> > generates the same output and same assembly
> > for both casts. can anyone explain what this pragma
> > is supposed to do?
>
> it changes the rounding mode from the standard
> truncate to integer (expensive on a 387) to
> round to nearest (incorrect but cheap).
sure enough. here's timings in µsec for 1<<20 cycles
slow fast factor
amd64 (2.0ghz) 82717 2873 29
xeon 5000 (1.6ghz) 17595 1963 9
core i7 (2.6ghz) 4734 1185 4
> #pragma fpround on
> print("%d\n", (int)d);
> #pragma fpround 0
> print("%d\n", (int)d);
>
> your examples compiles to the same code in both
> cases because the rounding mode is only consulted
> during code generation, which happens at the
> function's final }. you'd need to write two different
> functions to demonstrate the difference.
ah. that escaped me. thanks. it would be good to
document somwhere. would updating /sys/doc/compiler.ms
be a really bad idea?
- erik
