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/* Single-precision vector (SVE) atanh function
Copyright (C) 2024-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include "sv_math.h"
#include "sv_log1pf_inline.h"
#define One (0x3f800000)
#define Half (0x3f000000)
static svfloat32_t NOINLINE
special_case (svuint32_t iax, svuint32_t sign, svfloat32_t halfsign,
svfloat32_t y, svbool_t special)
{
svfloat32_t x = svreinterpret_f32 (sveor_x (svptrue_b32 (), iax, sign));
y = svmul_x (svptrue_b32 (), halfsign, y);
return sv_call_f32 (atanhf, x, y, special);
}
/* Approximation for vector single-precision atanh(x) using modified log1p.
The maximum error is 1.99 ULP:
_ZGVsMxv_atanhf(0x1.f1583p-5) got 0x1.f1f4fap-5
want 0x1.f1f4f6p-5. */
svfloat32_t SV_NAME_F1 (atanh) (svfloat32_t x, const svbool_t pg)
{
svfloat32_t ax = svabs_x (pg, x);
svuint32_t iax = svreinterpret_u32 (ax);
svuint32_t sign = sveor_x (pg, svreinterpret_u32 (x), iax);
svfloat32_t halfsign = svreinterpret_f32 (svorr_x (pg, sign, Half));
svbool_t special = svcmpge (pg, iax, One);
/* Computation is performed based on the following sequence of equality:
* (1+x)/(1-x) = 1 + 2x/(1-x). */
svfloat32_t y = svadd_x (pg, ax, ax);
y = svdiv_x (pg, y, svsub_x (pg, sv_f32 (1), ax));
/* ln((1+x)/(1-x)) = ln(1+2x/(1-x)) = ln(1 + y). */
y = sv_log1pf_inline (y, pg);
if (__glibc_unlikely (svptest_any (pg, special)))
return special_case (iax, sign, halfsign, y, special);
return svmul_x (pg, halfsign, y);
}
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