iterable trace

Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
-members = ["crates/prover"]
+members = ["crates/prover", "crates/air_utils"]
 resolver = "2"
 
 [workspace.package]

crates/air_utils/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "stwo-air-utils"
+version.workspace = true
+edition.workspace = true
+
+[dependencies]
+bytemuck.workspace = true
+itertools.workspace = true
+stwo-prover = { path = "../prover" }
+
+[lib]
+bench = false

crates/air_utils/src/lib.rs

@@ -0,0 +1,2 @@
+#![feature(exact_size_is_empty, raw_slice_split, portable_simd)]
+pub mod trace;

crates/air_utils/src/trace/component_trace.rs

@@ -0,0 +1,127 @@
+use std::marker::PhantomData;
+
+use bytemuck::Zeroable;
+use stwo_prover::core::backend::simd::m31::{PackedM31, LOG_N_LANES, N_LANES};
+use stwo_prover::core::backend::simd::SimdBackend;
+use stwo_prover::core::fields::m31::M31;
+use stwo_prover::core::poly::circle::CircleEvaluation;
+use stwo_prover::core::poly::BitReversedOrder;
+
+/// A 2D Matrix of [`PackedM31`] values.
+/// Used for generating the witness of 'Stwo' proofs.
+/// Stored as an array of `N` columns, each column is a vector of [`PackedM31`] values.
+/// Exposes an iterator over mutable references to the rows of the matrix.
+///
+/// # Example:
+///
+///  ```text
+/// Computation trace of a^2 + (a + 1)^2 for a in 0..256
+/// ```
+/// ```
+/// use stwo_air_utils::trace::component_trace::ComponentTrace;
+/// use itertools::Itertools;
+/// use stwo_prover::core::backend::simd::m31::{PackedM31, N_LANES};
+/// use stwo_prover::core::fields::m31::M31;
+/// use stwo_prover::core::fields::FieldExpOps;
+///
+/// const N_COLUMNS: usize = 3;
+/// const LOG_SIZE: u32 = 8;
+/// let mut trace = ComponentTrace::<N_COLUMNS>::zeroed(LOG_SIZE);
+/// let example_input = (0..1 << LOG_SIZE).map(M31::from).collect_vec(); // 0..256
+/// trace
+///     .iter_mut()
+///     .zip(example_input.chunks(N_LANES))
+///     .chunks(4)
+///     .into_iter()
+///     .for_each(|chunk| {
+///         chunk.into_iter().for_each(|(row, input)| {
+///             *row[0] = PackedM31::from_array(input.try_into().unwrap());
+///             *row[1] = *row[0] + PackedM31::broadcast(M31(1));
+///             *row[2] = row[0].square() + row[1].square();
+///         })
+///     });
+///
+/// let first_3_rows = (0..N_COLUMNS).map(|i| trace.row_at(i)).collect::<Vec<_>>();
+/// assert_eq!(first_3_rows, [[0,1,1], [1,2,5], [2,3,13]].map(|row| row.map(M31::from)));
+/// ```
+#[derive(Debug)]
+pub struct ComponentTrace<const N: usize> {
+    data: [Vec<PackedM31>; N],
+
+    /// Log number of non-packed rows in each column.
+    log_size: u32,
+}
+
+impl<const N: usize> ComponentTrace<N> {
+    pub fn zeroed(log_size: u32) -> Self {
+        let n_simd_elems = 1 << (log_size - LOG_N_LANES);
+        let data = [(); N].map(|_| vec![PackedM31::zeroed(); n_simd_elems]);
+        Self { data, log_size }
+    }
+
+    /// # Safety
+    /// The caller must ensure that the column is populated before being used.
+    #[allow(clippy::uninit_vec)]
+    pub unsafe fn uninitialized(_log_size: u32) -> Self {
+        todo!()
+    }
+
+    pub fn log_size(&self) -> u32 {
+        self.log_size
+    }
+
+    pub fn iter_mut(&mut self) -> RowIterMut<'_, N> {
+        RowIterMut::new(self.data.each_mut().map(|column| column.as_mut_slice()))
+    }
+
+    pub fn to_evals(self) -> [CircleEvaluation<SimdBackend, M31, BitReversedOrder>; N] {
+        todo!()
+    }
+
+    pub fn row_at(&self, row: usize) -> [M31; N] {
+        assert!(row < 1 << self.log_size);
+        let packed_row = row / N_LANES;
+        let idx_in_simd_vector = row % N_LANES;
+        self.data
+            .each_ref()
+            .map(|column| column[packed_row].to_array()[idx_in_simd_vector])
+    }
+}
+
+pub type MutRow<'trace, const N: usize> = [&'trace mut PackedM31; N];
+
+/// An iterator over mutable references to the rows of a [`ComponentTrace`].
+pub struct RowIterMut<'trace, const N: usize> {
+    v: [*mut [PackedM31]; N],
+    phantom: PhantomData<&'trace ()>,
+}
+impl<'trace, const N: usize> RowIterMut<'trace, N> {
+    pub fn new(slice: [&'trace mut [PackedM31]; N]) -> Self {
+        Self {
+            v: slice.map(|s| s as *mut _),
+            phantom: PhantomData,
+        }
+    }
+}
+impl<'trace, const N: usize> Iterator for RowIterMut<'trace, N> {
+    type Item = MutRow<'trace, N>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.v[0].is_empty() {
+            return None;
+        }
+        let item = std::array::from_fn(|i| unsafe {
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (head, tail) = self.v[i].split_at_mut(1);
+            self.v[i] = tail;
+            &mut (*head)[0]
+        });
+        Some(item)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.v[0].len();
+        (len, Some(len))
+    }
+}
+impl<const N: usize> ExactSizeIterator for RowIterMut<'_, N> {}

crates/air_utils/src/trace/mod.rs

@@ -0,0 +1 @@
+pub mod component_trace;