On 03 Jun 2014, at 12:02, Alexander Graf <ag...@suse.de> wrote: > On 06/03/2014 11:14 AM, Tristan Gingold wrote: >> Remove the code that reduce the result to float32 as the frsqrte >> instruction is defined to return a double-precision estimate of >> the reciprocal square root. >> >> Although reducing the fractional part is harmless (as the estimation >> must have at least 12 bits of precision according to the old PEM), >> reducing the exponent range is not correct. >> >> Signed-off-by: Tristan Gingold <ging...@adacore.com> > > I couldn't find a reference to doubles in ISA 2.07. Is frsqrte supposed to > return doubles on all cores?
I have just checked ISA V 2.06 (will download 2.07 if necessary). There are now two instructions: frsqrte and frsqrtes. The second one if for single - so the first one is for double. [ If you look at IBM AIX assembly manual: http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibm.aix.aixassem/doc/alangref/frsqrte.htm they clearly mention that frsqrte operates on double on 603, 604 but not implemented on 601] > Or is this implementation specific? This instruction is optional and the precision of the estimation is implementation dependant. I have looked at some implementation manuals (604, 603, e300) and they don't mention single. > Also, is frsqrte the only instruction affected? Yes. Operation fres operates on single. Tristan. > > > Alex > >> --- >> target-ppc/fpu_helper.c | 3 --- >> 1 file changed, 3 deletions(-) >> >> diff --git a/target-ppc/fpu_helper.c b/target-ppc/fpu_helper.c >> index cd8f015..da93d12 100644 >> --- a/target-ppc/fpu_helper.c >> +++ b/target-ppc/fpu_helper.c >> @@ -977,7 +977,6 @@ uint64_t helper_fres(CPUPPCState *env, uint64_t arg) >> uint64_t helper_frsqrte(CPUPPCState *env, uint64_t arg) >> { >> CPU_DoubleU farg; >> - float32 f32; >> farg.ll = arg; >> @@ -991,8 +990,6 @@ uint64_t helper_frsqrte(CPUPPCState *env, uint64_t arg) >> } >> farg.d = float64_sqrt(farg.d, &env->fp_status); >> farg.d = float64_div(float64_one, farg.d, &env->fp_status); >> - f32 = float64_to_float32(farg.d, &env->fp_status); >> - farg.d = float32_to_float64(f32, &env->fp_status); >> } >> return farg.ll; >> } >
