I'm writing some optimized functions for gcc-arm in a library that obuses
shorts. So the problem I have is that in extremely many places resutls of my
optimized functions are needlessly sign or zero extended. That is, gcc adds
UXTH or SXTH opcode.
For example, imagine if I use clz instructions (count leading zeros). Result of
the function will be positive number between 0 and 32. So, in places where
result of that clz functions is assigned to a short int it shouldn't
sign-extend the result.
I use inline asm, and it works with arm's armcc if I use short as a result of
inline asm expression:
static __inline short CLZ(int n)
{
short ret;
#ifdef __GNUC__
__asm__("clz %0, %1" : "=r"(ret) : "r"(n));
#else
__asm { clz ret, n; }
#endif
return ret;
}
//test function
short test_clz(int n)
{
return CLZ(n);
}
ARMCC generates this code:
test_clz:
CLZ r0,r0
BX lr
GCC generates this code:
test_clz:
clz r0, r0
sxth r0, r0 <--- offending line.
bx lr
any way to make gcc not sign-extend results?
Thank you
