Check: is DynVolatileRamTable::max_len broken?

scroll-tech · Dec 9, 2024 · d9cc59b · d9cc59b
1 parent c4a6f09
commit d9cc59b
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Showing 2 changed files with 15 additions and 1 deletion.
diff --git a/ceno_zkvm/src/tables/ram.rs b/ceno_zkvm/src/tables/ram.rs
@@ -31,6 +31,15 @@ impl DynVolatileRamTable for DynMemTable {
     }
 }
 
+#[test]
+fn test_dyn_mem_table() {
+    let mut params = ProgramParams::default();
+    params.platform.ram.start = 0;
+    params.platform.ram.end = 100;
+    let max_len_bytes = 4 * DynMemTable::max_len(&params);
+    assert_eq!(max_len_bytes, 128);
+}
+
 pub type DynMemCircuit<E> = DynVolatileRamCircuit<E, DynMemTable>;
 
 #[derive(Clone)]

diff --git a/ceno_zkvm/src/tables/ram/ram_circuit.rs b/ceno_zkvm/src/tables/ram/ram_circuit.rs
@@ -163,7 +163,12 @@ pub trait DynVolatileRamTable {
     fn max_len(params: &ProgramParams) -> usize {
         let max_size =
             (Self::end_addr(params) - Self::offset_addr(params)).div_ceil(WORD_SIZE as u32) as Addr;
-        1 << (u32::BITS - 1 - max_size.leading_zeros()) // prev_power_of_2
+        let max_len = 1 << (u32::BITS - 1 - max_size.leading_zeros()); // prev_power_of_2
+        assert!(
+            max_size as usize <= max_len,
+            "Did not round up {max_size} correctly, got {max_len}, which is smaller."
+        );
+        max_len
     }
 
     fn addr(params: &ProgramParams, entry_index: usize) -> Addr {