diff options
Diffstat (limited to 'sysdeps/aarch64/fpu/logf_sve.c')
| -rw-r--r-- | sysdeps/aarch64/fpu/logf_sve.c | 87 |
1 files changed, 87 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/logf_sve.c b/sysdeps/aarch64/fpu/logf_sve.c new file mode 100644 index 0000000000..46c6e7c461 --- /dev/null +++ b/sysdeps/aarch64/fpu/logf_sve.c @@ -0,0 +1,87 @@ +/* Single-precision vector (SVE) log function. + + Copyright (C) 2023 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 +{ + float poly_0135[4]; + float poly_246[3]; + float ln2; +} data = { + .poly_0135 = { + /* Coefficients copied from the AdvSIMD routine in math/, then rearranged so + that coeffs 0, 1, 3 and 5 can be loaded as a single quad-word, hence used + with _lane variant of MLA intrinsic. */ + -0x1.3e737cp-3f, 0x1.5a9aa2p-3f, 0x1.961348p-3f, 0x1.555d7cp-2f + }, + .poly_246 = { -0x1.4f9934p-3f, -0x1.00187cp-2f, -0x1.ffffc8p-2f }, + .ln2 = 0x1.62e43p-1f +}; + +#define Min (0x00800000) +#define Max (0x7f800000) +#define Thresh (0x7f000000) /* Max - Min. */ +#define Mask (0x007fffff) +#define Off (0x3f2aaaab) /* 0.666667. */ + +static svfloat32_t NOINLINE +special_case (svfloat32_t x, svfloat32_t y, svbool_t cmp) +{ + return sv_call_f32 (logf, x, y, cmp); +} + +/* Optimised implementation of SVE logf, using the same algorithm and + polynomial as the AdvSIMD routine. Maximum error is 3.34 ULPs: + SV_NAME_F1 (log)(0x1.557298p+0) got 0x1.26edecp-2 + want 0x1.26ede6p-2. */ +svfloat32_t SV_NAME_F1 (log) (svfloat32_t x, const svbool_t pg) +{ + const struct data *d = ptr_barrier (&data); + + svuint32_t u = svreinterpret_u32_f32 (x); + svbool_t cmp = svcmpge_n_u32 (pg, svsub_n_u32_x (pg, u, Min), Thresh); + + /* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */ + u = svsub_n_u32_x (pg, u, Off); + svfloat32_t n + = svcvt_f32_s32_x (pg, svasr_n_s32_x (pg, svreinterpret_s32_u32 (u), + 23)); /* Sign-extend. */ + u = svand_n_u32_x (pg, u, Mask); + u = svadd_n_u32_x (pg, u, Off); + svfloat32_t r = svsub_n_f32_x (pg, svreinterpret_f32_u32 (u), 1.0f); + + /* y = log(1+r) + n*ln2. */ + svfloat32_t r2 = svmul_f32_x (pg, r, r); + /* n*ln2 + r + r2*(P6 + r*P5 + r2*(P4 + r*P3 + r2*(P2 + r*P1 + r2*P0))). */ + svfloat32_t p_0135 = svld1rq_f32 (svptrue_b32 (), &d->poly_0135[0]); + svfloat32_t p = svmla_lane_f32 (sv_f32 (d->poly_246[0]), r, p_0135, 1); + svfloat32_t q = svmla_lane_f32 (sv_f32 (d->poly_246[1]), r, p_0135, 2); + svfloat32_t y = svmla_lane_f32 (sv_f32 (d->poly_246[2]), r, p_0135, 3); + p = svmla_lane_f32 (p, r2, p_0135, 0); + + q = svmla_f32_x (pg, q, r2, p); + y = svmla_f32_x (pg, y, r2, q); + p = svmla_n_f32_x (pg, r, n, d->ln2); + y = svmla_f32_x (pg, p, r2, y); + + if (__glibc_unlikely (svptest_any (pg, cmp))) + return special_case (x, y, cmp); + return y; +} |