2024-04-03 11:13:53 +00:00
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/* Double-precision vector (SVE) atanh function
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2025-01-01 18:14:45 +00:00
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Copyright (C) 2024-2025 Free Software Foundation, Inc.
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2024-04-03 11:13:53 +00:00
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#define WANT_SV_LOG1P_K0_SHORTCUT 0
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#include "sv_log1p_inline.h"
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#define One (0x3ff0000000000000)
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#define Half (0x3fe0000000000000)
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static svfloat64_t NOINLINE
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special_case (svfloat64_t x, svfloat64_t y, svbool_t special)
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{
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return sv_call_f64 (atanh, x, y, special);
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}
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/* SVE approximation for double-precision atanh, based on log1p.
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The greatest observed error is 2.81 ULP:
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_ZGVsMxv_atanh(0x1.ffae6288b601p-6) got 0x1.ffd8ff31b5019p-6
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want 0x1.ffd8ff31b501cp-6. */
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svfloat64_t SV_NAME_D1 (atanh) (svfloat64_t x, const svbool_t pg)
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{
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svfloat64_t ax = svabs_x (pg, x);
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svuint64_t iax = svreinterpret_u64 (ax);
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svuint64_t sign = sveor_x (pg, svreinterpret_u64 (x), iax);
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svfloat64_t halfsign = svreinterpret_f64 (svorr_x (pg, sign, Half));
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/* It is special if iax >= 1. */
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// svbool_t special = svcmpge (pg, iax, One);
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svbool_t special = svacge (pg, x, 1.0);
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/* Computation is performed based on the following sequence of equality:
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(1+x)/(1-x) = 1 + 2x/(1-x). */
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svfloat64_t y;
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y = svadd_x (pg, ax, ax);
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y = svdiv_x (pg, y, svsub_x (pg, sv_f64 (1), ax));
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/* ln((1+x)/(1-x)) = ln(1+2x/(1-x)) = ln(1 + y). */
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y = sv_log1p_inline (y, pg);
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if (__glibc_unlikely (svptest_any (pg, special)))
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return special_case (x, svmul_x (pg, halfsign, y), special);
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return svmul_x (pg, halfsign, y);
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}
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