tests/test_stack.cairo
View file
Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ use kakarot::stack::StackTrait;
use kakarot::utils::constants;

#[test]
#[available_gas(2000000)]
#[available_gas(11500)]
fn test_stack_new_should_return_empty_stack() {
// When
let mut stack = StackTrait::new();
Expand All @@ -20,7 +20,7 @@ fn test_stack_new_should_return_empty_stack() {
}

#[test]
#[available_gas(2000000)]
#[available_gas(40000)]
fn test__empty__should_return_if_stack_is_empty() {
// Given
let mut stack = StackTrait::new();
Expand All @@ -35,7 +35,7 @@ fn test__empty__should_return_if_stack_is_empty() {
}

#[test]
#[available_gas(2000000)]
#[available_gas(35000)]
fn test__len__should_return_the_length_of_the_stack() {
// Given
let mut stack = StackTrait::new();
Expand All @@ -55,7 +55,7 @@ mod push {
use option::OptionTrait;
use super::constants;
#[test]
#[available_gas(2000000)]
#[available_gas(60000)]
fn test_should_add_an_element_to_the_stack() {
// Given
let mut stack = StackTrait::new();
Expand All @@ -72,7 +72,7 @@ mod push {
}

#[test]
#[available_gas(2000000000000000)]
#[available_gas(27000000)]
#[should_panic(expected: ('Kakarot: StackOverflow', ))]
fn test_should_fail_when_overflow() {
// Given
Expand Down Expand Up @@ -101,7 +101,7 @@ mod pop {
use option::OptionTrait;

#[test]
#[available_gas(2000000)]
#[available_gas(95000)]
fn test_should_pop_an_element_from_the_stack() {
// Given
let mut stack = StackTrait::new();
Expand All @@ -118,7 +118,7 @@ mod pop {
}

#[test]
#[available_gas(2000000)]
#[available_gas(220000)]
fn test_should_pop_N_elements_from_the_stack() {
// Given
let mut stack = StackTrait::new();
Expand All @@ -138,7 +138,7 @@ mod pop {
}

#[test]
#[available_gas(2000000)]
#[available_gas(35000)]
fn test_pop_return_none_when_stack_underflow() {
// Given
let mut stack = StackTrait::new();
Expand All @@ -149,7 +149,7 @@ mod pop {
}

#[test]
#[available_gas(2000000)]
#[available_gas(50000)]
#[should_panic(expected: ('Kakarot: StackUnderflow', ))]
fn test_pop_n_should_fail_when_stack_underflow() {
// Given
Expand All @@ -167,7 +167,7 @@ mod peek {
use option::OptionTrait;

#[test]
#[available_gas(2000000)]
#[available_gas(80000)]
fn test_should_return_last_item() {
// Given
let mut stack = StackTrait::new();
Expand All @@ -182,7 +182,7 @@ mod peek {
}

#[test]
#[available_gas(2000000)]
#[available_gas(95000)]
fn test_should_return_stack_at_given_index_when_value_is_0() {
// Given
let mut stack = StackTrait::new();
Expand All @@ -198,7 +198,7 @@ mod peek {
}

#[test]
#[available_gas(2000000)]
#[available_gas(95000)]
fn test_should_return_stack_at_given_index_when_value_is_1() {
// Given
let mut stack = StackTrait::new();
Expand All @@ -214,7 +214,7 @@ mod peek {
}

#[test]
#[available_gas(2000000)]
#[available_gas(35000)]
#[should_panic(expected: ('Kakarot: StackUnderflow', ))]
fn test_should_fail_when_underflow() {
// Given
Expand All @@ -229,7 +229,7 @@ mod peek {
mod swap {
use super::StackTrait;
#[test]
#[available_gas(2000000)]
#[available_gas(400000)]
fn test_should_swap_2_stack_items() {
// Given
let mut stack = StackTrait::new();
Expand Down Expand Up @@ -261,7 +261,7 @@ mod swap {
}

#[test]
#[available_gas(2000000)]
#[available_gas(50000)]
#[should_panic(expected: ('Kakarot: StackUnderflow', ))]
fn test_should_fail_when_index_1_is_underflow() {
// Given
Expand All @@ -272,7 +272,7 @@ mod swap {
}

#[test]
#[available_gas(2000000)]
#[available_gas(60000)]
#[should_panic(expected: ('Kakarot: StackUnderflow', ))]
fn test_should_fail_when_index_2_is_underflow() {
// Given
Expand All @@ -283,43 +283,3 @@ mod swap {
let result = stack.swap_i(2);
}
}


#[cfg(test)]
mod stack_helper_tests {
use super::StackTrait;
use kakarot::stack::StackU256HelperTrait;
use dict::Felt252DictTrait;
use traits::Into;
use debug::PrintTrait;

#[test]
fn test_dict_len() {
let mut stack = StackTrait::new();
stack.len = 1;
let dict_len = stack.dict_len();
assert(dict_len == 2, 'dict length should be 2');
}

#[test]
fn test_insert_u256() {
let mut stack = StackTrait::new();
let expected: u256 = u256 { low: 100, high: 100 };
stack.insert_u256(expected, 0);
let high = stack.items.get(0);
let low = stack.items.get(1);
let actual = u256 { low: low, high: high };
assert(expected == actual, 'u256 not matching expected');
}

#[test]
fn test_get_u256() {
let mut stack = StackTrait::new();
let v1: u256 = 100;
let v2: u256 = 101;
stack.insert_u256(v1, 0);
stack.insert_u256(v2, 1);
let item = stack.get_u256(1);
assert(v2 == item, 'u256 item should be 101');
}
}

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