[Mesa3d-dev] [Bug 27286] Mod function returns wrong value

[<bug...@fr...>]

http://bugs.freedesktop.org/show_bug.cgi?id=27286





--- Comment #5 from Brian Paul <bri...@gm...>  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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