perf: implement mem_eq and use it for set_add (#1198)

Author: Oppen

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 #### Upcoming Changes
 
+* feat: implement `mem_eq` function to test for equality of two ranges in memory [#1198](https://github.com/lambdaclass/cairo-rs/pull/1198)
+* perf: use `mem_eq` in `set_add` [#1198](https://github.com/lambdaclass/cairo-rs/pull/1198)
+
 * feat: wrap big variants of `HintError`, `VirtualMachineError`, `RunnerError`, `MemoryError`, `MathError`, `InsufficientAllocatedCellsError` in `Box` [#1193](https://github.com/lambdaclass/cairo-rs/pull/1193)
   * BREAKING: all tuple variants of `HintError` with a single `Felt252` or multiple elements now receive a single `Box`
 

src/hint_processor/builtin_hint_processor/set.rs

@@ -11,7 +11,6 @@ use crate::{
     types::errors::math_errors::MathError,
     vm::{errors::hint_errors::HintError, vm_core::VirtualMachine},
 };
-use core::cmp::Ordering;
 use felt::Felt252;
 use num_traits::{One, ToPrimitive, Zero};
 
@@ -41,10 +40,7 @@ pub fn set_add(
     let range_limit = (set_end_ptr - set_ptr)?;
 
     for i in 0..range_limit {
-        if matches!(
-            vm.memcmp(elm_ptr, (set_ptr + elm_size * i)?, elm_size),
-            (Ordering::Equal, _)
-        ) {
+        if vm.mem_eq(elm_ptr, (set_ptr + elm_size * i)?, elm_size) {
             insert_value_from_var_name("index", Felt252::new(i), vm, ids_data, ap_tracking)?;
             return insert_value_from_var_name(
                 "is_elm_in_set",

src/vm/vm_core.rs

@@ -822,6 +822,10 @@ impl VirtualMachine {
         self.segments.memory.memcmp(lhs, rhs, len)
     }
 
+    pub fn mem_eq(&self, lhs: Relocatable, rhs: Relocatable, len: usize) -> bool {
+        self.segments.memory.mem_eq(lhs, rhs, len)
+    }
+
     ///Gets `n_ret` return values from memory
     pub fn get_return_values(&self, n_ret: usize) -> Result<Vec<MaybeRelocatable>, MemoryError> {
         let addr = (self.run_context.get_ap() - n_ret)

src/vm/vm_memory/memory.rs

@@ -398,6 +398,54 @@ impl Memory {
         (Ordering::Equal, len)
     }
 
+    /// Compares two ranges of values in memory of length `len`
+    /// Returns the ordering and the first relative position at which they differ
+    /// Special cases:
+    /// - `lhs` exists in memory but `rhs` doesn't -> (Ordering::Greater, 0)
+    /// - `rhs` exists in memory but `lhs` doesn't -> (Ordering::Less, 0)
+    /// - None of `lhs` or `rhs` exist in memory -> (Ordering::Equal, 0)
+    /// Everything else behaves much like `memcmp` in C.
+    /// This is meant as an optimization for hints to avoid allocations.
+    pub(crate) fn mem_eq(&self, lhs: Relocatable, rhs: Relocatable, len: usize) -> bool {
+        if lhs == rhs {
+            return true;
+        }
+        let get_segment = |idx: isize| {
+            if idx.is_negative() {
+                self.temp_data.get(-(idx + 1) as usize)
+            } else {
+                self.data.get(idx as usize)
+            }
+        };
+        match (
+            get_segment(lhs.segment_index),
+            get_segment(rhs.segment_index),
+        ) {
+            (None, None) => {
+                return true;
+            }
+            (Some(_), None) => {
+                return false;
+            }
+            (None, Some(_)) => {
+                return false;
+            }
+            (Some(lhs_segment), Some(rhs_segment)) => {
+                let (lhs_start, rhs_start) = (lhs.offset, rhs.offset);
+                for i in 0..len {
+                    let (lhs, rhs) = (
+                        lhs_segment.get(lhs_start + i),
+                        rhs_segment.get(rhs_start + i),
+                    );
+                    if lhs != rhs {
+                        return false;
+                    }
+                }
+            }
+        };
+        true
+    }
+
     /// Gets a range of memory values from addr to addr + size
     /// The outputed range may contain gaps if the original memory has them
     pub fn get_range(&self, addr: Relocatable, size: usize) -> Vec<Option<Cow<MaybeRelocatable>>> {