unsigned int to float conversion

[FÖLDY Lajos]

Hi guys,

I have some weird results from my program. The suspect is unsigned int to 
float conversion. I have created the following simple test:

// a.cc

void
cvt_u4_f4(unsigned int* u4, float* f4)
{
  *f4=*u4;
}

Compiling it with g++-4.4 -m64 -O3 -S a.cc creates the following listing:

        .file   "a.cc"
        .text
        .p2align 4,,15
.globl _Z9cvt_u4_f4PjPf
        .type   _Z9cvt_u4_f4PjPf, @function
_Z9cvt_u4_f4PjPf:
.LFB0:
        .cfi_startproc
        .cfi_personality 0x3,__gxx_personality_v0
        mov     (%rdi), %eax
        cvtsi2ssq       %rax, %xmm0
        movss   %xmm0, (%rsi)
        ret
        .cfi_endproc
.LFE0:
        .size   _Z9cvt_u4_f4PjPf, .-_Z9cvt_u4_f4PjPf
        .ident  "GCC: (GNU) 4.4.0"
        .section        .note.GNU-stack,"",@progbits


Now, here %eax is filled with the unsigned int value, then %rax is 
converted to float. It seems to me that the higher 32 bit of %rax is never 
set, I miss an xor %rax, %rax before mov. Am I right, or I miss something 
else?

thanks,
lajos