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/* Double-precision AdvSIMD expm1
Copyright (C) 2023-2025 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 "v_math.h"
#include "v_expm1_inline.h"
static const struct data
{
struct v_expm1_data d;
#if WANT_SIMD_EXCEPT
uint64x2_t thresh, tiny_bound;
#else
float64x2_t oflow_bound;
#endif
} data = {
.d = V_EXPM1_DATA,
#if WANT_SIMD_EXCEPT
/* asuint64(oflow_bound) - asuint64(0x1p-51), shifted left by 1 for abs
compare. */
.thresh = V2 (0x78c56fa6d34b552),
/* asuint64(0x1p-51) << 1. */
.tiny_bound = V2 (0x3cc0000000000000 << 1),
#else
/* Value above which expm1(x) should overflow. Absolute value of the
underflow bound is greater than this, so it catches both cases - there is
a small window where fallbacks are triggered unnecessarily. */
.oflow_bound = V2 (0x1.62b7d369a5aa9p+9),
#endif
};
static float64x2_t VPCS_ATTR NOINLINE
special_case (float64x2_t x, uint64x2_t special, const struct data *d)
{
return v_call_f64 (expm1, x, expm1_inline (v_zerofy_f64 (x, special), &d->d),
special);
}
/* Double-precision vector exp(x) - 1 function.
The maximum error observed error is 2.05 ULP:
_ZGVnN2v_expm1(0x1.634902eaff3adp-2) got 0x1.a8b636e2a9388p-2
want 0x1.a8b636e2a9386p-2. */
float64x2_t VPCS_ATTR V_NAME_D1 (expm1) (float64x2_t x)
{
const struct data *d = ptr_barrier (&data);
#if WANT_SIMD_EXCEPT
uint64x2_t ix = vreinterpretq_u64_f64 (x);
/* If fp exceptions are to be triggered correctly, fall back to scalar for
|x| < 2^-51, |x| > oflow_bound, Inf & NaN. Add ix to itself for
shift-left by 1, and compare with thresh which was left-shifted offline -
this is effectively an absolute compare. */
uint64x2_t special
= vcgeq_u64 (vsubq_u64 (vaddq_u64 (ix, ix), d->tiny_bound), d->thresh);
#else
/* Large input, NaNs and Infs. */
uint64x2_t special = vcageq_f64 (x, d->oflow_bound);
#endif
if (__glibc_unlikely (v_any_u64 (special)))
return special_case (x, special, d);
/* expm1(x) ~= p * t + (t - 1). */
return expm1_inline (x, &d->d);
}
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