[cfe-dev] ARMv7 float->int rounding

[Joerg Sonnenberger via cfe-dev]

On Thu, Feb 18, 2016 at 02:40:43PM +0100, Domagoj Saric via cfe-dev wrote:
> std::int32_t round( float const floatingPointValue )
> {
> #if A
>   return __builtin_lrintf( floatingPointValue );

lrint is not optimised on any platforms AFAICT, x86 has a small note
about it.

> #elif B
>   std::int32_t integerValue;
>   __asm__
>   (
>     "vcvtr.s32.f32 %0, %1" : "=w"( integerValue ) : "w"( floatingPointValue );
>   );
>   return integerValue;

This doesn't work because the types are wrong. You want to do something
like
      "vcvtr.s32.f32 %1, %1; vmov %0, %1"
or so with =r for the integerValue.  Not sure why this is not caught in
the frontend already.

> #elif C
>   return __builtin_arm_vcvtr_f( floatingPointValue, 0 );

WFM

Joerg