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author | Joe Ramsay <Joe.Ramsay@arm.com> | 2023-10-05 17:10:49 +0100 |
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committer | Szabolcs Nagy <szabolcs.nagy@arm.com> | 2023-10-23 15:00:45 +0100 |
commit | b39e9db5e305365db0c347fd308b7c0d86e3507b (patch) | |
tree | e7fccd5c92b1769601497ce2b83f97405dee54f4 /sysdeps/aarch64/fpu/exp2_advsimd.c | |
parent | f554334c05a95c6b4df532ddc88cd3e72dc7d04c (diff) | |
download | glibc-b39e9db5e305365db0c347fd308b7c0d86e3507b.tar.gz glibc-b39e9db5e305365db0c347fd308b7c0d86e3507b.tar.xz glibc-b39e9db5e305365db0c347fd308b7c0d86e3507b.zip |
aarch64: Add vector implementations of exp2 routines
Some routines reuse table from v_exp_data.c
Diffstat (limited to 'sysdeps/aarch64/fpu/exp2_advsimd.c')
-rw-r--r-- | sysdeps/aarch64/fpu/exp2_advsimd.c | 128 |
1 files changed, 128 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/exp2_advsimd.c b/sysdeps/aarch64/fpu/exp2_advsimd.c new file mode 100644 index 0000000000..8e26033cb9 --- /dev/null +++ b/sysdeps/aarch64/fpu/exp2_advsimd.c @@ -0,0 +1,128 @@ +/* Double-precision vector (AdvSIMD) exp2 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 "v_math.h" +#include "poly_advsimd_f64.h" + +#define N (1 << V_EXP_TABLE_BITS) +#define IndexMask (N - 1) +#define BigBound 1022.0 +#define UOFlowBound 1280.0 + +static const struct data +{ + float64x2_t poly[4]; + float64x2_t shift, scale_big_bound, scale_uoflow_bound; +} data = { + /* Coefficients are computed using Remez algorithm with + minimisation of the absolute error. */ + .poly = { V2 (0x1.62e42fefa3686p-1), V2 (0x1.ebfbdff82c241p-3), + V2 (0x1.c6b09b16de99ap-5), V2 (0x1.3b2abf5571ad8p-7) }, + .shift = V2 (0x1.8p52 / N), + .scale_big_bound = V2 (BigBound), + .scale_uoflow_bound = V2 (UOFlowBound), +}; + +static inline uint64x2_t +lookup_sbits (uint64x2_t i) +{ + return (uint64x2_t){ __v_exp_data[i[0] & IndexMask], + __v_exp_data[i[1] & IndexMask] }; +} + +#if WANT_SIMD_EXCEPT + +# define TinyBound 0x2000000000000000 /* asuint64(0x1p-511). */ +# define Thres 0x2080000000000000 /* asuint64(512.0) - TinyBound. */ + +/* Call scalar exp2 as a fallback. */ +static float64x2_t VPCS_ATTR NOINLINE +special_case (float64x2_t x) +{ + return v_call_f64 (exp2, x, x, v_u64 (0xffffffffffffffff)); +} + +#else + +# define SpecialOffset 0x6000000000000000 /* 0x1p513. */ +/* SpecialBias1 + SpecialBias1 = asuint(1.0). */ +# define SpecialBias1 0x7000000000000000 /* 0x1p769. */ +# define SpecialBias2 0x3010000000000000 /* 0x1p-254. */ + +static float64x2_t VPCS_ATTR +special_case (float64x2_t s, float64x2_t y, float64x2_t n, + const struct data *d) +{ + /* 2^(n/N) may overflow, break it up into s1*s2. */ + uint64x2_t b = vandq_u64 (vclezq_f64 (n), v_u64 (SpecialOffset)); + float64x2_t s1 = vreinterpretq_f64_u64 (vsubq_u64 (v_u64 (SpecialBias1), b)); + float64x2_t s2 = vreinterpretq_f64_u64 ( + vaddq_u64 (vsubq_u64 (vreinterpretq_u64_f64 (s), v_u64 (SpecialBias2)), b)); + uint64x2_t cmp = vcagtq_f64 (n, d->scale_uoflow_bound); + float64x2_t r1 = vmulq_f64 (s1, s1); + float64x2_t r0 = vmulq_f64 (vfmaq_f64 (s2, s2, y), s1); + return vbslq_f64 (cmp, r1, r0); +} + +#endif + +/* Fast vector implementation of exp2. + Maximum measured error is 1.65 ulp. + _ZGVnN2v_exp2(-0x1.4c264ab5b559bp-6) got 0x1.f8db0d4df721fp-1 + want 0x1.f8db0d4df721dp-1. */ +VPCS_ATTR +float64x2_t V_NAME_D1 (exp2) (float64x2_t x) +{ + const struct data *d = ptr_barrier (&data); + uint64x2_t cmp; +#if WANT_SIMD_EXCEPT + uint64x2_t ia = vreinterpretq_u64_f64 (vabsq_f64 (x)); + cmp = vcgeq_u64 (vsubq_u64 (ia, v_u64 (TinyBound)), v_u64 (Thres)); + /* If any special case (inf, nan, small and large x) is detected, + fall back to scalar for all lanes. */ + if (__glibc_unlikely (v_any_u64 (cmp))) + return special_case (x); +#else + cmp = vcagtq_f64 (x, d->scale_big_bound); +#endif + + /* n = round(x/N). */ + float64x2_t z = vaddq_f64 (d->shift, x); + uint64x2_t u = vreinterpretq_u64_f64 (z); + float64x2_t n = vsubq_f64 (z, d->shift); + + /* r = x - n/N. */ + float64x2_t r = vsubq_f64 (x, n); + + /* s = 2^(n/N). */ + uint64x2_t e = vshlq_n_u64 (u, 52 - V_EXP_TABLE_BITS); + u = lookup_sbits (u); + float64x2_t s = vreinterpretq_f64_u64 (vaddq_u64 (u, e)); + + /* y ~ exp2(r) - 1. */ + float64x2_t r2 = vmulq_f64 (r, r); + float64x2_t y = v_pairwise_poly_3_f64 (r, r2, d->poly); + y = vmulq_f64 (r, y); + +#if !WANT_SIMD_EXCEPT + if (__glibc_unlikely (v_any_u64 (cmp))) + return special_case (s, y, n, d); +#endif + return vfmaq_f64 (s, s, y); +} |