#### README.nd

This is revision 2.0 of Jerasure. This is pretty much Jerasure 1.2 without the

original Galois Field backend. Version 2.0 links directly to GF-Complete.

External Documentation:

See technical report CS-08-627 for a description of the main interfaces (Version 1.2)

See http://web.eecs.utk.edu/~plank/plank/papers/CS-13-703.html for information

on GF-Complete and the tarball needed to install it.

Custom usgae of GF-Complete is explained in this file (see below).

NOTE: You must have GF-Complete installed in order to use Jerasure 2.0.

There are two directories:

The home directory contains the jerasure code.

The Examples directory contains the example programs.

The makefile assumes that Examples is a subdirectory of the home directory.

Inclusion of GF-Complete:

As long as GF-Complete is installed, Jerasure 2.0 can be used just as previous

versions. There is no need to define custom Galois Fields. Jerasure will

determine the default field to use, if one is not specified.

If you would like to explore a using a different Galois Field implementation,

you can dynamically set the backend GF for a given word-size (w).

The new galois.[ch] exports the following functions to be used by applications

for dynamically setting the backend GF:

1.) galois_change_technique

Function signature:

void galois_change_technique(gf_t *gf, int w);

This function will take a pointer to a Galois field structure and set it as the

current backend for all operations in GF(2^w). Note that you must specify 'w'

here, since the internal GF structure is mostly opaque to Jerasure. Be sure to

change the technique with the correct structure and word-size.

There are a few ways to get a pointer to a gf_t structure: via GF-Complete or

using the helper functions provided by Jerasure: galois_init_field and

galois_init_composite_field.

GF-Complete exposes create_gf_from_argv, gf_init_easy and gf_init_hard. See

the GF-Complete documentation for more detail on how to use those functions.

You can definitely create more complicated fields with the GF-Complete

initialization functions, but the two helper functions provided by Jerasure

(galois_init_field and galois_init_composite_field) can be used to create most

of the supported Galois Fields.

2.) galois_init_field

Function signature:

gf_t* galois_init_field(int w,

int mult_type,

int region_type,

int divide_type,

uint64_t prim_poly,

int arg1,

int arg2);

This is a helper function that will initialize a Galois field. See the GF-Complete

documentation for more info on what the arguments mean. Here is a brief description

of the arguments:

mult_type can be any *one* of the following:

GF_MULT_DEFAULT

GF_MULT_SHIFT

GF_MULT_CARRY_FREE

GF_MULT_GROUP

GF_MULT_BYTWO_p

GF_MULT_BYTWO_b

GF_MULT_TABLE

GF_MULT_LOG_TABLE

GF_MULT_LOG_ZERO

GF_MULT_LOG_ZERO_EXT

GF_MULT_SPLIT_TABLE

region_type can be a combination of the following (some combinations will not

be valid):

GF_REGION_DEFAULT

GF_REGION_DOUBLE_TABLE

GF_REGION_QUAD_TABLE

GF_REGION_LAZY

GF_REGION_SSE

GF_REGION_NOSSE

GF_REGION_ALTMAP

GF_REGION_CAUCHY

divide_type can be one of the following:

GF_DIVIDE_DEFAULT

GF_DIVIDE_MATRIX

GF_DIVIDE_EUCLID

prim_poly is the field-defining primitive polynomial

arg1 and arg2 are special arguments usually used for defining SPLIT and GROUP

operations

3.) galois_init_composite_field

Function signature:

gf_t* galois_init_composite_field(int w,

int region_type,

int divide_type,

int degree,

gf_t* base_gf);

This is a helper function designed to make creating Composite fields easier. All you

need to do is hand it w, region mult type, divide type, degree and a pointer to a base

field. Note that the base_gf must have degree w/degree in order for this to work.

For example, if we create a GF using:

galois_init_composite_field(32, GF_REGION_DEFAULT, GF_DIVIDE_DEFAULT, 2, base_gf);

Then base_gf must have w=16.

For more information on how to change the backing fields for Jerasure, please refer to

1.) Examples/reed_sol_test_gf.c: Runs basic tests for Reed-Solomon given args

for a backing GF (uses create_gf_from_argv to get gf_t pointer)

2.) Examples/reed_sol_time_gf.c: Runs more thorough timing and validation tests

for a backing GF (uses create_gf_from_argv to get gf_t pointer)

3.) Examples/reed_sol_hard_time_gf.c: Runs more thorough timing and validation tests

for a backing GF (uses galois_init_field and galois_init_composite_field to get gf_t

pointer)