1
$\begingroup$

i have an arbitrary "reshaping" function which, given a linear sequential array can "reshape" it to 2D or 3D. the order in which the X-dimension, Y-dimension and Z-dimension may all be changed, as well as the size of the X, Y and Z dimensions, may all be changed, at runtime. consequently it is not possible to use static compilers or static allocation.

here is a function that, for the full sequential range, prints out a corresponding (remapped) set of indices:

(xdim, ydim, zdim) = (3, 2, 5)
lims = [xdim, ydim, zdim]
idxs = [0,0,0]
order = [1,0,2]

for idx in range(xdim * ydim * zdim):
    new_idx = idxs[0] + idxs[1] * xdim + idxs[2] * xdim * ydim
    print new_idx,
    for i in range(3):
        idxs[order[i]] = idxs[order[i]] + 1
        if (idxs[order[i]] != lims[order[i]]):
            break
        print
    idxs[order[i]] = 0

what i actually need is a function which, when it is passed an arbitrary index, returns one (correct) remapped index.

i suppose what i could hypothetically do is have a function that sets up the full array (at startup time), and indexes it. i would however like to see an algorithmic version of the above.

$\endgroup$
4
  • $\begingroup$ Welcome to Computer Science! It might be a surprise to you, but your question is off-topic here: we deal with computer science questions, not programming questions. Please see our help on topic. Your question might be on-topic on Stack Overflow. $\endgroup$
    – John L.
    Nov 3, 2018 at 11:03
  • $\begingroup$ interesting, thanks jack. i'm probably going to store the full state. the algorithm itself is unusual: dynamic dimensional reshaping is not something i've seen done before. it's actually to be used in the design of a 3D GPU, to allow contiguous registers containing arbitrary-arranged matrices to be multiplied and added. $\endgroup$
    – lkcl
    Nov 3, 2018 at 11:18
  • $\begingroup$ If you can read the code and translate it to pseudocode, it might become on-topic if you have a specific question about how the algorithm works. By the way, you are supposed to provide a url or reference to the origin of the "reshaping" function if you want to post your question anywhere. $\endgroup$
    – John L.
    Nov 3, 2018 at 11:24
  • $\begingroup$ lists.libre-riscv.org/pipermail/libre-riscv-dev/2018-October/… and lists.libre-riscv.org/pipermail/libre-riscv-dev/2018-October/… where there is a reference to an LLVM discussion about Matrices from Vulkan3D - apologies i appreciate this isn't an "academic" reference! $\endgroup$
    – lkcl
    Nov 7, 2018 at 7:03

1 Answer 1

1
$\begingroup$

If the index of $(i,j,k)$ is $p = i + xj + xyk$ then you can compute $i,j,k$ given $p$ as follows:

i = p mod x
j = (p / x) mod y
k = (p / x) / y

Using this you can solve your problem.

$\endgroup$
1
  • $\begingroup$ that makess sense, yuval. then it becomes possible to treat i j k as an array, and also x y z as an array. thanks! $\endgroup$
    – lkcl
    Nov 7, 2018 at 7:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.