diff options
Diffstat (limited to 'sysdeps/aarch64/fpu/tanh_sve.c')
| -rw-r--r-- | sysdeps/aarch64/fpu/tanh_sve.c | 100 |
1 files changed, 100 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/tanh_sve.c b/sysdeps/aarch64/fpu/tanh_sve.c new file mode 100644 index 0000000000..d25e011cea --- /dev/null +++ b/sysdeps/aarch64/fpu/tanh_sve.c @@ -0,0 +1,100 @@ +/* Double-precision vector (SVE) 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 "sv_math.h" +#include "poly_sve_f64.h" + +static const struct data +{ + float64_t poly[11]; + float64_t inv_ln2, ln2_hi, ln2_lo, shift; + uint64_t thresh, tiny_bound; +} data = { + /* Generated using Remez, deg=12 in [-log(2)/2, log(2)/2]. */ + .poly = { 0x1p-1, 0x1.5555555555559p-3, 0x1.555555555554bp-5, + 0x1.111111110f663p-7, 0x1.6c16c16c1b5f3p-10, + 0x1.a01a01affa35dp-13, 0x1.a01a018b4ecbbp-16, + 0x1.71ddf82db5bb4p-19, 0x1.27e517fc0d54bp-22, + 0x1.af5eedae67435p-26, 0x1.1f143d060a28ap-29, }, + + .inv_ln2 = 0x1.71547652b82fep0, + .ln2_hi = -0x1.62e42fefa39efp-1, + .ln2_lo = -0x1.abc9e3b39803fp-56, + .shift = 0x1.8p52, + + .tiny_bound = 0x3e40000000000000, /* asuint64 (0x1p-27). */ + /* asuint64(0x1.241bf835f9d5fp+4) - asuint64(tiny_bound). */ + .thresh = 0x01f241bf835f9d5f, +}; + +static inline svfloat64_t +expm1_inline (svfloat64_t x, const svbool_t pg, 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. */ + svfloat64_t j + = svsub_x (pg, svmla_x (pg, sv_f64 (d->shift), x, d->inv_ln2), d->shift); + svint64_t i = svcvt_s64_x (pg, j); + svfloat64_t f = svmla_x (pg, x, j, d->ln2_hi); + f = svmla_x (pg, f, j, d->ln2_lo); + + /* Approximate expm1(f) using polynomial. */ + svfloat64_t f2 = svmul_x (pg, f, f); + svfloat64_t f4 = svmul_x (pg, f2, f2); + svfloat64_t p = svmla_x ( + pg, f, f2, + sv_estrin_10_f64_x (pg, f, f2, f4, svmul_x (pg, f4, f4), d->poly)); + + /* t = 2 ^ i. */ + svfloat64_t t = svscale_x (pg, sv_f64 (1), i); + /* expm1(x) = p * t + (t - 1). */ + return svmla_x (pg, svsub_x (pg, t, 1), p, t); +} + +static svfloat64_t NOINLINE +special_case (svfloat64_t x, svfloat64_t y, svbool_t special) +{ + return sv_call_f64 (tanh, x, y, special); +} + +/* SVE approximation for double-precision tanh(x), using a simplified + version of expm1. The greatest observed error is 2.77 ULP: + _ZGVsMxv_tanh(-0x1.c4a4ca0f9f3b7p-3) got -0x1.bd6a21a163627p-3 + want -0x1.bd6a21a163624p-3. */ +svfloat64_t SV_NAME_D1 (tanh) (svfloat64_t x, svbool_t pg) +{ + const struct data *d = ptr_barrier (&data); + + svuint64_t ia = svreinterpret_u64 (svabs_x (pg, x)); + + /* Trigger special-cases for tiny, boring and infinity/NaN. */ + svbool_t special = svcmpgt (pg, svsub_x (pg, ia, d->tiny_bound), d->thresh); + + svfloat64_t u = svadd_x (pg, x, x); + + /* tanh(x) = (e^2x - 1) / (e^2x + 1). */ + svfloat64_t q = expm1_inline (u, pg, d); + svfloat64_t qp2 = svadd_x (pg, q, 2); + + if (__glibc_unlikely (svptest_any (pg, special))) + return special_case (x, svdiv_x (pg, q, qp2), special); + return svdiv_x (pg, q, qp2); +} |