Module engine

Low-level building blocks for Reed-Solomon encoding/decoding.

This is an advanced module which is not needed for simple usage or basic usage.

This module is relevant if you want to

• use rate module and need an Engine to use with it.
• create your own Engine.
• understand/benchmark/test at low level.

Engines

An Engine is an implementation of basic low-level algorithms needed for Reed-Solomon encoding/decoding.

• Naive
  • Simple reference implementation.
• NoSimd
  • Basic optimized engine without SIMD so that it works on all CPUs.
• DefaultEngine
  • Default engine which is used when no specific engine is given.
  • Currently just alias to NoSimd.

Benchmarks

• These benchmarks are from cargo bench engine with 3.4 GHz i5-3570K (Ivy Bridge, 3rd gen.).
• Shards are 1024 bytes.

Benchmark	Shards	ns Naive	ns NoSimd
xor	1 * 2	60	32
mul	1	1 260	860
xor_within	128 * 2	5 870	5 780
formal_derivative	128	21 300	15 800
FFT	128	764 000	545 000
IFFT	128	780 000	546 000
FWHT	-	898 000	622 000

Modules

• tables
  Lookup-tables used by Engine:s.

Structs

• Naive
  Simple reference implementation of Engine.
• NoSimd
  Optimized Engine without SIMD.
• ShardsRefMut
  Mutable reference to shard array implemented as flat byte array.

Constants

• CANTOR_BASIS
  TODO
• GF_BITS
  Size of Galois field element GfElement in bits.
• GF_MODULUS
  GF_ORDER - 1
• GF_ORDER
  Galois field order, i.e. number of elements.
• GF_POLYNOMIAL
  Galois field polynomial.

Traits

• Engine
  Implementation of basic low-level algorithms needed for Reed-Solomon encoding/decoding.

Functions

• add_mod
  Some kind of addition.
• checked_next_multiple_of
  Returns smallest value that is greater than or equal to a and multiple of b, or None if b is zero or operation would overflow.
• sub_mod
  Some kind of subtraction.

Type Aliases

• DefaultEngine
  Default Engine, currently just alias to NoSimd.
• GfElement
  Galois field element.