3 ms·

Do you actually need ctypes here, or can you just use np.reshape? That would cut out the unsafety.

• Retr0id 2y ago
  You can exploit memory unsafety in cpython using only built-in methods, no imports needed at all: https://github.com/DavidBuchanan314/unsafe-python/ https://github.com/DavidBuchanan314/unsafe-python/
  • yosefk 2y ago
    You... probably shouldn't, but, very interesting stuff in that link! I didn't know CPython had no bounds checks in the load_const bytecode op
• im3w1l 2y ago
  I think what you want is a combination of swapaxes and flip (reshape does not turn rows into columns, it turns m input rows into n output rows), but yeah. Actually let me include a little figure original reshape swapaxes abc ab ad def cd be ef cf
• yosefk 2y ago
  I think you'll have a problem with BGR data absent ctypes, since you have a numpy array with the base pointing at the first red channel value, and you want an array with the base pointing 2 bytes before the first red channel value. This is almost definitely "unsafe"?.. or does numpy have functions knowing that due to the negative z stride, the red value before the blue value is within the bounds of the original array? I somehow doubt it though it would be very impressive. And I think the last A value is hopelessly out of reach absent ctypes since a safe API has no information that this last value is within the array bounds; more strictly speaking all the alpha values are out of bounds according to the shape and strides of the BGRA array.