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Diffstat (limited to 'sysdeps/aarch64/fpu/asinpi_sve.c')
| -rw-r--r-- | sysdeps/aarch64/fpu/asinpi_sve.c | 107 |
1 files changed, 107 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/asinpi_sve.c b/sysdeps/aarch64/fpu/asinpi_sve.c new file mode 100644 index 0000000..71ef8ce --- /dev/null +++ b/sysdeps/aarch64/fpu/asinpi_sve.c @@ -0,0 +1,107 @@ +/* Double-Precision vector (SVE) inverse sinpi function + + Copyright (C) 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" + +static const struct data +{ + float64_t c1, c3, c5, c7, c9, c11; + float64_t c0, c2, c4, c6, c8, c10; + float64_t pi_over_2, inv_pi; +} data = { + /* Polynomial approximation of (asin(sqrt(x)) - sqrt(x)) / (x * sqrt(x)) + on [ 0x1p-106, 0x1p-2 ], relative error: 0x1.c3d8e169p-57. */ + .c0 = 0x1.555555555554ep-3, .c1 = 0x1.3333333337233p-4, + .c2 = 0x1.6db6db67f6d9fp-5, .c3 = 0x1.f1c71fbd29fbbp-6, + .c4 = 0x1.6e8b264d467d6p-6, .c5 = 0x1.1c5997c357e9dp-6, + .c6 = 0x1.c86a22cd9389dp-7, .c7 = 0x1.856073c22ebbep-7, + .c8 = 0x1.fd1151acb6bedp-8, .c9 = 0x1.087182f799c1dp-6, + .c10 = -0x1.6602748120927p-7, .c11 = 0x1.cfa0dd1f9478p-6, + .pi_over_2 = 0x1.921fb54442d18p+0, .inv_pi = 0x1.45f306dc9c883p-2, +}; + +/* Double-precision SVE implementation of vector asinpi(x). + + For |x| in [0, 0.5], use an order 11 polynomial P such that the final + approximation is an odd polynomial: asin(x) ~ x + x^3 P(x^2). + + The largest observed error in this region is 1.32 ulp: + _ZGVsMxv_asinpi (0x1.fc12356dbdefbp-2) got 0x1.5272e9658ba66p-3 + want 0x1.5272e9658ba64p-3 + + For |x| in [0.5, 1.0], use same approximation with a change of variable: + asin(x) = pi/2 - (y + y * z * P(z)), with z = (1-x)/2 and y = sqrt(z). + + The largest observed error in this region is 3.48 ulp: + _ZGVsMxv_asinpi (0x1.03da0c2295424p-1) got 0x1.5b02b3dcafaefp-3 + want 0x1.5b02b3dcafaf2p-3. */ +svfloat64_t SV_NAME_D1 (asinpi) (svfloat64_t x, const svbool_t pg) +{ + const struct data *d = ptr_barrier (&data); + svbool_t ptrue = svptrue_b64 (); + + svuint64_t sign = svand_x (pg, svreinterpret_u64 (x), 0x8000000000000000); + svfloat64_t ax = svabs_x (pg, x); + svbool_t a_ge_half = svacge (pg, x, 0.5); + + /* Evaluate polynomial Q(x) = y + y * z * P(z) with + z = x ^ 2 and y = |x| , if |x| < 0.5 + z = (1 - |x|) / 2 and y = sqrt(z), if |x| >= 0.5. */ + svfloat64_t z2 = svsel (a_ge_half, svmls_x (pg, sv_f64 (0.5), ax, 0.5), + svmul_x (ptrue, x, x)); + svfloat64_t z = svsqrt_m (ax, a_ge_half, z2); + + /* Use a single polynomial approximation P for both intervals. */ + svfloat64_t z3 = svmul_x (pg, z2, z); + svfloat64_t z4 = svmul_x (pg, z2, z2); + svfloat64_t z8 = svmul_x (pg, z4, z4); + + svfloat64_t c13 = svld1rq (ptrue, &d->c1); + svfloat64_t c57 = svld1rq (ptrue, &d->c5); + svfloat64_t c911 = svld1rq (ptrue, &d->c9); + + /* Order-11 Estrin scheme. */ + svfloat64_t p01 = svmla_lane (sv_f64 (d->c0), z2, c13, 0); + svfloat64_t p23 = svmla_lane (sv_f64 (d->c2), z2, c13, 1); + svfloat64_t p03 = svmla_x (pg, p01, z4, p23); + + svfloat64_t p45 = svmla_lane (sv_f64 (d->c4), z2, c57, 0); + svfloat64_t p67 = svmla_lane (sv_f64 (d->c6), z2, c57, 1); + svfloat64_t p47 = svmla_x (pg, p45, z4, p67); + + svfloat64_t p89 = svmla_lane (sv_f64 (d->c8), z2, c911, 0); + svfloat64_t p1011 = svmla_lane (sv_f64 (d->c10), z2, c911, 1); + svfloat64_t p811 = svmla_x (pg, p89, z4, p1011); + + svfloat64_t p411 = svmla_x (pg, p47, z8, p811); + svfloat64_t p = svmla_x (pg, p03, z8, p411); + + /* Finalize polynomial: z + z3 * P(z2). */ + p = svmla_x (pg, z, z3, p); + + /* asin(|x|) = Q(|x|) , for |x| < 0.5 + = pi/2 - 2 Q(|x|), for |x| >= 0.5. */ + svfloat64_t y = svmad_m (a_ge_half, p, sv_f64 (-2.0), d->pi_over_2); + + /* Reinsert the sign from the argument. */ + svfloat64_t inv_pi = svreinterpret_f64 ( + svorr_x (pg, svreinterpret_u64 (sv_f64 (d->inv_pi)), sign)); + + return svmul_x (pg, y, inv_pi); +} |