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feat: add tests and modify doc
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@Eikix
Eikix committed Sep 26, 2023
1 parent 229c540 commit 9a5997c
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Showing 3 changed files with 216 additions and 63 deletions.
51 changes: 28 additions & 23 deletions crates/evm/src/memory.cairo
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,8 @@ use utils::{
};
use debug::PrintTrait;

const MEMORY_SEGMENT_SIZE: usize = 125000;
// 2**17
const MEMORY_SEGMENT_SIZE: usize = 131072;


#[derive(Destruct, Default)]
Expand All @@ -27,7 +28,7 @@ struct Memory {

trait MemoryTrait {
fn new() -> Memory;
fn from_active_segment(active_segment: usize) -> Memory;
fn with_active_segment(active_segment: usize) -> Memory;
fn size(ref self: Memory) -> usize;
fn active_segment(ref self: Memory) -> felt252;
fn store(ref self: Memory, element: u256, offset: usize);
Expand All @@ -47,9 +48,9 @@ impl MemoryImpl of MemoryTrait {
Memory { active_segment: 0, items: Default::default(), bytes_len: Default::default() }
}

/// Initializes a new `Memory` instance.
/// Initializes a new `Memory` instance with a specific active segment
#[inline(always)]
fn from_active_segment(active_segment: usize) -> Memory {
fn with_active_segment(active_segment: usize) -> Memory {
Memory {
active_segment: active_segment, items: Default::default(), bytes_len: Default::default()
}
Expand Down Expand Up @@ -78,10 +79,10 @@ impl MemoryImpl of MemoryTrait {

// Compute actual offset in the dict, given active_segment of Memory (current Execution Context id)
// And Memory Segment Size
let offset = self.compute_active_segment_offset(offset);
let internal_offset = self.compute_active_segment_offset(offset);

// Check alignment of offset to bytes16 chunks
let (chunk_index, offset_in_chunk) = u32_safe_divmod(offset, u32_as_non_zero(16));
let (chunk_index, offset_in_chunk) = u32_safe_divmod(internal_offset, u32_as_non_zero(16));

if offset_in_chunk == 0 {
// Offset is aligned. This is the simplest and most efficient case,
Expand Down Expand Up @@ -114,10 +115,10 @@ impl MemoryImpl of MemoryTrait {

// Compute actual offset in Memory, given active_segment of Memory (current Execution Context id)
// And Memory Segment Size
let offset = self.compute_active_segment_offset(offset);
let internal_offset = self.compute_active_segment_offset(offset);

// Get offset's memory word index and left-based offset of byte in word.
let (chunk_index, left_offset) = u32_safe_divmod(offset, u32_as_non_zero(16));
let (chunk_index, left_offset) = u32_safe_divmod(internal_offset, u32_as_non_zero(16));

// As the memory words are in big-endian order, we need to convert our left-based offset
// to a right-based one.a
Expand Down Expand Up @@ -157,12 +158,14 @@ impl MemoryImpl of MemoryTrait {

// Compute the offset inside the Memory, given its active segment, following the formula:
// index = offset + self.active_segment * 125000
let offset = self.compute_active_segment_offset(offset);
let internal_offset = self.compute_active_segment_offset(offset);

// Check alignment of offset to bytes16 chunks.
let (initial_chunk, offset_in_chunk_i) = u32_safe_divmod(offset, u32_as_non_zero(16));
let (initial_chunk, offset_in_chunk_i) = u32_safe_divmod(
internal_offset, u32_as_non_zero(16)
);
let (final_chunk, mut offset_in_chunk_f) = u32_safe_divmod(
offset + elements.len() - 1, u32_as_non_zero(16)
internal_offset + elements.len() - 1, u32_as_non_zero(16)
);
offset_in_chunk_f += 1;
let mask_i: u256 = helpers::pow256_rev(offset_in_chunk_i);
Expand Down Expand Up @@ -244,10 +247,6 @@ impl MemoryImpl of MemoryTrait {
fn load(ref self: Memory, offset: usize) -> u256 {
self.ensure_length(32 + offset);

// Compute the offset inside the Memory, given its active segment, following the formula:
// index = offset + self.active_segment * 125000
let offset = self.compute_active_segment_offset(offset);

self.load_internal(offset)
}

Expand All @@ -256,10 +255,6 @@ impl MemoryImpl of MemoryTrait {
fn load_n(ref self: Memory, elements_len: usize, ref elements: Array<u8>, offset: usize) {
self.ensure_length(elements_len + offset);

// Compute the offset inside the Memory, given its active segment, following the formula:
// index = offset + self.active_segment * 125000
let offset = self.compute_active_segment_offset(offset);

self.load_n_internal(elements_len, ref elements, offset);
}

Expand Down Expand Up @@ -426,9 +421,13 @@ impl InternalMemoryMethods of InternalMemoryTrait {
/// The `u256` element at the specified offset in the memory chunk.
#[inline(always)]
fn load_internal(ref self: Memory, offset: usize) -> u256 {
let (chunk_index, offset_in_chunk) = u32_safe_divmod(offset, u32_as_non_zero(16));
// Compute the offset inside the dict, given its active segment, following the formula:
// index = offset + self.active_segment * 125000
let internal_offset = self.compute_active_segment_offset(offset);

let (chunk_index, offset_in_chunk) = u32_safe_divmod(internal_offset, u32_as_non_zero(16));

if offset == 0 {
if offset_in_chunk == 0 {
// Offset is aligned. This is the simplest and most efficient case,
// so we optimize for it. Note that no locals were allocated at all.
return self.items.read_u256(chunk_index);
Expand Down Expand Up @@ -480,10 +479,16 @@ impl InternalMemoryMethods of InternalMemoryTrait {
return;
}

// Compute the offset inside the Memory, given its active segment, following the formula:
// index = offset + self.active_segment * 125000
let internal_offset = self.compute_active_segment_offset(offset);

// Check alignment of offset to bytes16 chunks.
let (initial_chunk, offset_in_chunk_i) = u32_safe_divmod(offset, u32_as_non_zero(16));
let (initial_chunk, offset_in_chunk_i) = u32_safe_divmod(
internal_offset, u32_as_non_zero(16)
);
let (final_chunk, mut offset_in_chunk_f) = u32_safe_divmod(
offset + elements_len - 1, u32_as_non_zero(16)
internal_offset + elements_len - 1, u32_as_non_zero(16)
);
offset_in_chunk_f += 1;
let mask_i: u256 = helpers::pow256_rev(offset_in_chunk_i);
Expand Down
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