rns-engine 0.4.0rc1

Exact RNS engine with session/cache API.

rns_engine

Exact 4-rail integer arithmetic via a Residue Number System (RNS), with AVX2 and optional OpenMP acceleration.

No floating point. No approximation. Exact results modulo the engine's dynamic range.

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What it does

Standard Python integers are exact but slow. NumPy arrays are fast, but fixed-width integer arithmetic can overflow and float-based pipelines drift. rns_engine gives you exact modular arithmetic within a fixed dynamic range by decomposing values across four coprime rails:

• 127
• 8191
• 65536
• 524287

Arithmetic is performed independently on each rail, then reconstructed with Garner-style CRT.

Dynamic range: [0, 35,742,890,181,197,824)

127 × 8191 × 65536 × 524287 = 35,742,890,181,197,824

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Install

pip install rns_engine

AVX2 note

HAS_AVX2 is a build-time property of the compiled extension, not runtime CPU detection. On supported x86_64 builds, the core can use AVX2 acceleration.

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Quick start

import numpy as np
import rns_engine as rns

a = np.array([123456789, 999999999], dtype=np.uint64)
b = np.array([987654321, 111111111], dtype=np.uint64)

ea = rns.encode(a)
eb = rns.encode(b)

out_add = rns.decode(*rns.add(*ea, *eb))
out_mul = rns.decode(*rns.mul(*ea, *eb))

# Chain multiple exact operations in residue space, decode once at the end
s1 = rns.add(*ea, *eb)
s2 = rns.mul(*s1, *eb)
s3 = rns.sub(*s2, *ea)
out = rns.decode(*s3)

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Session quick start

import numpy as np
import rns_engine as rns

s = rns.Session(cache_capacity=32)
x = np.array([1, 2, 3, 4], dtype=np.uint64)

# Cache-aware encode
ex = s.encode(x)

# Chain exact ops without decoding between steps
res = s.mul(s.add(ex, ex), ex)
out = s.decode(res)

# Single exact affine step
one = s.one_shot_affine(x, multiplier=1_000_003, addend=7)

# Repeated exact affine loop: stay in residue space, decode once
hot = s.hot_loop_affine(x, multiplier=1_000_003, addend=7, iterations=1000)

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Core API

Encoded rail API

• rns.encode(x) → (r0, r1, r2, r3)
• rns.decode(r0, r1, r2, r3) → uint64[]
• rns.add(*ea, *eb)
• rns.sub(*ea, *eb)
• rns.mul(*ea, *eb)
• rns.div_(*ea, *eb)
• rns.fma(*ea, *eb, *ec)
• rns.op(*ea, *eb, code) where 0=add 1=mul 2=sub 3=div

Scalar-broadcast encoded API

These avoid materializing full constant arrays in Python:

• rns.mul_u64(*ea, multiplier)
• rns.fma_u64(*ea, multiplier, addend)
• rns.affine_repeat_u64(*ea, multiplier, addend, iterations)

Raw fused uint64 API

These perform encode → exact op → decode in one native call:

• rns.add_u64_io(x, addend)
• rns.sub_u64_io(x, subtrahend)
• rns.mul_u64_io(x, multiplier)
• rns.fma_u64_io(x, multiplier, addend)
• rns.affine_repeat_u64_io(x, multiplier, addend, iterations)

OpenMP variants:

• rns.add_u64_io_omp(...)
• rns.sub_u64_io_omp(...)
• rns.mul_u64_io_omp(...)
• rns.fma_u64_io_omp(...)
• rns.affine_repeat_u64_io_omp(...)

Auto-dispatch variants:

• rns.add_u64_auto(...)
• rns.sub_u64_auto(...)
• rns.mul_u64_auto(...)
• rns.fma_u64_auto(...)
• rns.affine_repeat_u64_auto(...)

High-level API

• rns.Session
• rns.SessionCache
• rns.EncodedArray

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Division constraint

Division requires the divisor to be invertible on all four rails:

• b % 127 != 0
• b % 8191 != 0
• b must be odd (for mod 65536)
• b % 524287 != 0

A safe sanitizer looks like this:

import numpy as np
import rns_engine as rns

M = int(rns.M)

def make_invertible_divisor(b):
    b = np.asarray(b, dtype=np.uint64) % np.uint64(M)
    b = np.where((b & np.uint64(1)) == 0, b + np.uint64(1), b)

    bad = (
        (b % np.uint64(127) == 0)
        | (b % np.uint64(8191) == 0)
        | (b % np.uint64(524287) == 0)
        | ((b & np.uint64(1)) == 0)
    )

    while np.any(bad):
        b = np.where(bad, (b + np.uint64(2)) % np.uint64(M), b)
        bad = (
            (b % np.uint64(127) == 0)
            | (b % np.uint64(8191) == 0)
            | (b % np.uint64(524287) == 0)
            | ((b & np.uint64(1)) == 0)
        )

    return b.astype(np.uint64)

---

Data model

• input arrays to encode(...) are treated as uint64
• values outside [0, M) are reduced mod M during encode
• rails are returned as:
  • r0: uint16
  • r1: uint16
  • r2: uint16
  • r3: uint32
• high-level EncodedArray objects store four read-only rails

---

Performance

Verified benchmark

Verified on Google Colab Linux x86_64, with:

• AVX2 = True
• omp_num_procs = 2
• omp_max_threads = 2

Workloads were run against the installed wheel, not just an editable import.

Median throughput over 5 runs on 1,000,000 uint64 values:

Fused single-step affine

Workload: fma_u64_io(x, 1_000_003, 7)

• fused fma_u64_io: 47.8 million values/sec
• fma_u64_io_omp (1 thread): 80.7 million values/sec
• fma_u64_io_omp (2 threads): 84.6 million values/sec

Repeated affine loop

Workload: affine_repeat_u64_io(x, 1_000_003, 7, iterations=1000)

• affine_repeat_u64_io: 61.19 billion ops/sec
• affine_repeat_u64_io_omp (1 thread): 82.80 billion ops/sec
• affine_repeat_u64_io_omp (2 threads): 94.86 billion ops/sec

Verification status

• correctness sanity checks passed
• built wheel installed and executed successfully
• full test suite passed: 49 / 49

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Why RNS?

In a Residue Number System, addition and multiplication happen independently on each rail. There is no cross-rail carry propagation. That makes RNS attractive for:

• exact modular arithmetic within a fixed dynamic range
• SIMD-friendly kernels
• repeated arithmetic pipelines where decode can be delayed
• parallel execution

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How it works

Encode

x -> (x mod 127, x mod 8191, x mod 65536, x mod 524287)

Operate

Each rail is processed independently.

Decode

Garner-style CRT reconstruction combines the four residues back into a uint64 value modulo M.

For the Mersenne moduli (127 = 2^7 - 1, 8191 = 2^13 - 1, 524287 = 2^19 - 1), the core uses fold-based reduction instead of general division.

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Building from source

git clone https://github.com/playfularchitect/rns_engine.git
cd rns_engine
pip install -e .
pytest tests/ -v

Requirements:

• Python 3.10+
• C++17 compiler
• NumPy
• pybind11

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Introspection

import rns_engine as rns

rns.info()

rns.M
rns.M0
rns.M1
rns.M2
rns.M3
rns.HAS_AVX2

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Current release

v0.4.0rc1

• 4-rail engine (127 × 8191 × 65536 × 524287)
• AVX2-accelerated encoded kernels
• fused fma(...)
• scalar-broadcast encoded APIs: mul_u64, fma_u64, affine_repeat_u64
• fused raw uint64 APIs: *_u64_io
• OpenMP fused raw APIs: *_u64_io_omp
• auto-dispatch raw APIs: *_u64_auto
• high-level Session, SessionCache, and EncodedArray

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License

AGPL-3.0-only
Copyright 2026 Evan Wesley