tasm_lib/arithmetic/xfe/
to_the_power_of_power_of_2.rs

use triton_vm::prelude::*;

use crate::data_type::DataType;
use crate::library::Library;
use crate::traits::basic_snippet::BasicSnippet;

pub struct ToThePowerOfPowerOf2;

impl BasicSnippet for ToThePowerOfPowerOf2 {
    fn inputs(&self) -> Vec<(DataType, String)> {
        vec![
            (DataType::U32, "log_2_exponent".to_owned()),
            (DataType::Xfe, "base".to_owned()),
        ]
    }

    fn outputs(&self) -> Vec<(DataType, String)> {
        vec![(DataType::Xfe, "result".to_owned())]
    }

    fn entrypoint(&self) -> String {
        "tasmlib_arithmetic_xfe_to_the_power_of_power_of_2".to_owned()
    }

    fn code(&self, _library: &mut Library) -> Vec<LabelledInstruction> {
        let entrypoint = self.entrypoint();

        let loop_label = format!("{}_loop", entrypoint);
        let loop_code = triton_asm!(
            // INVARIANT: _ remainder [acc]
            {loop_label}:
                // end condition: remainder == 0
                dup 3
                push 0
                eq
                skiz
                    return

                // _ remainder [acc]
                dup 2
                dup 2
                dup 2
                xx_mul
                // _ remainder [acc^2]

                swap 3
                push -1
                add
                swap 3
                // _ (remainder - 1) [acc^2]

                recurse

        );

        triton_asm!(
            {entrypoint}:
                call {loop_label}

                swap 1
                swap 2
                swap 3
                pop 1

                return

            {&loop_code}
        )
    }
}

#[cfg(test)]
mod tests {
    use itertools::Itertools;
    use rand::prelude::*;
    use triton_vm::prelude::*;
    use triton_vm::twenty_first::math::traits::ModPowU32;

    use super::*;
    use crate::arithmetic::xfe::mod_pow_u32_generic::XfeModPowU32Generic;
    use crate::snippet_bencher::BenchmarkCase;
    use crate::test_helpers::test_rust_equivalence_given_complete_state;
    use crate::traits::closure::Closure;
    use crate::traits::closure::ShadowedClosure;
    use crate::traits::rust_shadow::RustShadow;

    impl Closure for ToThePowerOfPowerOf2 {
        fn rust_shadow(&self, stack: &mut Vec<BFieldElement>) {
            let base = XFieldElement::new([
                stack.pop().unwrap(),
                stack.pop().unwrap(),
                stack.pop().unwrap(),
            ]);
            let exponent_log_2: u32 = stack.pop().unwrap().try_into().unwrap();
            let result = base.mod_pow_u32(2u32.pow(exponent_log_2));

            for elem in result.coefficients.into_iter().rev() {
                stack.push(elem);
            }
        }

        fn pseudorandom_initial_state(
            &self,
            seed: [u8; 32],
            bench_case: Option<crate::snippet_bencher::BenchmarkCase>,
        ) -> Vec<BFieldElement> {
            let mut rng: StdRng = SeedableRng::from_seed(seed);
            let exponent = match bench_case {
                Some(BenchmarkCase::CommonCase) => 20,
                Some(BenchmarkCase::WorstCase) => 31,
                None => rng.gen_range(0..32),
            };

            let base: XFieldElement = rng.gen();
            self.prepare_state(base, exponent)
        }

        fn corner_case_initial_states(&self) -> Vec<Vec<BFieldElement>> {
            let bfe_14 = BFieldElement::new(14);
            let an_xfe = XFieldElement::new([bfe_14, bfe_14, bfe_14]);
            (0..=5)
                .chain([30, 31])
                .map(|log_2_exp| self.prepare_state(an_xfe, log_2_exp))
                .collect_vec()
        }
    }

    impl ToThePowerOfPowerOf2 {
        fn prepare_state(&self, base: XFieldElement, log_2_exp: u32) -> Vec<BFieldElement> {
            let base = base.coefficients.into_iter().rev().collect();
            [
                self.init_stack_for_isolated_run(),
                vec![BFieldElement::new(log_2_exp as u64)],
                base,
            ]
            .concat()
        }
    }

    #[test]
    fn to_the_power_of_power_of_2_pbt() {
        ShadowedClosure::new(ToThePowerOfPowerOf2).test()
    }

    #[test]
    fn compare_to_generic_pow_u32() {
        let base: XFieldElement = random();
        for log_2_exponent in 0..32 {
            let init_stack_pow_pow = [
                ToThePowerOfPowerOf2.init_stack_for_isolated_run(),
                vec![BFieldElement::new(log_2_exponent)],
                base.coefficients.into_iter().rev().collect_vec(),
            ]
            .concat();
            let final_state_pow_pow = test_rust_equivalence_given_complete_state(
                &ShadowedClosure::new(ToThePowerOfPowerOf2),
                &init_stack_pow_pow,
                &[],
                &NonDeterminism::default(),
                &None,
                None,
            );

            // Run snippet for generic pow
            let init_stack_to_generic = [
                XfeModPowU32Generic.init_stack_for_isolated_run(),
                vec![BFieldElement::new(
                    2u64.pow(log_2_exponent.try_into().unwrap()),
                )],
                base.coefficients.into_iter().rev().collect_vec(),
            ]
            .concat();
            let final_state_from_generic = test_rust_equivalence_given_complete_state(
                &ShadowedClosure::new(XfeModPowU32Generic),
                &init_stack_to_generic,
                &[],
                &NonDeterminism::default(),
                &None,
                None,
            );

            // Assert that height agrees, and the top-3 elements agree
            assert_eq!(
                final_state_from_generic.op_stack.stack.len(),
                final_state_pow_pow.op_stack.stack.len()
            );
            assert_eq!(
                final_state_from_generic.op_stack.stack[16..=18],
                final_state_pow_pow.op_stack.stack[16..=18],
            );
        }
    }
}

#[cfg(test)]
mod benches {
    use super::*;
    use crate::traits::closure::ShadowedClosure;
    use crate::traits::rust_shadow::RustShadow;

    #[test]
    fn xfe_mod_pow_benchmark() {
        ShadowedClosure::new(ToThePowerOfPowerOf2).bench();
    }
}
tasm_lib/arithmetic/xfe/to_the_power_of_power_of_2.rs

tasm_lib/arithmetic/xfe/
to_the_power_of_power_of_2.rs
