64-bit versions of round and trunc, using SSE intrinsics

It took me two hours to figure this out. Not sure if that's a good thing or a bad thing, but it's a thing.

#include "intrin.h"

inline int round(double x)
{
    return(_mm_cvtsd_si32(_mm_set_sd(x)));
}

inline int trunc(double x)
{
    return(_mm_cvttsd_si32(_mm_set_sd(x)));
}

inline __int64 round64(double x)
{
    return(_mm_cvtsd_si64x(_mm_set_sd(x)));
}

inline __int64 trunc64(double x)
{
    return(_mm_cvttsd_si64x(_mm_set_sd(x)));
}

I benchmarked these carefully on Intel Xeon E5520. The intrinsic SSE round is almost twice as fast as the conditional offset and trunc method:

inline int round(double x)
{
    return(int(x > 0 ? x + 0.5 : x - 0.5));
}

Which is understandable, since the intrinsic SSE round compiles to a single instruction:

cvtsd2si    eax,xmm0 

whereas the conditional offset and trunc method compiles to:

xorpd       xmm7,xmm7 ; xmm7 = 0
movsd       xmm2,0.5 ; xmm2 = 0.5
comisd      xmm1,xmm7  ; x > 0?
jbe         $1  ; n, skip to neg case
movsd       xmm0,xmm1 
addsd       xmm0,xmm2  ; x += 0.5
jmp         $2
$1:
movsd       xmm0,xmm1 
subsd       xmm0,xmm2  ; x -= 0.5
$2:
cvttsd2si   eax,xmm0  ; eax = trunc(x)