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Thanks for the hint with SET_RESTORE_ROUND macro. Here is the updated version. Tested on s390/s390x. Ok for commit? Bye --- 2014-04-14 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. --- On 04/11/2014 02:50 PM, Adhemerval Zanella wrote:
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.
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