wtperf: MSVC complains about float conversion in throttle code

David Hows, in wtperf/wtperf_throttle.c, there's this code:

throttle_cfg->ops_count =

    (uint64_t) (float)(usecs_delta /

    throttle_cfg->usecs_increment) *

    (float)throttle_cfg->ops_per_increment;

throttle_cfg->last_increment = now;

and MSVC complains:

bench\wtperf\wtperf_throttle.c(110): warning C4244: '=': conversion from

'float' to 'uint64_t', possible loss of data

I'm not sure what's going on here – all of the fields are uint64_t, not sure why we're casting everything to float, couldn't we get the same results using an integer expression?

I suspect the warning would go away if we just cast the result of the calculation to uint64_t, but I don't really understand what's going on here.