I tested it on that too. A problem I usually give a model to test is to optimise already well optimised function that performs certain calculations. I give it reference to CPU instruction set, how instructions can be paired to take advantage of superscalar execution pipeline etc. In that test also it fell on its face by producing code that was demonstrably slower and with extra bug.
Interesting, thanks for sharing. That is something I would have expected it to do well on, unless it tripped the internal rerouting. My experience on computational geometry problems has been universally positive (virtually flawless), and falling back to Opus has been a huge and frustrating step back. Opus has been frequently making errors and regressions, Fable never made a single one.