/// <summary>
/// Swap the first m*n elements within a given array so that, for any
/// non-negative i and j less than m and n respectively, dst[i*n+j] == src[j*m+i]
/// </summary>
/// <typeparam name="T">Elements of the array are this type</typeparam>
/// <param name="src">The source elements of the transpose. Must contain at least m*n elements.</param>
/// <param name="dst">Where to write the transpose. Note that dst cannot be the same as src. Must contain at least m*n elements.</param>
/// <param name="m">The major index.</param>
/// <param name="n">The minor index. Elements are currently stored in "m" blocks of "n" items.</param>
public static void Transpose <T>(T[] src, T[] dst, int m, int n)
{
Contracts.AssertValue(src);
Contracts.AssertValue(dst);
Contracts.Assert(src != dst, "Transpose in place not supported");
Contracts.Assert(src.Length <= m * n);
Contracts.Assert(dst.Length <= m * n);
MadeObjectPool <T[]> workPool = new MadeObjectPool <T[]>(() => new T[_block * _block]);
int isteps = (m - 1) / _block + 1;
int jsteps = (n - 1) / _block + 1;
IEnumerable <int> jenum = Enumerable.Range(0, jsteps).Select(j => j * _block);
IEnumerable <int> ienum = Enumerable.Range(0, isteps).Select(i => i * _block);
IEnumerable <Tuple <int, int> > ijenum = ienum.SelectMany(i => jenum.Select(j => new Tuple <int, int>(i, j)));
Parallel.ForEach(ijenum, ij =>
{
int i = ij.Item1;
int j = ij.Item2;
int iend = Math.Min(m - i, _block);
int jend = Math.Min(n - j, _block);
T[] work = workPool.Get();
// Copy things over to the work block.
int off = j * m + i;
for (int jsub = 0; jsub < jend; ++jsub)
{
int workoff = jsub * _block;
for (int isub = 0; isub < iend; ++isub)
{
//work[jsub * BLOCK + isub] = a[(j + jsub) * m + (i + isub)];
work[workoff + isub] = src[off + isub];
}
off += m;
}
// Copy the elements of the work block over to B.
off = i * n + j;
for (int isub = 0; isub < iend; ++isub)
{
for (int jsub = 0; jsub < jend; ++jsub)
{
//dst[(i + isub) * n + (j + jsub)] = work[jsub * BLOCK + isub];
dst[off + jsub] = work[jsub * _block + isub];
}
off += n;
}
workPool.Return(work);
});
}
/// <summary>
/// Swap the first m*n elements within a given array so that, for any
/// non-negative i and j less than m and n respectively, b[i*n+j] == a[j*m+i]
/// </summary>
/// <param name="src"></param>
/// <param name="dst">Where to write the transpose. Note that dst cannot be the same as src.</param>
/// <param name="m"></param>
/// <param name="n"></param>
public static unsafe void Transpose(double *src, double *dst, int m, int n)
{
MadeObjectPool <double[]> workPool = new MadeObjectPool <double[]>(() => new double[_block * _block]);
//T[] work = new T[BLOCK * BLOCK];
int isteps = (m - 1) / _block + 1;
int jsteps = (n - 1) / _block + 1;
IEnumerable <int> jenum = Enumerable.Range(0, jsteps).Select(j => j * _block);
IEnumerable <int> ienum = Enumerable.Range(0, isteps).Select(i => i * _block);
IEnumerable <Tuple <int, int> > ijenum = ienum.SelectMany(i => jenum.Select(j => new Tuple <int, int>(i, j)));
Parallel.ForEach(ijenum, ij =>
{
int i = ij.Item1;
int j = ij.Item2;
int iend = Math.Min(m - i, _block);
int jend = Math.Min(n - j, _block);
double[] work = workPool.Get();
// Copy things over to the work block.
double *srcP = src + j * m + i;
for (int jsub = 0; jsub < jend; ++jsub)
{
for (int isub = 0; isub < iend; ++isub)
{
// This inner loop is equivalent to the following assignment:
// work[j * BLOCK + i] = src[(J + j) * m + (I + i)];
work[jsub * _block + isub] = srcP[isub];
}
srcP += m;
}
// Copy the elements of the work block over to B.
double *dstP = dst + i * n + j;
for (int isub = 0; isub < iend; ++isub)
{
for (int jsub = 0; jsub < jend; ++jsub)
{
// This inner loop is equivalent to the following assignment:
// dst[(I + i) * n + (J + j)] = work[j * BLOCK + i];
dstP[jsub] = work[jsub * _block + isub];
}
dstP += n;
}
workPool.Return(work);
});
}
