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REFACTOR: Final cleanup of DiscImageChef.Checksums.

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This commit is contained in:
Natalia Portillo
2017-12-23 16:40:14 +00:00
parent d4bfbf2cae
commit bb0b845da8
13 changed files with 251 additions and 232 deletions
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66
DiscImageChef.Checksums/ReedSolomon.cs
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@@ -63,34 +63,40 @@ using DiscImageChef.Console;
namespace DiscImageChef.Checksums
{
/// <summary>
/// Implements the Reed-Solomon algorithm
/// Implements the Reed-Solomon algorithm
/// </summary>
public class ReedSolomon
{
/* Primitive polynomials - see Lin & Costello, Error Control Coding Appendix A,
* and Lee & Messerschmitt, Digital Communication p. 453.
*/
int[] pp;
/* index->polynomial form conversion table */
int[] alpha_to;
/* Polynomial->index form conversion table */
int[] index_of;
/* Generator polynomial g(x)
* Degree of g(x) = 2*TT
* has roots @**B0, @**(B0+1), ... ,@^(B0+2*TT-1)
*/
int[] gg;
int mm, kk, nn;
/* No legal value in index form represents zero, so
* we need a special value for this purpose
*/
int a0;
bool initialized;
/* Alpha exponent for the first root of the generator polynomial */
/// <summary>
/// Alpha exponent for the first root of the generator polynomial
/// </summary>
const int B0 = 1;
/// <summary>
/// No legal value in index form represents zero, so we need a special value for this purpose
/// </summary>
int a0;
/// <summary>
/// index->polynomial form conversion table
/// </summary>
int[] alpha_to;
/// <summary>
/// Generator polynomial g(x) Degree of g(x) = 2*TT has roots @**B0, @**(B0+1), ... ,@^(B0+2*TT-1)
/// </summary>
int[] gg;
/// <summary>
/// Polynomial->index form conversion table
/// </summary>
int[] index_of;
bool initialized;
int mm, kk, nn;
/// <summary>
/// Primitive polynomials - see Lin & Costello, Error Control Coding Appendix A, and Lee & Messerschmitt, Digital
/// Communication p. 453.
/// </summary>
int[] pp;
/// <summary>
/// Initializes the Reed-Solomon with RS(n,k) with GF(2^m)
/// Initializes the Reed-Solomon with RS(n,k) with GF(2^m)
/// </summary>
public void InitRs(int n, int k, int m)
{
@@ -301,7 +307,7 @@ namespace DiscImageChef.Checksums
* data(X)*X**(NN-KK)+ b(X)
*/
/// <summary>
/// Takes the symbols in data to output parity in bb.
/// Takes the symbols in data to output parity in bb.
/// </summary>
/// <returns>Returns -1 if an illegal symbol is found.</returns>
/// <param name="data">Data symbols.</param>
@@ -355,7 +361,7 @@ namespace DiscImageChef.Checksums
* in R. Blahut's "Theory ... of Error-Correcting Codes".
*/
/// <summary>
/// Decodes the RS. If decoding is successful outputs corrected data symbols.
/// Decodes the RS. If decoding is successful outputs corrected data symbols.
/// </summary>
/// <returns>Returns corrected symbols, -1 if illegal or uncorrectable</returns>
/// <param name="data">Data symbols.</param>
@@ -395,8 +401,7 @@ namespace DiscImageChef.Checksums
{
tmp = 0;
for(j = 0; j < nn; j++)
if(recd[j] != a0) /* recd[j] in index form */
tmp ^= alpha_to[Modnn(recd[j] + (B0 + i - 1) * j)];
if(recd[j] != a0) /* recd[j] in index form */ tmp ^= alpha_to[Modnn(recd[j] + (B0 + i - 1) * j)];
synError |= tmp; /* set flag if non-zero syndrome =>
* error */
@@ -473,7 +478,8 @@ namespace DiscImageChef.Checksums
/* r is the step number */
/* Compute discrepancy at the r-th step in poly-form */
int discrR = 0;
for(i = 0; i < r; i++) if(lambda[i] != 0 && s[r - i] != a0) discrR ^= alpha_to[Modnn(index_of[lambda[i]] + s[r - i])];
for(i = 0; i < r; i++)
if(lambda[i] != 0 && s[r - i] != a0) discrR ^= alpha_to[Modnn(index_of[lambda[i]] + s[r - i])];
discrR = index_of[discrR]; /* Index form */
if(discrR == a0)
@@ -560,7 +566,8 @@ namespace DiscImageChef.Checksums
{
tmp = 0;
j = degLambda < i ? degLambda : i;
for(; j >= 0; j--) if(s[i + 1 - j] != a0 && lambda[j] != a0) tmp ^= alpha_to[Modnn(s[i + 1 - j] + lambda[j])];
for(; j >= 0; j--)
if(s[i + 1 - j] != a0 && lambda[j] != a0) tmp ^= alpha_to[Modnn(s[i + 1 - j] + lambda[j])];
if(tmp != 0) degOmega = i;
omega[i] = index_of[tmp];
@@ -581,7 +588,8 @@ namespace DiscImageChef.Checksums
int den = 0;
/* lambda[i+1] for i even is the formal derivative lambda_pr of lambda[i] */
for(i = Min(degLambda, nn - kk - 1) & ~1; i >= 0; i -= 2) if(lambda[i + 1] != a0) den ^= alpha_to[Modnn(lambda[i + 1] + i * root[j])];
for(i = Min(degLambda, nn - kk - 1) & ~1; i >= 0; i -= 2)
if(lambda[i + 1] != a0) den ^= alpha_to[Modnn(lambda[i + 1] + i * root[j])];
if(den == 0)
{