I am translating a C++ 128-bit arithmetic package for an embedded
environment from Diab asm functions to gcc asm statements wrapped
in C++ inline functions. To minimize loads and stores the original
package used the PPC's string instructions (lswi/stswi). I need to
preserve that size reduction strategy.
Here is my current cut at the assignment operator:
class int128 {
private:
int hi;
unsigned hl;
unsigned lh;
unsigned lo;
public:
int128 const& operator = (int128 const& val);
};
inline int128 const& operator = (int128 const& val)
{
asm ( "lswi 5,%[rhs],16\n"
" stswi 5,%[lhs],16"
: [lhsmem] "=m" (*this)
: [rhsmem] "m" (val)
, [lhs] "b" (this)
, [rhs] "b" (&val)
: "5", "6", "7", "8"
);
return *this;
}
void test(int128& a, int128& b)
{
a = b;
}
This example compiles correctly and generates correct code. Still
I would appreciate feedback on the approach. In particular are the
the fake [rhsmem] and [lhsmem] operands the correct or best way to
express the memory accesses performed by the lswi and stswi?
TIA,
/john
--
John S. Yates, Jr. 508 665-6897 (voice)
Netezza Inc 508 665-6811 (fax)
200 Crossing Blvd. Framingham, MA 01701
