openvm_native_recursion/challenger/
duplex.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
use openvm_native_compiler::{
    ir::{RVar, DIGEST_SIZE, PERMUTATION_WIDTH},
    prelude::{Array, Builder, Config, Ext, Felt, Var},
};
use openvm_stark_backend::p3_field::{AbstractField, Field};

use crate::{
    challenger::{
        CanCheckWitness, CanObserveDigest, CanObserveVariable, CanSampleBitsVariable,
        CanSampleVariable, ChallengerVariable, FeltChallenger,
    },
    digest::DigestVariable,
};

/// Reference: [p3_challenger::DuplexChallenger]
#[derive(Clone)]
pub struct DuplexChallengerVariable<C: Config> {
    pub sponge_state: Array<C, Felt<C::F>>,
    pub nb_inputs: Var<C::N>,
    pub nb_outputs: Var<C::N>,
}

impl<C: Config> DuplexChallengerVariable<C> {
    /// Creates a new duplex challenger with the default state.
    pub fn new(builder: &mut Builder<C>) -> Self {
        let sponge_state = builder.dyn_array(PERMUTATION_WIDTH);

        builder.range(0, sponge_state.len()).for_each(|i, builder| {
            builder.set(&sponge_state, i, C::F::ZERO);
        });

        DuplexChallengerVariable::<C> {
            sponge_state,
            nb_inputs: builder.eval(C::N::ZERO),
            nb_outputs: builder.eval(C::N::ZERO),
        }
    }
    /// Creates a new challenger with the same state as an existing challenger.
    #[allow(dead_code)]
    pub fn copy(&self, builder: &mut Builder<C>) -> Self {
        let sponge_state = builder.dyn_array(PERMUTATION_WIDTH);
        builder.range(0, PERMUTATION_WIDTH).for_each(|i, builder| {
            let element = builder.get(&self.sponge_state, i);
            builder.set(&sponge_state, i, element);
        });
        let nb_inputs = builder.eval(self.nb_inputs);
        let nb_outputs = builder.eval(self.nb_outputs);
        DuplexChallengerVariable::<C> {
            sponge_state,
            nb_inputs,
            nb_outputs,
        }
    }

    /// Asserts that the state of this challenger is equal to the state of another challenger.
    #[allow(dead_code)]
    pub fn assert_eq(&self, builder: &mut Builder<C>, other: &Self) {
        builder.assert_var_eq(self.nb_inputs, other.nb_inputs);
        builder.assert_var_eq(self.nb_outputs, other.nb_outputs);
        builder.range(0, PERMUTATION_WIDTH).for_each(|i, builder| {
            let element = builder.get(&self.sponge_state, i);
            let other_element = builder.get(&other.sponge_state, i);
            builder.assert_felt_eq(element, other_element);
        });
    }

    #[allow(dead_code)]
    pub fn reset(&mut self, builder: &mut Builder<C>) {
        let zero: Var<_> = builder.eval(C::N::ZERO);
        let zero_felt: Felt<_> = builder.eval(C::F::ZERO);
        builder.range(0, PERMUTATION_WIDTH).for_each(|i, builder| {
            builder.set(&self.sponge_state, i, zero_felt);
        });
        builder.assign(&self.nb_inputs, zero);
        builder.assign(&self.nb_outputs, zero);
    }

    pub fn duplexing(&mut self, builder: &mut Builder<C>) {
        builder.assign(&self.nb_inputs, C::N::ZERO);

        builder.poseidon2_permute_mut(&self.sponge_state);

        builder.assign(&self.nb_outputs, C::N::from_canonical_usize(DIGEST_SIZE));
    }

    fn observe(&mut self, builder: &mut Builder<C>, value: Felt<C::F>) {
        builder.assign(&self.nb_outputs, C::N::ZERO);

        builder.set(&self.sponge_state, self.nb_inputs, value);
        builder.assign(&self.nb_inputs, self.nb_inputs + C::N::ONE);

        builder
            .if_eq(self.nb_inputs, C::N::from_canonical_usize(DIGEST_SIZE))
            .then(|builder| {
                self.duplexing(builder);
            })
    }

    fn observe_commitment(&mut self, builder: &mut Builder<C>, commitment: &Array<C, Felt<C::F>>) {
        for i in 0..DIGEST_SIZE {
            let element = builder.get(commitment, i);
            self.observe(builder, element);
        }
    }

    fn sample(&mut self, builder: &mut Builder<C>) -> Felt<C::F> {
        let zero: Var<_> = builder.eval(C::N::ZERO);
        builder.if_ne(self.nb_inputs, zero).then_or_else(
            |builder| {
                self.clone().duplexing(builder);
            },
            |builder| {
                builder.if_eq(self.nb_outputs, zero).then(|builder| {
                    self.clone().duplexing(builder);
                });
            },
        );
        let idx: Var<_> = builder.eval(self.nb_outputs - C::N::ONE);
        let output = builder.get(&self.sponge_state, idx);
        builder.assign(&self.nb_outputs, idx);
        output
    }

    fn sample_ext(&mut self, builder: &mut Builder<C>) -> Ext<C::F, C::EF> {
        let a = self.sample(builder);
        let b = self.sample(builder);
        let c = self.sample(builder);
        let d = self.sample(builder);
        builder.ext_from_base_slice(&[a, b, c, d])
    }

    fn sample_bits(&mut self, builder: &mut Builder<C>, nb_bits: RVar<C::N>) -> Array<C, Var<C::N>>
    where
        C::N: Field,
    {
        let rand_f = self.sample(builder);
        let bits = builder.num2bits_f(rand_f, C::N::bits() as u32);

        builder.range(nb_bits, bits.len()).for_each(|i, builder| {
            builder.set(&bits, i, C::N::ZERO);
        });

        bits
    }

    pub fn check_witness(&mut self, builder: &mut Builder<C>, nb_bits: usize, witness: Felt<C::F>) {
        self.observe(builder, witness);
        let element_bits = self.sample_bits(builder, RVar::from(nb_bits));
        builder.range(0, nb_bits).for_each(|i, builder| {
            let element = builder.get(&element_bits, i);
            builder.assert_var_eq(element, C::N::ZERO);
        });
    }
}

impl<C: Config> CanObserveVariable<C, Felt<C::F>> for DuplexChallengerVariable<C> {
    fn observe(&mut self, builder: &mut Builder<C>, value: Felt<C::F>) {
        DuplexChallengerVariable::observe(self, builder, value);
    }

    fn observe_slice(&mut self, builder: &mut Builder<C>, values: Array<C, Felt<C::F>>) {
        builder.range(0, values.len()).for_each(|i, builder| {
            let element = builder.get(&values, i);
            self.observe(builder, element);
        });
    }
}

impl<C: Config> CanSampleVariable<C, Felt<C::F>> for DuplexChallengerVariable<C> {
    fn sample(&mut self, builder: &mut Builder<C>) -> Felt<C::F> {
        DuplexChallengerVariable::sample(self, builder)
    }
}

impl<C: Config> CanSampleBitsVariable<C> for DuplexChallengerVariable<C> {
    fn sample_bits(
        &mut self,
        builder: &mut Builder<C>,
        nb_bits: RVar<C::N>,
    ) -> Array<C, Var<C::N>> {
        DuplexChallengerVariable::sample_bits(self, builder, nb_bits)
    }
}

impl<C: Config> CanObserveDigest<C> for DuplexChallengerVariable<C> {
    fn observe_digest(&mut self, builder: &mut Builder<C>, commitment: DigestVariable<C>) {
        if let DigestVariable::Felt(commitment) = commitment {
            self.observe_commitment(builder, &commitment);
        } else {
            panic!("Expected a felt digest");
        }
    }
}

impl<C: Config> FeltChallenger<C> for DuplexChallengerVariable<C> {
    fn sample_ext(&mut self, builder: &mut Builder<C>) -> Ext<C::F, C::EF> {
        DuplexChallengerVariable::sample_ext(self, builder)
    }
}

impl<C: Config> CanCheckWitness<C> for DuplexChallengerVariable<C> {
    fn check_witness(&mut self, builder: &mut Builder<C>, nb_bits: usize, witness: Felt<C::F>) {
        DuplexChallengerVariable::check_witness(self, builder, nb_bits, witness);
    }
}

impl<C: Config> ChallengerVariable<C> for DuplexChallengerVariable<C> {
    fn new(builder: &mut Builder<C>) -> Self {
        DuplexChallengerVariable::new(builder)
    }
}

#[cfg(test)]
mod tests {
    use openvm_native_circuit::execute_program;
    use openvm_native_compiler::{
        asm::{AsmBuilder, AsmConfig},
        ir::Felt,
    };
    use openvm_stark_backend::{
        config::{StarkGenericConfig, Val},
        p3_challenger::{CanObserve, CanSample},
        p3_field::AbstractField,
    };
    use openvm_stark_sdk::{
        config::baby_bear_poseidon2::{default_engine, BabyBearPoseidon2Config},
        engine::StarkEngine,
        p3_baby_bear::BabyBear,
    };
    use rand::Rng;

    use super::DuplexChallengerVariable;

    fn test_compiler_challenger_with_num_challenges(num_challenges: usize) {
        let mut rng = rand::thread_rng();
        let observations = (0..num_challenges)
            .map(|_| BabyBear::from_canonical_u32(rng.gen_range(0..(1 << 30))))
            .collect::<Vec<_>>();

        type SC = BabyBearPoseidon2Config;
        type F = Val<SC>;
        type EF = <SC as StarkGenericConfig>::Challenge;

        let engine = default_engine();
        let mut challenger = engine.new_challenger();
        for observation in &observations {
            challenger.observe(*observation);
        }
        let result: F = challenger.sample();
        println!("expected result: {}", result);

        let mut builder = AsmBuilder::<F, EF>::default();

        let mut challenger = DuplexChallengerVariable::<AsmConfig<F, EF>>::new(&mut builder);
        for observation in &observations {
            let observation: Felt<_> = builder.eval(*observation);
            challenger.observe(&mut builder, observation);
        }
        let element = challenger.sample(&mut builder);

        let expected_result: Felt<_> = builder.eval(result);
        builder.assert_felt_eq(expected_result, element);

        builder.halt();

        let program = builder.compile_isa();
        execute_program(program, vec![]);
    }

    #[test]
    fn test_compiler_challenger() {
        test_compiler_challenger_with_num_challenges(1);
        test_compiler_challenger_with_num_challenges(4);
        test_compiler_challenger_with_num_challenges(8);
        test_compiler_challenger_with_num_challenges(10);
        test_compiler_challenger_with_num_challenges(16);
        test_compiler_challenger_with_num_challenges(20);
        test_compiler_challenger_with_num_challenges(50);
    }
}