From b5ed27e624322b368b282c1ab7c847d6c617508c Mon Sep 17 00:00:00 2001
From: John Guibas <jtguibas@gmail.com>
Date: Thu, 23 May 2024 17:49:39 -0700
Subject: [PATCH] hm

---
 core/src/stark/verifier.rs     | 14 +++++++++++++-
 recursion/program/src/stark.rs | 19 +++++++------------
 2 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/core/src/stark/verifier.rs b/core/src/stark/verifier.rs
index 6f5bad846d..17e3753336 100644
--- a/core/src/stark/verifier.rs
+++ b/core/src/stark/verifier.rs
@@ -176,7 +176,6 @@ impl<SC: StarkGenericConfig, A: MachineAir<Val<SC>>> Verifier<SC, A> {
             .map_err(|e| VerificationError::InvalidopeningArgument(e))?;
 
         // Verify the constrtaint evaluations.
-
         for (chip, trace_domain, qc_domains, values) in izip!(
             chips.iter(),
             trace_domains,
@@ -199,6 +198,12 @@ impl<SC: StarkGenericConfig, A: MachineAir<Val<SC>>> Verifier<SC, A> {
             )
             .map_err(|_| VerificationError::OodEvaluationMismatch(chip.name()))?;
         }
+
+        let nb_cpu_chips = chips.iter().filter(|chip| chip.name() == "CPU").count();
+        if nb_cpu_chips != 1 {
+            return Err(VerificationError::MissingCpuChip);
+        }
+
         Ok(())
     }
 
@@ -411,6 +416,7 @@ pub enum VerificationError<SC: StarkGenericConfig> {
     OodEvaluationMismatch(String),
     /// The shape of the opening arguments is invalid.
     OpeningShapeError(String, OpeningShapeError),
+    MissingCpuChip,
 }
 
 impl Debug for OpeningShapeError {
@@ -474,6 +480,9 @@ impl<SC: StarkGenericConfig> Debug for VerificationError<SC> {
             VerificationError::OpeningShapeError(chip, e) => {
                 write!(f, "Invalid opening shape for chip {}: {:?}", chip, e)
             }
+            VerificationError::MissingCpuChip => {
+                write!(f, "Missing CPU chip")
+            }
         }
     }
 }
@@ -490,6 +499,9 @@ impl<SC: StarkGenericConfig> Display for VerificationError<SC> {
             VerificationError::OpeningShapeError(chip, e) => {
                 write!(f, "Invalid opening shape for chip {}: {}", chip, e)
             }
+            VerificationError::MissingCpuChip => {
+                write!(f, "Missing CPU chip in shard")
+            }
         }
     }
 }
diff --git a/recursion/program/src/stark.rs b/recursion/program/src/stark.rs
index a7cdd1fb53..ebff884623 100644
--- a/recursion/program/src/stark.rs
+++ b/recursion/program/src/stark.rs
@@ -97,11 +97,7 @@ impl<'a, SC: StarkGenericConfig, A: MachineAir<SC::Val>> VerifyingKeyHint<'a, SC
 impl<C: Config, SC: StarkGenericConfig, A> StarkRecursiveVerifier<C> for StarkMachine<SC, A>
 where
     C::F: TwoAdicField,
-    SC: StarkGenericConfig<
-        Val = C::F,
-        Challenge = C::EF,
-        Domain = TwoAdicMultiplicativeCoset<C::F>,
-    >,
+    SC: StarkGenericConfig<Val = C::F, Challenge = C::EF, Domain = TwoAdicMultiplicativeCoset<C::F>>,
     A: MachineAir<C::F> + for<'a> Air<RecursiveVerifierConstraintFolder<'a, C>>,
     C::F: TwoAdicField,
     C::EF: TwoAdicField,
@@ -148,11 +144,7 @@ pub type RecursiveVerifierConstraintFolder<'a, C> = GenericVerifierConstraintFol
 impl<C: Config, SC: StarkGenericConfig> StarkVerifier<C, SC>
 where
     C::F: TwoAdicField,
-    SC: StarkGenericConfig<
-        Val = C::F,
-        Challenge = C::EF,
-        Domain = TwoAdicMultiplicativeCoset<C::F>,
-    >,
+    SC: StarkGenericConfig<Val = C::F, Challenge = C::EF, Domain = TwoAdicMultiplicativeCoset<C::F>>,
 {
     pub fn verify_shard<A>(
         builder: &mut Builder<C>,
@@ -346,14 +338,17 @@ where
         // TODO CONSTRAIN: that the preprocessed chips get called with verify_constraints.
         builder.cycle_tracker("stage-e-verify-constraints");
         for (i, chip) in machine.chips().iter().enumerate() {
-            let chip_name = chip.name();
-            tracing::debug!("verifying constraints for chip: {}", chip_name);
+            tracing::debug!("verifying constraints for chip: {}", chip.name());
             let index = builder.get(&proof.sorted_idxs, i);
 
             if chip.preprocessed_width() > 0 {
                 builder.assert_var_ne(index, C::N::from_canonical_usize(EMPTY));
             }
 
+            if chip.name() == "CPU" {
+                builder.assert_var_ne(index, C::N::from_canonical_usize(EMPTY));
+            }
+
             builder
                 .if_ne(index, C::N::from_canonical_usize(EMPTY))
                 .then(|builder| {