Converting 3-plane matrix to 1-plane, strange jit.expr behavior

Hi there,

I want to convert a 1-dimension 3-plane matrix with RGB values to a 1-dimension 1-plane matrix, which I will eventually unroll as a list and send over a serial connection. So principle is:

3-plane matrix : r1 b1 g1, r2 b2 g2, ...
to
1-plane matrix: r1, b1, g1, r2, b2, g2,...

I came up with a jit.expr that works. A bit. 'Cause from cell 65 on it glitches. Then the R value of a cell ends up in the next cell, not the right one. It seems like some kind of rounding error.

Any thoughts on getting this right? Not necessarily using jit.expr.