| Message ID | li8la8$llb$1@ger.gmane.org |
|---|---|
| State | New |
| Headers | show |
On 11-04-2014 08:56, Stefan Liebler wrote: > Hi, > > on s390 the y1 tests for long double fails due to too large ulps in downward / upward rounding mode (See Bug 16824). > According to Joseph Myers patch comment > (https://sourceware.org/ml/libc-alpha/2014-03/msg00620.html), > round-to-nearest is used internally to reduce error accumulation. > Tests on s390/s390x shows following ulps: > y1: 2 > y1_downward: 4 > y1_towardzero: 2 > y1_upward: 5 > > Is this okay? On other architectures too? > > Bye > --- > 2014-04-11 Stefan Liebler <stli@linux.vnet.ibm.com> > > [BZ #16824] > * sysdeps/ieee754/ldbl-128/e_j1l.c (__ieee754_y1l): > Set round-to-nearest internally to reduce error accumulation. > --- > > diff --git a/sysdeps/ieee754/ldbl-128/e_j1l.c b/sysdeps/ieee754/ldbl-128/e_j1l.c > index 70a1c86..db96c94 100644 > --- a/sysdeps/ieee754/ldbl-128/e_j1l.c > +++ b/sysdeps/ieee754/ldbl-128/e_j1l.c > @@ -855,11 +855,14 @@ __ieee754_y1l (long double x) > return -TWOOPI / x; > if (xx <= 2.0L) > { > + int save_round = fegetround (); > + libc_fesetround (FE_TONEAREST); > /* 0 <= x <= 2 */ > z = xx * xx; > p = xx * neval (z, Y0_2N, NY0_2N) / deval (z, Y0_2D, NY0_2D); > p = -TWOOPI / xx + p; > p = TWOOPI * __ieee754_logl (x) * __ieee754_j1l (x) + p; > + libc_fesetround (save_round); > return p; > } Although s390 does not implemented the optimization to set/restore rounding mode only when needed (check the x86_64 and powerpc fenv_private.h), the way to set/reset rounding mode should using SET_RESTORE_ROUND.
On Fri, Apr 11, 2014 at 01:56:55PM +0200, Stefan Liebler wrote: > Hi, > > on s390 the y1 tests for long double fails due to too large ulps in downward > / upward rounding mode (See Bug 16824). > According to Joseph Myers patch comment > (https://sourceware.org/ml/libc-alpha/2014-03/msg00620.html), > round-to-nearest is used internally to reduce error accumulation. > Tests on s390/s390x shows following ulps: > y1: 2 > y1_downward: 4 > y1_towardzero: 2 > y1_upward: 5 > > Is this okay? On other architectures too? > > Bye > --- > 2014-04-11 Stefan Liebler <stli@linux.vnet.ibm.com> > > [BZ #16824] > * sysdeps/ieee754/ldbl-128/e_j1l.c (__ieee754_y1l): > Set round-to-nearest internally to reduce error accumulation. > --- > > diff --git a/sysdeps/ieee754/ldbl-128/e_j1l.c b/sysdeps/ieee754/ldbl-128/e_j1l.c > index 70a1c86..db96c94 100644 > --- a/sysdeps/ieee754/ldbl-128/e_j1l.c > +++ b/sysdeps/ieee754/ldbl-128/e_j1l.c > @@ -855,11 +855,14 @@ __ieee754_y1l (long double x) > return -TWOOPI / x; > if (xx <= 2.0L) > { > + int save_round = fegetround (); > + libc_fesetround (FE_TONEAREST); You'll find that the SET_RESTORE_ROUND macro would be a better fit here since it does a save/restore only when needed. Besides it makes code more consistent with other functions. Siddhesh. > /* 0 <= x <= 2 */ > z = xx * xx; > p = xx * neval (z, Y0_2N, NY0_2N) / deval (z, Y0_2D, NY0_2D); > p = -TWOOPI / xx + p; > p = TWOOPI * __ieee754_logl (x) * __ieee754_j1l (x) + p; > + libc_fesetround (save_round); > return p; > } > >
diff --git a/sysdeps/ieee754/ldbl-128/e_j1l.c b/sysdeps/ieee754/ldbl-128/e_j1l.c index 70a1c86..db96c94 100644 --- a/sysdeps/ieee754/ldbl-128/e_j1l.c +++ b/sysdeps/ieee754/ldbl-128/e_j1l.c @@ -855,11 +855,14 @@ __ieee754_y1l (long double x) return -TWOOPI / x; if (xx <= 2.0L) { + int save_round = fegetround (); + libc_fesetround (FE_TONEAREST); /* 0 <= x <= 2 */ z = xx * xx; p = xx * neval (z, Y0_2N, NY0_2N) / deval (z, Y0_2D, NY0_2D); p = -TWOOPI / xx + p; p = TWOOPI * __ieee754_logl (x) * __ieee754_j1l (x) + p; + libc_fesetround (save_round); return p; }