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Remove initial values from Fibonacci STARK state

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This commit is contained in:
wborgeaud 2022-01-28 13:59:43 +01:00
parent e78630ae81
commit c73f32ef2b
1 changed files with 10 additions and 11 deletions
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21
starky/src/fibonacci_stark.rs
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@ -10,11 +10,9 @@ use crate::stark::Stark;
use crate::vars::{StarkEvaluationTargets, StarkEvaluationVars}; use crate::vars::{StarkEvaluationTargets, StarkEvaluationVars};
/// Toy STARK system used for testing. /// Toy STARK system used for testing.
/// Computes a Fibonacci sequence with inital values `x0, x1` using the transition /// Computes a Fibonacci sequence with state `[x0, x1]` using the state transition
/// `x0 <- x1, x1 <- x0 + x1`. /// `x0 <- x1, x1 <- x0 + x1`.
struct FibonacciStark<F: RichField + Extendable<D>, const D: usize> { struct FibonacciStark<F: RichField + Extendable<D>, const D: usize> {
x0: F,
x1: F,
num_rows: usize, num_rows: usize,
_phantom: PhantomData<F>, _phantom: PhantomData<F>,
} }
@ -25,21 +23,20 @@ impl<F: RichField + Extendable<D>, const D: usize> FibonacciStark<F, D> {
// The second public input is `x1`. // The second public input is `x1`.
const PI_INDEX_X1: usize = 1; const PI_INDEX_X1: usize = 1;
// The third public input is the second element of the last row, which should be equal to the // The third public input is the second element of the last row, which should be equal to the
// `(num_rows + 1)`-th Fibonacci number. // `num_rows`-th Fibonacci number.
const PI_INDEX_RES: usize = 2; const PI_INDEX_RES: usize = 2;
fn new(num_rows: usize, x0: F, x1: F) -> Self { fn new(num_rows: usize) -> Self {
Self { Self {
x0,
x1,
num_rows, num_rows,
_phantom: PhantomData, _phantom: PhantomData,
} }
} }
fn generate_trace(&self) -> Vec<[F; Self::COLUMNS]> { /// Generate the trace using `x0, x1` as inital state values.
fn generate_trace(&self, x0: F, x1: F) -> Vec<[F; Self::COLUMNS]> {
(0..self.num_rows) (0..self.num_rows)
.scan([self.x0, self.x1], |acc, _| { .scan([x0, x1], |acc, _| {
let tmp = *acc; let tmp = *acc;
acc[0] = tmp[1]; acc[0] = tmp[1];
acc[1] = tmp[0] + tmp[1]; acc[1] = tmp[0] + tmp[1];
@ -61,9 +58,11 @@ impl<F: RichField + Extendable<D>, const D: usize> Stark<F, D> for FibonacciStar
FE: FieldExtension<D2, BaseField = F>, FE: FieldExtension<D2, BaseField = F>,
P: PackedField<Scalar = FE>, P: PackedField<Scalar = FE>,
{ {
// Check public inputs.
yield_constr.one_first_row(vars.local_values[0] - vars.public_inputs[Self::PI_INDEX_X0]); yield_constr.one_first_row(vars.local_values[0] - vars.public_inputs[Self::PI_INDEX_X0]);
yield_constr.one_first_row(vars.local_values[1] - vars.public_inputs[Self::PI_INDEX_X1]); yield_constr.one_first_row(vars.local_values[1] - vars.public_inputs[Self::PI_INDEX_X1]);
yield_constr.one_last_row(vars.local_values[1] - vars.public_inputs[Self::PI_INDEX_RES]); yield_constr.one_last_row(vars.local_values[1] - vars.public_inputs[Self::PI_INDEX_RES]);
// x0 <- x1 // x0 <- x1
yield_constr.one(vars.next_values[0] - vars.local_values[1]); yield_constr.one(vars.next_values[0] - vars.local_values[1]);
// x1 <- x0 + x1 // x1 <- x0 + x1
@ -109,8 +108,8 @@ mod tests {
F::ONE, F::ONE,
F::from_canonical_usize(fibonacci(num_rows - 1, 0, 1)), F::from_canonical_usize(fibonacci(num_rows - 1, 0, 1)),
]; ];
let stark = S::new(num_rows, public_inputs[0], public_inputs[1]); let stark = S::new(num_rows);
let trace = stark.generate_trace(); let trace = stark.generate_trace(public_inputs[0], public_inputs[1]);
prove::<F, C, S, D>( prove::<F, C, S, D>(
stark, stark,
config, config,