fp.

  > d = trunc(x/y);     // floor works for unsigned
  >
  > // NOTE: if only want 'd' and it's being converted to an
  > // integer then the truncate or floor operation is
  > // free in the float to integer conversion.

Please show me how to portably truncate or floor a floating point value to an int in C for "free".

mtklein•14m ago

They're typically like a 3-cycle op, right? Obviously that's not zero, but as far as floating point ops get it's a cheap as it gets, like an add, mul, fma, that sorta thing.

ranger_danger•9m ago

Perhaps they meant implicit instead of free, since the comment also explains that `d` is an integer and the intent is to truncate, so the trunc() call is not even necessary when the assigning type is an int.

juancn•8m ago

I would love to have some benchmarks for this on some reasonably practical scenario.

In many common cases shift and masking can replace integer division (i.e. hash tables) and you avoid division altogether, and that probably has about the cost of converting an int to a float.

taeric•4m ago

I'm curious that the latency of these is actually worse than the latency of floating operations. Yes, they are worse than many integer instructions, but they seem to be on basically the same order as the equivalent float operations?