diff options
Diffstat (limited to 'sysdeps/aarch64/fpu/tanh_advsimd.c')
| -rw-r--r-- | sysdeps/aarch64/fpu/tanh_advsimd.c | 109 |
1 files changed, 109 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/tanh_advsimd.c b/sysdeps/aarch64/fpu/tanh_advsimd.c new file mode 100644 index 0000000000..1da1dfa5db --- /dev/null +++ b/sysdeps/aarch64/fpu/tanh_advsimd.c @@ -0,0 +1,109 @@ +/* Double-precision vector (Advanced SIMD) tanh function + + Copyright (C) 2024 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 "poly_advsimd_f64.h" + +static const struct data +{ + float64x2_t poly[11]; + float64x2_t inv_ln2, ln2_hi, ln2_lo, shift; + uint64x2_t onef; + uint64x2_t thresh, tiny_bound; +} data = { + /* Generated using Remez, deg=12 in [-log(2)/2, log(2)/2]. */ + .poly = { V2 (0x1p-1), V2 (0x1.5555555555559p-3), V2 (0x1.555555555554bp-5), + V2 (0x1.111111110f663p-7), V2 (0x1.6c16c16c1b5f3p-10), + V2 (0x1.a01a01affa35dp-13), V2 (0x1.a01a018b4ecbbp-16), + V2 (0x1.71ddf82db5bb4p-19), V2 (0x1.27e517fc0d54bp-22), + V2 (0x1.af5eedae67435p-26), V2 (0x1.1f143d060a28ap-29), }, + + .inv_ln2 = V2 (0x1.71547652b82fep0), + .ln2_hi = V2 (-0x1.62e42fefa39efp-1), + .ln2_lo = V2 (-0x1.abc9e3b39803fp-56), + .shift = V2 (0x1.8p52), + + .onef = V2 (0x3ff0000000000000), + .tiny_bound = V2 (0x3e40000000000000), /* asuint64 (0x1p-27). */ + /* asuint64(0x1.241bf835f9d5fp+4) - asuint64(tiny_bound). */ + .thresh = V2 (0x01f241bf835f9d5f), +}; + +static inline float64x2_t +expm1_inline (float64x2_t x, const struct data *d) +{ + /* Helper routine for calculating exp(x) - 1. Vector port of the helper from + the scalar variant of tanh. */ + + /* Reduce argument: f in [-ln2/2, ln2/2], i is exact. */ + float64x2_t j = vsubq_f64 (vfmaq_f64 (d->shift, d->inv_ln2, x), d->shift); + int64x2_t i = vcvtq_s64_f64 (j); + float64x2_t f = vfmaq_f64 (x, j, d->ln2_hi); + f = vfmaq_f64 (f, j, d->ln2_lo); + + /* Approximate expm1(f) using polynomial. */ + float64x2_t f2 = vmulq_f64 (f, f); + float64x2_t f4 = vmulq_f64 (f2, f2); + float64x2_t p = vfmaq_f64 ( + f, f2, v_estrin_10_f64 (f, f2, f4, vmulq_f64 (f4, f4), d->poly)); + + /* t = 2 ^ i. */ + float64x2_t t = vreinterpretq_f64_u64 ( + vaddq_u64 (vreinterpretq_u64_s64 (i << 52), d->onef)); + /* expm1(x) = p * t + (t - 1). */ + return vfmaq_f64 (vsubq_f64 (t, v_f64 (1)), p, t); +} + +static float64x2_t NOINLINE VPCS_ATTR +special_case (float64x2_t x, float64x2_t y, uint64x2_t special) +{ + return v_call_f64 (tanh, x, y, special); +} + +/* Vector approximation for double-precision tanh(x), using a simplified + version of expm1. The greatest observed error is 2.77 ULP: + _ZGVnN2v_tanh(-0x1.c4a4ca0f9f3b7p-3) got -0x1.bd6a21a163627p-3 + want -0x1.bd6a21a163624p-3. */ +float64x2_t VPCS_ATTR V_NAME_D1 (tanh) (float64x2_t x) +{ + const struct data *d = ptr_barrier (&data); + + uint64x2_t ia = vreinterpretq_u64_f64 (vabsq_f64 (x)); + + float64x2_t u = x; + + /* Trigger special-cases for tiny, boring and infinity/NaN. */ + uint64x2_t special = vcgtq_u64 (vsubq_u64 (ia, d->tiny_bound), d->thresh); +#if WANT_SIMD_EXCEPT + /* To trigger fp exceptions correctly, set special lanes to a neutral value. + They will be fixed up later by the special-case handler. */ + if (__glibc_unlikely (v_any_u64 (special))) + u = v_zerofy_f64 (u, special); +#endif + + u = vaddq_f64 (u, u); + + /* tanh(x) = (e^2x - 1) / (e^2x + 1). */ + float64x2_t q = expm1_inline (u, d); + float64x2_t qp2 = vaddq_f64 (q, v_f64 (2)); + + if (__glibc_unlikely (v_any_u64 (special))) + return special_case (x, vdivq_f64 (q, qp2), special); + return vdivq_f64 (q, qp2); +} |