this is a small helper for indexing blocks and threads with cuda.

cuINDEX.md

CUDA helper for block and thread indexing

general rule of thumb

threadsperblock = 32
blockspergrid = (an_array.size + (threadsperblock - 1)) // threadsperblock
increment_by_one[blockspergrid, threadsperblock](an_array)

---

Multi dimensional block layout

1 dimensional block layout

blockDim.x is 4, so the marked tile (██) will be executed when, threadIdx.x == 1 and blockIdx.x == 2

B0	T0	T1	T2	T3
B1	T0	T1	T2	T3
B2	T0	██	T2	T3
B3	T0	T1	T2	T3

Launched with:

kernel[4, 4](an_array)

---

2 dimensional block layout

3 x 3 blocks, each with 3 x 3 threads

threadsPerBlock = (3, 3)
b_x = math.ceil(an_array.shape[0] / threadsPerBlock[0])
b_y = math.ceil(an_array.shape[1] / threadsPerBlock[1])
blocksPerGrid = (b_x, b_y)

increment_a_2D_array[blocksPerGrid, threadsPerBlock](an_array)

Block indexes - grid:

[0, 0]	[0, 1]	[0, 2]
[1, 0]	[1, 1]	[1, 2]
[2, 0]	[2, 1]	[2, 2]

threads indexes for each block

[0, 0]	[0, 1]	[0, 2]
[1, 0]	[1, 1]	[1, 2]
[2, 0]	[2, 1]	[2, 2]

representation of the grid, the blocks in it, and the threads in each block

╔═══════════════╦═══════════════╦═══════════════╗
║ Block [0, 0]  ║ Block [0, 1]  ║ Block [0, 2]  ║
║ ┌───┬───┬───┐ ║ ┌───┬───┬───┐ ║ ┌───┬───┬───┐ ║
║ │ 0 │ 1 │ 2 │ ║ │ 0 │ 1 │ 2 │ ║ │ 0 │ 1 │ 2 │ ║
║ ├───┼───┼───┤ ║ ├───┼───┼───┤ ║ ├───┼───┼───┤ ║
║ │ 3 │ 4 │ 5 │ ║ │ 3 │ 4 │ 5 │ ║ │ 3 │ 4 │ 5 │ ║
║ ├───┼───┼───┤ ║ ├───┼───┼───┤ ║ ├───┼───┼───┤ ║
║ │ 6 │ 7 │ 8 │ ║ │ 6 │ 7 │ 8 │ ║ │ 6 │ 7 │ 8 │ ║
║ └───┴───┴───┘ ║ └───┴───┴───┘ ║ └───┴───┴───┘ ║
╠═══════════════╬═══════════════╬═══════════════╣
║ Block [1, 0]  ║ Block [1, 1]  ║ Block [1, 2]  ║
║ ┌───┬───┬───┐ ║ ┌───┬───┬───┐ ║ ┌───┬───┬───┐ ║
║ │ 0 │ 1 │ 2 │ ║ │ 0 │ 1 │ 2 │ ║ │ 0 │ 1 │ 2 │ ║
║ ├───┼───┼───┤ ║ ├───┼───┼───┤ ║ ├───┼───┼───┤ ║
║ │ 3 │ 4 │ 5 │ ║ │ 3 │ 4 │ 5 │ ║ │ 3 │ 4 │ 5 │ ║
║ ├───┼───┼───┤ ║ ├───┼───┼───┤ ║ ├───┼───┼───┤ ║
║ │ 6 │ 7 │ 8 │ ║ │ 6 │ 7 │ 8 │ ║ │ 6 │ 7 │ 8 │ ║
║ └───┴───┴───┘ ║ └───┴───┴───┘ ║ └───┴───┴───┘ ║
╠═══════════════╬═══════════════╬═══════════════╣
║ Block [2, 0]  ║ Block [2, 1]  ║ Block [2, 2]  ║
║ ┌───┬───┬───┐ ║ ┌───┬───┬───┐ ║ ┌───┬───┬───┐ ║
║ │ 0 │ 1 │ 2 │ ║ │ 0 │ 1 │ 2 │ ║ │ 0 │ 1 │ 2 │ ║
║ ├───┼───┼───┤ ║ ├───┼───┼───┤ ║ ├───┼───┼───┤ ║
║ │ 3 │ 4 │ 5 │ ║ │ 3 │ 4 │ 5 │ ║ │ 3 │ 4 │ 5 │ ║
║ ├───┼───┼───┤ ║ ├───┼───┼───┤ ║ ├───┼───┼───┤ ║
║ │ 6 │ 7 │ 8 │ ║ │ 6 │ 7 │ 8 │ ║ │ 6 │ 7 │ 8 │ ║
║ └───┴───┴───┘ ║ └───┴───┴───┘ ║ └───┴───┴───┘ ║
╚═══════════════╩═══════════════╩═══════════════╝