StackOutputs: introduce pop_*() methods

core/src/stack/outputs.rs

@@ -3,6 +3,8 @@ use super::{
     STACK_TOP_SIZE,
 };
 
+use miden_crypto::hash::rpo::RpoDigest;
+
 // STACK OUTPUTS
 // ================================================================================================
 
@@ -140,6 +142,10 @@ impl StackOutputs {
         overflow
     }
 
+    pub fn iter(&self) -> impl Iterator<Item = Felt> + '_ {
+        self.stack.iter().cloned().map(Felt::from)
+    }
+
     // PUBLIC MUTATORS
     // --------------------------------------------------------------------------------------------
 
@@ -149,6 +155,53 @@ impl StackOutputs {
     pub fn stack_mut(&mut self) -> &mut [u64] {
         &mut self.stack
     }
+
+    /// Pops a field element off the stack. Returns `None` if the stack is empty.
+    pub fn pop_felt(&mut self) -> Option<Felt> {
+        self.stack.pop().map(Into::into)
+    }
+
+    /// Pops a RPO digest off the stack. Returns `None` if not enough elements are on the stack.
+    pub fn pop_digest(&mut self) -> Option<RpoDigest> {
+        let digest_elements: [Felt; 4] = {
+            let digest_elements: Vec<Felt> = (0..4)
+                .map(|_| self.pop_felt())
+                // Elements need to be reversed, since a word `[a, b, c, d]` will be stored on the
+                // stack as `[d, c, b, a]`
+                .rev()
+                .collect::<Option<_>>()?;
+
+            digest_elements.try_into().expect("digest_elements contains 4 elements")
+        };
+
+        Some(digest_elements.into())
+    }
+}
+
+// ITERATOR
+// ================================================================================================
+pub trait StackOutputsIteratorDigest: Iterator<Item = Felt> {
+    fn next_digest(&mut self) -> Option<RpoDigest>;
+}
+
+impl<I> StackOutputsIteratorDigest for I
+where
+    I: Iterator<Item = Felt>,
+{
+    fn next_digest(&mut self) -> Option<RpoDigest> {
+        let digest_elements: [Felt; 4] = {
+            let digest_elements: Vec<Felt> = (0..4)
+                .map(|_| self.next())
+                // Elements need to be reversed, since a word `[a, b, c, d]` will be stored on the
+                // stack as `[d, c, b, a]`
+                .rev()
+                .collect::<Option<_>>()?;
+
+            digest_elements.try_into().expect("digest_elements contains 4 elements")
+        };
+
+        Some(digest_elements.into())
+    }
 }
 
 // HELPER FUNCTIONS

processor/src/trace/mod.rs

@@ -117,6 +117,10 @@ impl ExecutionTrace {
         &self.stack_outputs
     }
 
+    pub fn stack_outputs_mut(&mut self) -> &mut StackOutputs {
+        &mut self.stack_outputs
+    }
+
     /// Returns the initial state of the top 16 stack registers.
     pub fn init_stack_state(&self) -> StackTopState {
         let mut result = [ZERO; STACK_TOP_SIZE];