commonware_cryptography/reed_solomon/rate/

rate_high.rs

use crate::reed_solomon::{
    engine::{self, Engine, GF_MODULUS, GF_ORDER, SHARD_CHUNK_BYTES},
    rate::{DecoderWork, EncoderWork, Rate, RateDecoder, RateEncoder},
    DecoderResult, EncoderResult, Error,
};
use core::marker::PhantomData;

// ======================================================================
// HighRate - PUBLIC

/// Reed-Solomon encoder/decoder generator using only high rate.
pub struct HighRate<E: Engine>(PhantomData<E>);

impl<E: Engine> Rate<E> for HighRate<E> {
    type RateEncoder = HighRateEncoder<E>;
    type RateDecoder = HighRateDecoder<E>;

    fn supports(original_count: usize, recovery_count: usize) -> bool {
        original_count > 0
            && recovery_count > 0
            && original_count < GF_ORDER
            && recovery_count < GF_ORDER
            && recovery_count.next_power_of_two() + original_count <= GF_ORDER
    }
}

// ======================================================================
// HighRateEncoder - PUBLIC

/// Reed-Solomon encoder using only high rate.
pub struct HighRateEncoder<E: Engine> {
    engine: E,
    work: EncoderWork,
}

impl<E: Engine> RateEncoder<E> for HighRateEncoder<E> {
    type Rate = HighRate<E>;

    fn add_original_shard<T: AsRef<[u8]>>(&mut self, original_shard: T) -> Result<(), Error> {
        self.work.add_original_shard(original_shard)
    }

    fn encode(&mut self) -> Result<EncoderResult<'_>, Error> {
        let (mut work, original_count, recovery_count) = self.work.encode_begin()?;
        let chunk_size = recovery_count.next_power_of_two();
        let engine = &self.engine;

        // FIRST CHUNK

        let first_count = core::cmp::min(original_count, chunk_size);

        work.zero(first_count..chunk_size);
        engine::ifft_skew_end(engine, &mut work, 0, chunk_size, first_count);

        if original_count > chunk_size {
            // FULL CHUNKS

            let mut chunk_start = chunk_size;
            while chunk_start + chunk_size <= original_count {
                engine::ifft_skew_end(engine, &mut work, chunk_start, chunk_size, chunk_size);
                engine::xor_within(&mut work, 0, chunk_start, chunk_size);
                chunk_start += chunk_size;
            }

            // FINAL PARTIAL CHUNK

            let last_count = original_count % chunk_size;
            if last_count > 0 {
                work.zero(chunk_start + last_count..);
                engine::ifft_skew_end(engine, &mut work, chunk_start, chunk_size, last_count);
                engine::xor_within(&mut work, 0, chunk_start, chunk_size);
            }
        }

        // FFT

        engine.fft(&mut work, 0, chunk_size, recovery_count, 0);

        // UNDO LAST CHUNK ENCODING

        self.work.undo_last_chunk_encoding();

        // DONE

        Ok(EncoderResult::new(&mut self.work))
    }

    fn into_parts(self) -> (E, EncoderWork) {
        (self.engine, self.work)
    }

    fn new(
        original_count: usize,
        recovery_count: usize,
        shard_bytes: usize,
        engine: E,
        work: Option<EncoderWork>,
    ) -> Result<Self, Error> {
        let mut work = work.unwrap_or_default();
        Self::reset_work(original_count, recovery_count, shard_bytes, &mut work)?;
        Ok(Self { engine, work })
    }

    fn reset(
        &mut self,
        original_count: usize,
        recovery_count: usize,
        shard_bytes: usize,
    ) -> Result<(), Error> {
        Self::reset_work(original_count, recovery_count, shard_bytes, &mut self.work)
    }
}

// ======================================================================
// HighRateEncoder - PRIVATE

impl<E: Engine> HighRateEncoder<E> {
    fn reset_work(
        original_count: usize,
        recovery_count: usize,
        shard_bytes: usize,
        work: &mut EncoderWork,
    ) -> Result<(), Error> {
        Self::validate(original_count, recovery_count, shard_bytes)?;
        work.reset(
            original_count,
            recovery_count,
            shard_bytes,
            Self::work_count(original_count, recovery_count),
        );
        Ok(())
    }

    fn work_count(original_count: usize, recovery_count: usize) -> usize {
        assert!(Self::supports(original_count, recovery_count));

        let chunk_size = recovery_count.next_power_of_two();

        original_count.next_multiple_of(chunk_size)
    }
}

// ======================================================================
// HighRateDecoder - PUBLIC

/// Reed-Solomon decoder using only high rate.
pub struct HighRateDecoder<E: Engine> {
    engine: E,
    work: DecoderWork,
}

impl<E: Engine> RateDecoder<E> for HighRateDecoder<E> {
    type Rate = HighRate<E>;

    fn add_original_shard<T: AsRef<[u8]>>(
        &mut self,
        index: usize,
        original_shard: T,
    ) -> Result<(), Error> {
        self.work.add_original_shard(index, original_shard)
    }

    fn add_recovery_shard<T: AsRef<[u8]>>(
        &mut self,
        index: usize,
        recovery_shard: T,
    ) -> Result<(), Error> {
        self.work.add_recovery_shard(index, recovery_shard)
    }

    fn decode(&mut self, compute_recovery: bool) -> Result<Option<DecoderResult<'_>>, Error> {
        let Some((mut work, original_count, recovery_count, received)) =
            self.work.decode_begin()?
        else {
            // Every original was provided: nothing to reconstruct. Clear the received state and
            // report nothing.
            self.work.reset_received();
            return Ok(None);
        };

        let chunk_size = recovery_count.next_power_of_two();
        let original_end = chunk_size + original_count;
        let work_count = work.len();

        // ERASURE LOCATIONS

        let mut erasures = [0; GF_ORDER];

        for i in 0..recovery_count {
            if !received[i] {
                erasures[i] = 1;
            }
        }

        erasures[recovery_count..chunk_size].fill(1);

        for i in chunk_size..original_end {
            if !received[i] {
                erasures[i] = 1;
            }
        }

        // EVALUATE POLYNOMIAL

        E::eval_poly(&mut erasures, original_end);

        // MULTIPLY SHARDS

        // work[               .. recovery_count] = recovery * erasures
        // work[recovery_count .. chunk_size    ] = 0
        // work[chunk_size     .. original_end  ] = original * erasures
        // work[original_end   ..               ] = 0

        for i in 0..recovery_count {
            if received[i] {
                self.engine.mul(&mut work[i], erasures[i]);
            } else {
                work[i].fill([0; SHARD_CHUNK_BYTES]);
            }
        }

        work.zero(recovery_count..chunk_size);

        for i in chunk_size..original_end {
            if received[i] {
                self.engine.mul(&mut work[i], erasures[i]);
            } else {
                work[i].fill([0; SHARD_CHUNK_BYTES]);
            }
        }

        work.zero(original_end..);

        // IFFT / FORMAL DERIVATIVE / FFT

        self.engine.ifft(&mut work, 0, work_count, original_end, 0);
        engine::formal_derivative(&mut work);
        self.engine.fft(&mut work, 0, work_count, original_end, 0);

        // REVEAL ERASURES

        for i in chunk_size..original_end {
            if !received[i] {
                self.engine.mul(&mut work[i], GF_MODULUS - erasures[i]);
            }
        }

        // REVEAL ERASURES (RECOVERY)
        //
        // Only when the caller passed `compute_recovery = true` to `decode`. Recovery shards
        // live at `work[0..recovery_count]`. Un-scale the missing ones by the inverse locator so
        // they hold the canonical recovery values, mirroring the original reveal above. This lets
        // `DecoderResult::recovery` return them without a separate re-encode.

        if compute_recovery {
            for i in 0..recovery_count {
                if !received[i] {
                    self.engine.mul(&mut work[i], GF_MODULUS - erasures[i]);
                }
            }
        }

        // UNDO LAST CHUNK ENCODING

        self.work.undo_last_chunk_encoding();
        if compute_recovery {
            self.work.undo_last_chunk_encoding_recovery();
        }

        // DONE

        Ok(Some(DecoderResult::new(&mut self.work)))
    }

    fn into_parts(self) -> (E, DecoderWork) {
        (self.engine, self.work)
    }

    fn new(
        original_count: usize,
        recovery_count: usize,
        shard_bytes: usize,
        engine: E,
        work: Option<DecoderWork>,
    ) -> Result<Self, Error> {
        let mut work = work.unwrap_or_default();
        Self::reset_work(original_count, recovery_count, shard_bytes, &mut work)?;
        Ok(Self { engine, work })
    }

    fn reset(
        &mut self,
        original_count: usize,
        recovery_count: usize,
        shard_bytes: usize,
    ) -> Result<(), Error> {
        Self::reset_work(original_count, recovery_count, shard_bytes, &mut self.work)
    }
}

// ======================================================================
// HighRateDecoder - PRIVATE

impl<E: Engine> HighRateDecoder<E> {
    fn reset_work(
        original_count: usize,
        recovery_count: usize,
        shard_bytes: usize,
        work: &mut DecoderWork,
    ) -> Result<(), Error> {
        Self::validate(original_count, recovery_count, shard_bytes)?;

        // work[..recovery_count     ]  =  recovery
        // work[recovery_count_pow2..]  =  original
        work.reset(
            original_count,
            recovery_count,
            shard_bytes,
            recovery_count.next_power_of_two(),
            0,
            Self::work_count(original_count, recovery_count),
        );

        Ok(())
    }

    fn work_count(original_count: usize, recovery_count: usize) -> usize {
        assert!(Self::supports(original_count, recovery_count));

        (recovery_count.next_power_of_two() + original_count).next_power_of_two()
    }
}

// ======================================================================
// TESTS

#[cfg(test)]
mod tests {
    use super::*;
    use crate::reed_solomon::test_util;

    // ============================================================
    // ROUNDTRIPS - SINGLE ROUND

    #[test]
    fn roundtrip_all_originals_missing() {
        roundtrip_single!(
            HighRate,
            3,
            3,
            1024,
            test_util::EITHER_3_3,
            &[],
            &[test_util::range(0, 3)],
            133,
        );
    }

    #[test]
    fn roundtrip_no_originals_missing() {
        roundtrip_single!(
            HighRate,
            3,
            2,
            1024,
            test_util::HIGH_3_2,
            &[test_util::range(0, 3)],
            &[],
            132
        );
    }

    #[test]
    fn roundtrips_tiny() {
        for (original_count, recovery_count, seed, recovery_hash) in test_util::HIGH_TINY {
            roundtrip_single!(
                HighRate,
                *original_count,
                *recovery_count,
                1024,
                recovery_hash,
                &[test_util::range(*recovery_count, *original_count)],
                &[test_util::range(
                    0,
                    core::cmp::min(*original_count, *recovery_count)
                )],
                *seed,
            );
        }
    }

    #[test]
    #[ignore]
    fn roundtrip_3000_30000() {
        roundtrip_single!(
            HighRate,
            3000,
            30000,
            crate::reed_solomon::SHARD_CHUNK_BYTES,
            test_util::HIGH_3000_30000_14,
            &[],
            &[test_util::range(0, 3000)],
            14,
        );
    }

    #[test]
    #[ignore]
    fn roundtrip_32768_32768() {
        roundtrip_single!(
            HighRate,
            32768,
            32768,
            crate::reed_solomon::SHARD_CHUNK_BYTES,
            test_util::EITHER_32768_32768_11,
            &[],
            &[test_util::range(0, 32768)],
            11,
        );
    }

    #[test]
    #[ignore]
    fn roundtrip_60000_3000() {
        roundtrip_single!(
            HighRate,
            60000,
            3000,
            crate::reed_solomon::SHARD_CHUNK_BYTES,
            test_util::HIGH_60000_3000_12,
            &[test_util::range(3000, 60000)],
            &[test_util::range(0, 3000)],
            12,
        );
    }

    #[test]
    fn roundtrip_34000_2000_shard_size_8() {
        roundtrip_single!(
            HighRate,
            34000,
            2000,
            8,
            test_util::HIGH_34000_2000_123_8,
            &[test_util::range(0, 32000)],
            &[test_util::range(0, 2000)],
            123
        );
    }

    // ============================================================
    // ROUNDTRIPS - TWO ROUNDS

    #[test]
    fn two_rounds_implicit_reset() {
        roundtrip_two_rounds!(
            HighRate,
            false,
            (
                3,
                2,
                1024,
                test_util::HIGH_3_2,
                &[test_util::index(1)],
                &[test_util::index(0), test_util::index(1)],
                132
            ),
            (
                3,
                2,
                1024,
                test_util::HIGH_3_2_232,
                &[test_util::index(0)],
                &[test_util::index(0), test_util::index(1)],
                232
            ),
        );
    }

    #[test]
    fn two_rounds_explicit_reset() {
        roundtrip_two_rounds!(
            HighRate,
            true,
            (
                3,
                2,
                1024,
                test_util::HIGH_3_2,
                &[test_util::index(1)],
                &[test_util::index(0), test_util::index(1)],
                132
            ),
            (
                5,
                2,
                1024,
                test_util::HIGH_5_2,
                &[
                    test_util::index(0),
                    test_util::index(2),
                    test_util::index(4)
                ],
                &[test_util::index(0), test_util::index(1)],
                152
            ),
        );
    }

    // ============================================================
    // HighRate

    mod high_rate {
        use crate::reed_solomon::{
            engine::NoSimd,
            rate::{HighRate, Rate},
            Error, SHARD_CHUNK_BYTES,
        };

        #[test]
        fn decoder() {
            assert_eq!(
                HighRate::<NoSimd>::decoder(4096, 61440, SHARD_CHUNK_BYTES, NoSimd::new(), None)
                    .err(),
                Some(Error::UnsupportedShardCount {
                    original_count: 4096,
                    recovery_count: 61440,
                })
            );

            assert!(HighRate::<NoSimd>::decoder(
                61440,
                4096,
                SHARD_CHUNK_BYTES,
                NoSimd::new(),
                None
            )
            .is_ok());
        }

        #[test]
        fn encoder() {
            assert_eq!(
                HighRate::<NoSimd>::encoder(4096, 61440, SHARD_CHUNK_BYTES, NoSimd::new(), None)
                    .err(),
                Some(Error::UnsupportedShardCount {
                    original_count: 4096,
                    recovery_count: 61440,
                })
            );

            assert!(HighRate::<NoSimd>::encoder(
                61440,
                4096,
                SHARD_CHUNK_BYTES,
                NoSimd::new(),
                None
            )
            .is_ok());
        }

        #[test]
        fn supports() {
            assert!(!HighRate::<NoSimd>::supports(0, 1));
            assert!(!HighRate::<NoSimd>::supports(1, 0));

            assert!(!HighRate::<NoSimd>::supports(4096, 61440));

            assert!(HighRate::<NoSimd>::supports(61440, 4096));
            assert!(!HighRate::<NoSimd>::supports(61440, 4097));
            assert!(!HighRate::<NoSimd>::supports(61441, 4096));

            assert!(!HighRate::<NoSimd>::supports(usize::MAX, usize::MAX));
        }

        #[test]
        fn validate() {
            assert_eq!(
                HighRate::<NoSimd>::validate(1, 1, 123).err(),
                Some(Error::InvalidShardSize { shard_bytes: 123 })
            );

            assert_eq!(
                HighRate::<NoSimd>::validate(4096, 61440, SHARD_CHUNK_BYTES).err(),
                Some(Error::UnsupportedShardCount {
                    original_count: 4096,
                    recovery_count: 61440,
                })
            );

            assert!(HighRate::<NoSimd>::validate(61440, 4096, SHARD_CHUNK_BYTES).is_ok());
        }
    }

    // ============================================================
    // HighRateEncoder

    mod high_rate_encoder {
        use crate::reed_solomon::{
            engine::NoSimd,
            rate::{HighRateEncoder, RateEncoder},
            Error, SHARD_CHUNK_BYTES,
        };

        // ==================================================
        // ERRORS

        test_rate_encoder_errors! {HighRateEncoder}

        // ==================================================
        // supports

        #[test]
        fn supports() {
            assert!(!HighRateEncoder::<NoSimd>::supports(4096, 61440));
            assert!(HighRateEncoder::<NoSimd>::supports(61440, 4096));
        }

        // ==================================================
        // validate

        #[test]
        fn validate() {
            assert_eq!(
                HighRateEncoder::<NoSimd>::validate(1, 1, 123).err(),
                Some(Error::InvalidShardSize { shard_bytes: 123 })
            );

            assert_eq!(
                HighRateEncoder::<NoSimd>::validate(4096, 61440, SHARD_CHUNK_BYTES).err(),
                Some(Error::UnsupportedShardCount {
                    original_count: 4096,
                    recovery_count: 61440,
                })
            );

            assert!(HighRateEncoder::<NoSimd>::validate(61440, 4096, SHARD_CHUNK_BYTES).is_ok());
        }

        // ==================================================
        // work_count

        #[test]
        fn work_count() {
            assert_eq!(HighRateEncoder::<NoSimd>::work_count(1, 1), 1);
            assert_eq!(HighRateEncoder::<NoSimd>::work_count(4096, 1024), 4096);
            assert_eq!(HighRateEncoder::<NoSimd>::work_count(4097, 1024), 5120);
            assert_eq!(HighRateEncoder::<NoSimd>::work_count(4097, 1025), 6144);
            assert_eq!(HighRateEncoder::<NoSimd>::work_count(32768, 32768), 32768);
        }
    }

    // ============================================================
    // HighRateDecoder

    mod high_rate_decoder {
        use crate::reed_solomon::{
            engine::NoSimd,
            rate::{HighRateDecoder, RateDecoder},
            Error, SHARD_CHUNK_BYTES,
        };

        // ==================================================
        // ERRORS

        test_rate_decoder_errors! {HighRateDecoder}

        // ==================================================
        // supports

        #[test]
        fn supports() {
            assert!(!HighRateDecoder::<NoSimd>::supports(4096, 61440));
            assert!(HighRateDecoder::<NoSimd>::supports(61440, 4096));
        }

        // ==================================================
        // validate

        #[test]
        fn validate() {
            assert_eq!(
                HighRateDecoder::<NoSimd>::validate(1, 1, 123).err(),
                Some(Error::InvalidShardSize { shard_bytes: 123 })
            );

            assert_eq!(
                HighRateDecoder::<NoSimd>::validate(4096, 61440, SHARD_CHUNK_BYTES).err(),
                Some(Error::UnsupportedShardCount {
                    original_count: 4096,
                    recovery_count: 61440,
                })
            );

            assert!(HighRateDecoder::<NoSimd>::validate(61440, 4096, SHARD_CHUNK_BYTES).is_ok());
        }

        // ==================================================
        // work_count

        #[test]
        fn work_count() {
            assert_eq!(HighRateDecoder::<NoSimd>::work_count(1, 1), 2);
            assert_eq!(HighRateDecoder::<NoSimd>::work_count(2048, 1025), 4096);
            assert_eq!(HighRateDecoder::<NoSimd>::work_count(2049, 1025), 8192);
            assert_eq!(HighRateDecoder::<NoSimd>::work_count(3072, 1024), 4096);
            assert_eq!(HighRateDecoder::<NoSimd>::work_count(3073, 1024), 8192);
            assert_eq!(HighRateDecoder::<NoSimd>::work_count(32768, 32768), 65536);
        }
    }
}