mirror of git://sourceware.org/git/glibc.git
72 lines
2.4 KiB
C
72 lines
2.4 KiB
C
/* Double-precision vector (Advanced SIMD) tanh function
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Copyright (C) 2024-2025 Free Software Foundation, Inc.
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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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#include "v_math.h"
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#include "v_expm1_inline.h"
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static const struct data
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{
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struct v_expm1_data d;
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uint64x2_t thresh, tiny_bound;
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} data = {
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.d = V_EXPM1_DATA,
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.tiny_bound = V2 (0x3e40000000000000), /* asuint64 (0x1p-27). */
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/* asuint64(0x1.241bf835f9d5fp+4) - asuint64(tiny_bound). */
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.thresh = V2 (0x01f241bf835f9d5f),
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};
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static float64x2_t NOINLINE VPCS_ATTR
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special_case (float64x2_t x, float64x2_t q, float64x2_t qp2,
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uint64x2_t special)
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{
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return v_call_f64 (tanh, x, vdivq_f64 (q, qp2), special);
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}
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/* Vector approximation for double-precision tanh(x), using a simplified
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version of expm1. The greatest observed error is 2.70 ULP:
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_ZGVnN2v_tanh(-0x1.c59aa220cb177p-3) got -0x1.be5452a6459fep-3
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want -0x1.be5452a6459fbp-3. */
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float64x2_t VPCS_ATTR V_NAME_D1 (tanh) (float64x2_t x)
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{
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const struct data *d = ptr_barrier (&data);
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uint64x2_t ia = vreinterpretq_u64_f64 (vabsq_f64 (x));
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float64x2_t u = x;
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/* Trigger special-cases for tiny, boring and infinity/NaN. */
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uint64x2_t special = vcgtq_u64 (vsubq_u64 (ia, d->tiny_bound), d->thresh);
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#if WANT_SIMD_EXCEPT
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/* To trigger fp exceptions correctly, set special lanes to a neutral value.
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They will be fixed up later by the special-case handler. */
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if (__glibc_unlikely (v_any_u64 (special)))
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u = v_zerofy_f64 (u, special);
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#endif
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u = vaddq_f64 (u, u);
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/* tanh(x) = (e^2x - 1) / (e^2x + 1). */
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float64x2_t q = expm1_inline (u, &d->d);
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float64x2_t qp2 = vaddq_f64 (q, v_f64 (2.0));
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if (__glibc_unlikely (v_any_u64 (special)))
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return special_case (x, q, qp2, special);
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return vdivq_f64 (q, qp2);
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}
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