High-performance DNA/RNA sequence encoding and decoding using SIMD instructions with automatic fallback to scalar implementations.

Table of Contents

• Table of Contents
• Features
• Installation
• IUPAC Nucleotide Codes
  • Standard Nucleotides
  • Two-Base Ambiguity Codes
  • Three-Base Ambiguity Codes
  • Wildcards and Gaps
  • Bit Rotation Property
• Usage
• Reverse Complement
  • IUPAC Ambiguity Code Complements
• Input Handling
• Integration
  • Working with seq_io
  • Working with noodles
  • Working with rust-bio
  • Zero-Copy Integration
• Platform Support
• Performance
• Testing
  • Unit Tests
  • Fuzz Testing
• Contributing
• Changelog
• Citation
• License

Features

• 4-bit encoding supporting all IUPAC nucleotide codes (16 standard + U for RNA)
• Bit-rotation-compatible encoding enabling efficient complement calculation
• SIMD-accelerated reverse complement operations
• SIMD acceleration on x86_64 (SSSE3) and ARM64 (NEON)
• Static lookup tables for branch-free encoding/decoding
• Prefetch hints for improved cache utilization on large sequences
• Automatic fallback to optimized scalar implementation
• Thread-safe pure functions with no global state
• 2:1 compression ratio compared to ASCII representation
• RNA support via U (Uracil) mapping to T

Installation

Add simdna to your Cargo.toml:

[dependencies]
simdna = "1.0.2"

Or install via cargo:

cargo add simdna

IUPAC Nucleotide Codes

simdna supports the complete IUPAC nucleotide alphabet with a bit-rotation-compatible encoding scheme. This encoding enables efficient complement calculation via a simple 2-bit rotation operation.

Standard Nucleotides

Code	Meaning	Value	Complement
A	Adenine	0x1	T (0x4)
C	Cytosine	0x2	G (0x8)
G	Guanine	0x8	C (0x2)
T	Thymine	0x4	A (0x1)
U	Uracil (RNA → T)	0x4	A (0x1)

Two-Base Ambiguity Codes

Code	Meaning	Value	Complement
R	A or G (purine)	0x9	Y (0x6)
Y	C or T (pyrimidine)	0x6	R (0x9)
S	G or C (strong)	0xA	S (0xA)
W	A or T (weak)	0x5	W (0x5)
K	G or T (keto)	0xC	M (0x3)
M	A or C (amino)	0x3	K (0xC)

Three-Base Ambiguity Codes

Code	Meaning	Value	Complement
B	C, G, or T (not A)	0xE	V (0xB)
D	A, G, or T (not C)	0xD	H (0x7)
H	A, C, or T (not G)	0x7	D (0xD)
V	A, C, or G (not T)	0xB	B (0xE)

Wildcards and Gaps

Code	Meaning	Value	Complement
N	Any base	0xF	N (0xF)
-	Gap / deletion	0x0	- (0x0)
.	Gap (alternative)	0x0	- (0x0)

Bit Rotation Property

The encoding is designed so that the complement of any nucleotide can be computed via a 2-bit rotation:

complement = ((bits << 2) | (bits >> 2)) & 0xF

This enables SIMD-accelerated reverse complement operations that are ~2x faster than lookup table approaches.

Usage

use simdna::dna_simd_encoder::{encode_dna_prefer_simd, decode_dna_prefer_simd};

// Encode a DNA sequence with IUPAC codes
let sequence = b"ACGTNRYSWKMBDHV-";
let encoded = encode_dna_prefer_simd(sequence);

// The encoded data is 2x smaller (2 nucleotides per byte)
assert_eq!(encoded.len(), sequence.len() / 2);

// Decode back to the original sequence
let decoded = decode_dna_prefer_simd(&encoded, sequence.len());
assert_eq!(decoded, sequence);

// RNA sequences work seamlessly (U maps to T)
let rna = b"ACGU";
let encoded_rna = encode_dna_prefer_simd(rna);
let decoded_rna = decode_dna_prefer_simd(&encoded_rna, rna.len());
assert_eq!(decoded_rna, b"ACGT"); // U decodes as T

Reverse Complement

simdna provides efficient SIMD-accelerated reverse complement operations for DNA/RNA sequences with consistent performance for both even and odd-length sequences:

use simdna::dna_simd_encoder::{reverse_complement, reverse_complement_encoded, encode_dna_prefer_simd};

// High-level API: ASCII in, ASCII out
let sequence = b"ACGT";
let rc = reverse_complement(sequence);
assert_eq!(rc, b"ACGT"); // ACGT is its own reverse complement

// Biological example
let forward = b"ATGCAACG";
let rc = reverse_complement(forward);
assert_eq!(rc, b"CGTTGCAT");

// Low-level API: operates directly on encoded data for maximum performance (~20 GiB/s)
let encoded = encode_dna_prefer_simd(b"ACGT");
let rc_encoded = reverse_complement_encoded(&encoded, 4);
// rc_encoded is the encoded form of "ACGT"

IUPAC Ambiguity Code Complements

Reverse complement correctly handles all IUPAC ambiguity codes:

use simdna::dna_simd_encoder::reverse_complement;

// R (purine: A|G) complements to Y (pyrimidine: C|T)
assert_eq!(reverse_complement(b"R"), b"Y");

// Self-complementary codes: S (G|C), W (A|T), N (any)
assert_eq!(reverse_complement(b"SWN"), b"NWS");

Input Handling

• Case insensitive: Both "ACGT" and "acgt" encode identically
• Invalid characters: Non-IUPAC characters (X, digits, etc.) encode as gap (0xF)
• Decoding: Always produces uppercase nucleotides

Integration

simdna focuses exclusively on high-performance encoding/decoding, making it composable with any FASTA/FASTQ parser or custom format. This keeps the library lightweight and lets you choose the tools that fit your workflow.

Working with seq_io

seq_io is a fast FASTA/FASTQ parser. simdna works directly with its borrowed sequence data:

use seq_io::fasta::Reader;
use simdna::dna_simd_encoder::encode_dna_prefer_simd;

let mut reader = Reader::from_path("genome.fasta")?;
while let Some(record) = reader.next() {
    let record = record?;
    // seq_io provides &[u8] directly - no allocation needed
    let encoded = encode_dna_prefer_simd(record.seq());
    // ... use encoded data
}

Working with noodles

noodles is a comprehensive bioinformatics I/O library:

use noodles::fasta;
use simdna::dna_simd_encoder::encode_dna_prefer_simd;

let mut reader = fasta::io::reader::Builder::default().build_from_path("genome.fasta")?;
for result in reader.records() {
    let record = result?;
    let encoded = encode_dna_prefer_simd(record.sequence().as_ref());
    // ... use encoded data
}

Working with rust-bio

rust-bio provides algorithms and data structures for bioinformatics:

use bio::io::fasta;
use simdna::dna_simd_encoder::encode_dna_prefer_simd;

let reader = fasta::Reader::from_file("genome.fasta")?;
for result in reader.records() {
    let record = result?;
    let encoded = encode_dna_prefer_simd(record.seq());
    // ... use encoded data
}

Zero-Copy Integration

simdna accepts &[u8] slices, enabling zero-copy integration with parsers. Avoid unnecessary allocations:

// ✓ Good: Work directly with borrowed data
let encoded = encode_dna_prefer_simd(record.seq());

// ✗ Avoid: Unnecessary allocation
let owned: Vec<u8> = record.seq().to_vec();
let encoded = encode_dna_prefer_simd(&owned);

Most FASTA/FASTQ parsers provide sequence data as &[u8] or types that implement AsRef<[u8]>, which work directly with simdna's API.

Platform Support

Platform	SIMD	Fallback
x86_64	SSSE3	Scalar
ARM64	NEON	Scalar
Other	-	Scalar

Performance

simdna employs multiple optimization strategies:

• Static Lookup Tables: Pre-computed encode/decode tables eliminate branch mispredictions
• SIMD Processing: Handles 32 nucleotides per iteration (two 16-byte chunks) with prefetching
• Direct Case Handling: LUT handles case-insensitivity without uppercase conversion overhead
• Optimized Scalar Path: Remainder processing uses 4-at-a-time scalar encoding
• SIMD Reverse Complement: Up to ~20 GiB/s throughput on encoded data, 4-6x faster than scalar
• Consistent Performance: Both even and odd-length sequences achieve similar throughput
• 2:1 Compression: 4 bits per nucleotide vs 8 bits ASCII

_{Benchmarks obtained on a Mac Studio with 32GB RAM and Apple M1 Max chip running macOS Tahoe 26.1 using the Criterion.rs statistics-driven micro-benchmarking library.}

Testing

simdna employs a comprehensive testing strategy to ensure correctness and robustness:

Unit Tests

Run the standard test suite with:

cargo test

The unit tests cover:

• Encoding and decoding of all IUPAC nucleotide codes
• Case insensitivity handling
• Invalid character handling
• Odd and even length sequences
• Empty input edge cases
• SIMD and scalar implementation equivalence

Fuzz Testing

simdna uses cargo-fuzz for property-based fuzz testing to discover edge cases and potential bugs. The following fuzz targets are available:

Target	Description
roundtrip	Verifies encode→decode produces consistent output
valid_iupac	Tests encoding of valid IUPAC sequences
decode_robust	Tests decoder resilience to arbitrary byte sequences
boundaries	Tests sequence length boundary conditions
simd_scalar_equivalence	Verifies SIMD and scalar implementations produce identical results
bit_rotation	Verifies bit rotation complement properties (involution, consistency)
reverse_complement	Tests reverse complement correctness (double-rc = original)

Run fuzz tests with:

cargo +nightly fuzz run <target> -- -max_total_time=60

Contributing

Contributions are welcome! Please see CONTRIBUTING.md for guidelines on bug reports and feature requests.

Changelog

See CHANGELOG.md for a history of changes to this project.

Citation

If you use simdna in your research, please cite it using the metadata in CITATION.cff. GitHub can also generate citation information directly from the repository page.

License

This project is licensed under the MIT License - see LICENSE for details.