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
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