On 23 March 2014 21:52, Tom Musta <tommu...@gmail.com> wrote:
> The various VSX Convert to Integer instructions should truncate the
> mantissa. This fix forces the softfloat rounding mode to "round to
> zero" prior to performing the conversion. After the conversion is
> completed, the internal rounding mode is restored from the PowerPC
> FPSCR bits.
>
> Signed-off-by: Tom Musta <tommu...@gmail.com>
> ---
> V2: Restored rounding mode prior to checking exceptions per Peter Maydell's
> review.
>
> This bug was discovered when running wget, which does this:
>
> double maxtime;
> struct timeval tmout;
> ...
> tmout.tv_usec = 1000000 * (maxtime - (long) maxtime);
>
> The newest PowerPC 64-bit gcc's are now using xscvdpsxds to perform the cast
> of
> the double to long. A timeout of 0.95 was erroneously rounding up to 1 and
> hence computing a negative timeout value.
>
> It would be great if we could still get this into 2.0.
>
> target-ppc/fpu_helper.c | 4 ++++
> 1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/target-ppc/fpu_helper.c b/target-ppc/fpu_helper.c
> index fd91239..9b3a6f7 100644
> --- a/target-ppc/fpu_helper.c
> +++ b/target-ppc/fpu_helper.c
> @@ -2568,7 +2568,11 @@ void helper_##op(CPUPPCState *env, uint32_t opcode)
> \
> fload_invalid_op_excp(env, POWERPC_EXCP_FP_VXCVI, 0);
> \
> xt.tfld = rnan;
> \
> } else {
> \
> + /* force round to zero mode (truncation) */
> \
> + set_float_rounding_mode(float_round_to_zero, &env->fp_status);
> \
> xt.tfld = stp##_to_##ttp(xb.sfld, &env->fp_status);
> \
> + /* restore rounding mode from FPSCR */
> \
> + fpscr_set_rounding_mode(env);
> \
> if (env->fp_status.float_exception_flags & float_flag_invalid) {
> \
> fload_invalid_op_excp(env, POWERPC_EXCP_FP_VXCVI, 0);
> \
> }
> \
> --
> 1.7.1
Looking at this a little more closely, why aren't we
just using the _round_to_zero versions of the float
to int conversion softfloat functions? (This is how
we implement fctiwz vs fctiw, for instance.)
thanks
-- PMM
