void make_ldpc
( int seed, /* Random number seed */
make_method method, /* How to make it */
distrib *d, /* Distribution list specified */
int no4cycle /* Eliminate cycles of length four? */
)
{
mod2entry *e, *f, *g, *h;
int added, uneven, elim4, all_even, n_full, left;
int i, j, k, t, z, cb_N;
int *part, *u;
rand_seed(10*seed+1);
H = mod2sparse_allocate(M,N);
part = column_partition(d,N);
/* Create the initial version of the parity check matrix. */
switch (method)
{
case Evencol:
{
z = 0;
left = part[z];
for (j = 0; j<N; j++)
{ while (left==0)
{ z += 1;
if (z>distrib_size(d))
{ abort();
}
left = part[z];
}
for (k = 0; k<distrib_num(d,z); k++)
{ do
{ i = rand_int(M);
} while (mod2sparse_find(H,i,j));
mod2sparse_insert(H,i,j);
}
left -= 1;
}
break;
}
case Evenboth:
{
cb_N = 0;
for (z = 0; z<distrib_size(d); z++)
{ cb_N += distrib_num(d,z) * part[z];
}
u = chk_alloc (cb_N, sizeof *u);
for (k = cb_N-1; k>=0; k--)
{ u[k] = k%M;
}
uneven = 0;
t = 0;
z = 0;
left = part[z];
for (j = 0; j<N; j++)
{
while (left==0)
{ z += 1;
if (z>distrib_size(d))
{ abort();
}
left = part[z];
}
for (k = 0; k<distrib_num(d,z); k++)
{
for (i = t; i<cb_N && mod2sparse_find(H,u[i],j); i++) ;
if (i==cb_N)
{ uneven += 1;
do
{ i = rand_int(M);
} while (mod2sparse_find(H,i,j));
mod2sparse_insert(H,i,j);
}
else
{ do
{ i = t + rand_int(cb_N-t);
} while (mod2sparse_find(H,u[i],j));
mod2sparse_insert(H,u[i],j);
u[i] = u[t];
t += 1;
}
}
left -= 1;
}
if (uneven>0)
{ fprintf(stderr,"Had to place %d checks in rows unevenly\n",uneven);
}
break;
}
default: abort();
}
/* Add extra bits to avoid rows with less than two checks. */
added = 0;
for (i = 0; i<M; i++)
{ e = mod2sparse_first_in_row(H,i);
if (mod2sparse_at_end(e))
{ j = rand_int(N);
e = mod2sparse_insert(H,i,j);
added += 1;
}
e = mod2sparse_first_in_row(H,i);
if (mod2sparse_at_end(mod2sparse_next_in_row(e)) && N>1)
{ do
{ j = rand_int(N);
} while (j==mod2sparse_col(e));
mod2sparse_insert(H,i,j);
added += 1;
}
}
if (added>0)
{ fprintf(stderr,
"Added %d extra bit-checks to make row counts at least two\n",
added);
}
/* Add extra bits to try to avoid problems with even column counts. */
n_full = 0;
all_even = 1;
for (z = 0; z<distrib_size(d); z++)
{ if (distrib_num(d,z)==M)
{ n_full += part[z];
}
if (distrib_num(d,z)%2==1)
{ all_even = 0;
}
}
if (all_even && N-n_full>1 && added<2)
{ int a;
for (a = 0; added+a<2; a++)
{ do
{ i = rand_int(M);
j = rand_int(N);
} while (mod2sparse_find(H,i,j));
mod2sparse_insert(H,i,j);
}
fprintf(stderr,
"Added %d extra bit-checks to try to avoid problems from even column counts\n",
a);
}
/* Eliminate cycles of length four, if asked, and if possible. */
if (no4cycle)
{
elim4 = 0;
for (t = 0; t<10; t++)
{ k = 0;
for (j = 0; j<N; j++)
{ for (e = mod2sparse_first_in_col(H,j);
!mod2sparse_at_end(e);
e = mod2sparse_next_in_col(e))
{ for (f = mod2sparse_first_in_row(H,mod2sparse_row(e));
!mod2sparse_at_end(f);
f = mod2sparse_next_in_row(f))
{ if (f==e) continue;
for (g = mod2sparse_first_in_col(H,mod2sparse_col(f));
!mod2sparse_at_end(g);
g = mod2sparse_next_in_col(g))
{ if (g==f) continue;
for (h = mod2sparse_first_in_row(H,mod2sparse_row(g));
!mod2sparse_at_end(h);
h = mod2sparse_next_in_row(h))
{ if (mod2sparse_col(h)==j)
{ do
{ i = rand_int(M);
} while (mod2sparse_find(H,i,j));
mod2sparse_delete(H,e);
mod2sparse_insert(H,i,j);
elim4 += 1;
k += 1;
goto nextj;
}
}
}
}
}
nextj: ;
}
if (k==0) break;
}
if (elim4>0)
{ fprintf(stderr,
"Eliminated %d cycles of length four by moving checks within column\n",
elim4);
}
if (t==10)
{ fprintf(stderr,
"Couldn't eliminate all cycles of length four in 10 passes\n");
}
}
}
mod2sparse* CreatePchkMatrix ( int nbRows, int nbCols, make_method makeMethod, int leftDegree, int seed, bool no4cycle, SessionType type, int verbosity )
{
mod2entry *e;
#if 0
mod2entry *f, *g, *h; /* using by no4cycle mode */
int elim4;
#endif
int added, uneven;
int i, j, k, t;
int *u;
mod2sparse *pchkMatrix = NULL;
int skipCols = 0; // avoid warning
int nbDataCols = 0; // avoid warning
if (type != TypeLDGM && type != TypeSTAIRS && type != TypeTRIANGLE) {
fprintf(stderr, "unsupported code type (%d)\n", type);
return NULL;
}
skipCols = nbRows;
nbDataCols = nbCols-skipCols;
// Check for some problems.
if (leftDegree>nbRows)
{
fprintf(stderr, "ERROR, Number of checks per bit (%d) is greater than total checks (%d)\n", leftDegree, nbRows);
return NULL;
}
#if 0
if (leftDegree==nbRows && nbCols>1 && no4cycle)
{
fprintf(stderr, "ERROR, Can't eliminate cycles of length four with this many checks per bit\n");
return NULL;
}
#endif
if (no4cycle) {
fprintf(stderr, "ERROR: no4cycle mode is no longer supported!\n");
exit(-1);
}
ldpc_srand(seed);
pchkMatrix = mod2sparse_allocate(nbRows, nbCols);
/* Create the initial version of the parity check matrix. */
switch (makeMethod)
{
case Evencol:
for(j=skipCols; j<nbCols; j++)
{
for(k=0; k<leftDegree; k++)
{
do
{
i = ldpc_rand(nbRows);
}
while (mod2sparse_find(pchkMatrix,i,j));
mod2sparse_insert(pchkMatrix,i,j);
}
}
break;
case Evenboth:
u = (int*)chk_alloc (leftDegree*nbDataCols, sizeof *u);
/* initialize a list of possible choices to guarantee a homogeneous "1" distribution */
for(k = leftDegree*nbDataCols-1; k>=0; k--)
{
u[k] = k%nbRows;
}
uneven = 0;
t = 0; /* left limit within the list of possible choices, u[] */
for(j = skipCols; j<nbCols; j++) /* for each source symbol column */
{
for(k = 0; k<leftDegree; k++) /* add left_degree "1s" */
{
/* check that valid available choices remain */
for(i = t; i<leftDegree*nbDataCols && mod2sparse_find(pchkMatrix,u[i],j); i++) ;
if(i < leftDegree*nbDataCols)
{
/* choose one index within the list of possible choices */
do {
i = t + ldpc_rand(leftDegree*nbDataCols-t);
} while (mod2sparse_find(pchkMatrix,u[i],j));
mod2sparse_insert(pchkMatrix,u[i],j);
/* replace with u[t] which has never been chosen */
u[i] = u[t];
t++;
}
else
{
/* no choice left, choose one randomly */
uneven += 1;
do {
i = ldpc_rand(nbRows);
} while (mod2sparse_find(pchkMatrix,i,j));
mod2sparse_insert(pchkMatrix,i,j);
}
}
}
if(uneven > 0 && verbosity >= 1)
{
fprintf(stderr,"Had to place %d checks in rows unevenly\n",uneven);
}
free(u); /* VR: added */
break;
default: abort();
}
/* Add extra bits to avoid rows with less than two checks. */
added = 0;
for(i = 0; i<nbRows; i++)
{
e = mod2sparse_first_in_row(pchkMatrix,i);
if(mod2sparse_at_end(e))
{
j = (ldpc_rand(nbDataCols))+skipCols;
e = mod2sparse_insert(pchkMatrix,i,j);
added ++;
}
e = mod2sparse_first_in_row(pchkMatrix,i);
if(mod2sparse_at_end(mod2sparse_next_in_row(e)) && nbDataCols>1)
{
do
{
j = (ldpc_rand(nbDataCols))+skipCols;
} while (j==mod2sparse_col(e));
mod2sparse_insert(pchkMatrix,i,j);
added ++;
}
}
if(added > 0 && verbosity >= 1)
{
fprintf(stderr, "Added %d extra bit-checks to make row counts at least two\n", added);
}
/* Add extra bits to try to avoid problems with even column counts. */
if(leftDegree%2==0 && leftDegree<nbRows && nbDataCols>1 && added<2)
{
int a;
for(a = 0; added+a<2; a++)
{
do
{
i = ldpc_rand(nbRows);
j = (ldpc_rand(nbDataCols))+skipCols;
} while (mod2sparse_find(pchkMatrix,i,j));
mod2sparse_insert(pchkMatrix,i,j);
}
if (verbosity >= 1) {
fprintf(stderr, "Added %d extra bit-checks to try to avoid problems from even column counts\n", a);
}
}
#if 0
/* Eliminate cycles of length four, if asked, and if possible. */
if(no4cycle)
{
elim4 = 0;
for(t = 0; t<10; t++)
{
k = 0;
for(j = 0; j<nbCols; j++)
{
for( e=mod2sparse_first_in_col(pchkMatrix,j); !mod2sparse_at_end(e); e=mod2sparse_next_in_col(e) )
{
for( f=mod2sparse_first_in_row(pchkMatrix,mod2sparse_row(e)); !mod2sparse_at_end(f); f=mod2sparse_next_in_row(f) )
{
if(f==e) continue;
for(g=mod2sparse_first_in_col(pchkMatrix,mod2sparse_col(f)); !mod2sparse_at_end(g); g=mod2sparse_next_in_col(g) )
{
if(g==f) continue;
for( h=mod2sparse_first_in_row(pchkMatrix,mod2sparse_row(g)); !mod2sparse_at_end(h); h = mod2sparse_next_in_row(h) )
{
if(mod2sparse_col(h)==j)
{
do
{
i = ldpc_rand(nbRows);
}
while (mod2sparse_find(pchkMatrix,i,j));
mod2sparse_delete(pchkMatrix,e);
mod2sparse_insert(pchkMatrix,i,j);
elim4 += 1;
k += 1;
goto nextj;
}
}
}
}
}
nextj: ;
}
if(k==0) break;
}
if(elim4>0)
{
fprintf(stderr, "Eliminated %d cycles of length four by moving checks within column\n", elim4);
}
if(t==10)
{
fprintf(stderr, "Couldn't eliminate all cycles of length four in 10 passes\n");
}
}
#endif
switch (type) {
case TypeLDGM:
for (i = 0; i < nbRows; i++) {
/* identity */
mod2sparse_insert(pchkMatrix, i, i);
}
break;
case TypeSTAIRS:
mod2sparse_insert(pchkMatrix, 0, 0); /* 1st row */
for (i = 1; i < nbRows; i++) { /* for all other rows */
/* identity */
mod2sparse_insert(pchkMatrix, i, i);
/* staircase */
mod2sparse_insert(pchkMatrix, i, i-1);
}
break;
case TypeTRIANGLE:
mod2sparse_insert(pchkMatrix, 0, 0); /* 1st row */
for (i = 1; i < nbRows; i++) { /* for all other rows */
/* identity */
mod2sparse_insert(pchkMatrix, i, i);
/* staircase */
mod2sparse_insert(pchkMatrix, i, i-1);
/* triangle */
j = i-1;
for (int l = 0; l < j; l++) { /* limit the # of "1s" added */
j = ldpc_rand(j);
mod2sparse_insert(pchkMatrix, i, j);
}
}
break;
}
return pchkMatrix;
}
