openvm_circuit_primitives/range_gate/
mod.rs

1//! Range check for a fixed bit size without using preprocessed trace.
2//!
3//! Caution: We almost always prefer to use the
4//! [VariableRangeCheckerChip](super::var_range::VariableRangeCheckerChip) instead of this chip.
5
6use std::{
7    borrow::Borrow,
8    mem::{size_of, transmute},
9    sync::atomic::AtomicU32,
10};
11
12use openvm_circuit_primitives_derive::AlignedBorrow;
13use openvm_stark_backend::{
14    interaction::{BusIndex, InteractionBuilder},
15    p3_air::{Air, AirBuilder, BaseAir},
16    p3_field::{Field, PrimeCharacteristicRing},
17    p3_matrix::{dense::RowMajorMatrix, Matrix},
18    p3_util::indices_arr,
19    BaseAirWithPublicValues, PartitionedBaseAir,
20};
21
22pub use crate::range::RangeCheckBus;
23use crate::{ColumnsAir, StructReflection, StructReflectionHelper};
24
25#[cfg(test)]
26mod tests;
27
28#[repr(C)]
29#[derive(Copy, Clone, Default, AlignedBorrow, StructReflection)]
30pub struct RangeGateCols<T> {
31    /// Column with sequential values from 0 to range_max-1
32    pub counter: T,
33    /// Number of range checks requested for each value
34    pub mult: T,
35}
36
37impl<T: Clone> RangeGateCols<T> {
38    pub fn from_slice(slice: &[T]) -> Self {
39        let counter = slice[0].clone();
40        let mult = slice[1].clone();
41
42        Self { counter, mult }
43    }
44}
45
46pub const NUM_RANGE_GATE_COLS: usize = size_of::<RangeGateCols<u8>>();
47pub const RANGE_GATE_COL_MAP: RangeGateCols<usize> = make_col_map();
48
49#[derive(Clone, Copy, Debug, derive_new::new, ColumnsAir)]
50#[columns_via(RangeGateCols<u8>)]
51pub struct RangeCheckerGateAir {
52    pub bus: RangeCheckBus,
53}
54
55impl<F: Field> BaseAirWithPublicValues<F> for RangeCheckerGateAir {}
56impl<F: Field> PartitionedBaseAir<F> for RangeCheckerGateAir {}
57impl<F: Field> BaseAir<F> for RangeCheckerGateAir {
58    fn width(&self) -> usize {
59        NUM_RANGE_GATE_COLS
60    }
61}
62
63impl<AB: InteractionBuilder> Air<AB> for RangeCheckerGateAir {
64    fn eval(&self, builder: &mut AB) {
65        let main = builder.main();
66
67        let (local, next) = (
68            main.row_slice(0).expect("window should have two elements"),
69            main.row_slice(1).expect("window should have two elements"),
70        );
71        let local: &RangeGateCols<AB::Var> = (*local).borrow();
72        let next: &RangeGateCols<AB::Var> = (*next).borrow();
73
74        // Ensure counter starts at 0
75        builder
76            .when_first_row()
77            .assert_eq(local.counter, AB::Expr::ZERO);
78        // Ensure counter increments by 1 in each row
79        builder
80            .when_transition()
81            .assert_eq(local.counter + AB::Expr::ONE, next.counter);
82        // Constrain the last counter value to ensure trace height equals range_max
83        // This is critical as the trace height is not part of the verification key
84        builder
85            .when_last_row()
86            .assert_eq(local.counter, AB::F::from_u32(self.bus.range_max - 1));
87        // Omit creating separate bridge.rs file for brevity
88        self.bus.receive(local.counter).eval(builder, local.mult);
89    }
90}
91
92/// This chip gets requests to verify that a number is in the range
93/// [0, MAX). In the trace, there is a counter column and a multiplicity
94/// column. The counter column is generated using a gate, as opposed to
95/// the other RangeCheckerChip.
96pub struct RangeCheckerGateChip {
97    pub air: RangeCheckerGateAir,
98    pub count: Vec<AtomicU32>,
99}
100
101impl RangeCheckerGateChip {
102    pub fn new(bus: RangeCheckBus) -> Self {
103        let count = (0..bus.range_max).map(|_| AtomicU32::new(0)).collect();
104
105        Self {
106            air: RangeCheckerGateAir::new(bus),
107            count,
108        }
109    }
110
111    pub fn bus(&self) -> RangeCheckBus {
112        self.air.bus
113    }
114
115    pub fn bus_index(&self) -> BusIndex {
116        self.air.bus.inner.index
117    }
118
119    pub fn range_max(&self) -> u32 {
120        self.air.bus.range_max
121    }
122
123    pub fn air_width(&self) -> usize {
124        2
125    }
126
127    pub fn add_count(&self, val: u32) {
128        assert!(
129            val < self.range_max(),
130            "range exceeded: {} >= {}",
131            val,
132            self.range_max()
133        );
134        let val_atomic = &self.count[val as usize];
135        val_atomic.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
136    }
137
138    pub fn clear(&self) {
139        for i in 0..self.count.len() {
140            self.count[i].store(0, std::sync::atomic::Ordering::Relaxed);
141        }
142    }
143
144    pub fn generate_trace<F: Field>(&self) -> RowMajorMatrix<F> {
145        let rows = self
146            .count
147            .iter()
148            .enumerate()
149            .flat_map(|(i, count)| {
150                let c = count.swap(0, std::sync::atomic::Ordering::Relaxed);
151                vec![F::from_usize(i), F::from_u32(c)]
152            })
153            .collect();
154        RowMajorMatrix::new(rows, NUM_RANGE_GATE_COLS)
155    }
156}
157
158const fn make_col_map() -> RangeGateCols<usize> {
159    let indices_arr = indices_arr::<NUM_RANGE_GATE_COLS>();
160    // SAFETY: RangeGateCols is repr(C) with two fields, same layout as [usize; 2].
161    // NUM_RANGE_GATE_COLS equals 2. Transmute reinterprets array as struct.
162    unsafe { transmute::<[usize; NUM_RANGE_GATE_COLS], RangeGateCols<usize>>(indices_arr) }
163}
openvm_circuit_primitives/range_gate/mod.rs

openvm_circuit_primitives/range_gate/
mod.rs
