garfield-lewis wrote:
Hi,
I've got the following datatype:
struct X { __m128i hi; __m128i lo; }
I need to use only SSE 4.2 and below instructions to do a subtraction of 2 of these taking into account possible borrow issues at bits 63-64, 127-128 and 191-192. Does anyone have a quick set of instructions that could be used to accomplish this? Again using SSE 4.2 and earlier instructions.
Thx...
The best solution is to break components of X into scalars:
[cpp] asm ("sub %4, %0;"
"sbb %5, %1;"
"sbb %6, %2;"
"sbb %7, %3;"
: "=r" (*(uint64*) &z.lo),
"=r" (*((uint64*) &z.lo + 1)),
"=r" (*(uint64*) &z.hi),
"=r" (*((uint64*) &z.hi + 1))
: "g" (*(uint64*) &y.lo),
"g" (*((uint64*) &y.lo + 1)),
"g" (*(uint64*) &y.hi),
"g" (*((uint64*) &y.hi + 1)),
"0" (*(uint64*) &x.lo),
"1" (*((uint64*) &x.lo + 1)),
"2" (*(uint64*) &x.hi),
"3" (*((uint64*) &x.hi + 1))
);[/cpp]
