`fp_delay_until` is ignored when the uppermost bit is set

[magnmaeh]

Minimal reproducing example:

#include <flexpret/flexpret.h>
int main(void) {
    fp_delay_until(0xFFFFFFFF);
    return 0;
}

Running the program should keep the emulator going "forever", but it exits almost immediately because the delay until seems to get ignored. This does not happen for fp_delay_until(0x7FFFFFFFF);. (Where the uppoermost bit is not set.)

From waveforms, it seems that the sleep_du signal does not get set from the delay until instruction.

[magnmaeh]

One theory was that this was an optimization issue; the compiler might generate different assembly code for a higher int literal. But that is not the case - I tried doing this for -O0.