http://bugs.freedesktop.org/show_bug.cgi?id=27286
--- Comment #5 from Brian Paul <brian.e.p...@gmail.com> 2010-03-25 17:23:47
PST ---
Off-hand, I _think_ this is an issue with the SSE rcp (reciprocol) instruction.
Per the comment in the code, I think we need to produce a more accurate
result:
static void
emit_rcp (
struct x86_function *func,
unsigned xmm_dst,
unsigned xmm_src )
{
/* On Intel CPUs at least, this is only accurate to 12 bits -- not
* good enough. Need to either emit a proper divide or use the
* iterative technique described below in emit_rsqrt().
*/
sse2_rcpps(
func,
make_xmm( xmm_dst ),
make_xmm( xmm_src ) );
}
Maybe someone handier with SSE can try to fix this. The emit_rsqrt() function
further down uses a Newton-Raphson step to improve the results. That could
help.
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