diff options
Diffstat (limited to 'sysdeps/aarch64/fpu/log2_advsimd.c')
| -rw-r--r-- | sysdeps/aarch64/fpu/log2_advsimd.c | 109 |
1 files changed, 109 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/log2_advsimd.c b/sysdeps/aarch64/fpu/log2_advsimd.c new file mode 100644 index 0000000000..4f29924bfa --- /dev/null +++ b/sysdeps/aarch64/fpu/log2_advsimd.c @@ -0,0 +1,109 @@ +/* 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_LOG2_TABLE_BITS) + +static const struct data +{ + uint64x2_t min_norm; + uint32x4_t special_bound; + float64x2_t poly[5]; + float64x2_t invln2; + uint64x2_t sign_exp_mask; +} data = { + /* Each coefficient was generated to approximate log(r) for |r| < 0x1.fp-9 + and N = 128, then scaled by log2(e) in extended precision and rounded back + to double precision. */ + .poly = { V2 (-0x1.71547652b83p-1), V2 (0x1.ec709dc340953p-2), + V2 (-0x1.71547651c8f35p-2), V2 (0x1.2777ebe12dda5p-2), + V2 (-0x1.ec738d616fe26p-3) }, + .invln2 = V2 (0x1.71547652b82fep0), + .min_norm = V2 (0x0010000000000000), /* asuint64(0x1p-1022). */ + .special_bound = V4 (0x7fe00000), /* asuint64(inf) - min_norm. */ + .sign_exp_mask = V2 (0xfff0000000000000), +}; + +#define Off v_u64 (0x3fe6900900000000) +#define IndexMask (N - 1) + +struct entry +{ + float64x2_t invc; + float64x2_t log2c; +}; + +static inline struct entry +lookup (uint64x2_t i) +{ + struct entry e; + uint64_t i0 = (i[0] >> (52 - V_LOG2_TABLE_BITS)) & IndexMask; + uint64_t i1 = (i[1] >> (52 - V_LOG2_TABLE_BITS)) & IndexMask; + float64x2_t e0 = vld1q_f64 (&__v_log2_data.table[i0].invc); + float64x2_t e1 = vld1q_f64 (&__v_log2_data.table[i1].invc); + e.invc = vuzp1q_f64 (e0, e1); + e.log2c = vuzp2q_f64 (e0, e1); + return e; +} + +static float64x2_t VPCS_ATTR NOINLINE +special_case (float64x2_t x, float64x2_t y, float64x2_t w, float64x2_t r2, + uint32x2_t special) +{ + return v_call_f64 (log2, x, vfmaq_f64 (w, r2, y), vmovl_u32 (special)); +} + +/* Double-precision vector log2 routine. Implements the same algorithm as + vector log10, with coefficients and table entries scaled in extended + precision. The maximum observed error is 2.58 ULP: + _ZGVnN2v_log2(0x1.0b556b093869bp+0) got 0x1.fffb34198d9dap-5 + want 0x1.fffb34198d9ddp-5. */ +float64x2_t VPCS_ATTR V_NAME_D1 (log2) (float64x2_t x) +{ + const struct data *d = ptr_barrier (&data); + uint64x2_t ix = vreinterpretq_u64_f64 (x); + uint32x2_t special = vcge_u32 (vsubhn_u64 (ix, d->min_norm), + vget_low_u32 (d->special_bound)); + + /* x = 2^k z; where z is in range [Off,2*Off) and exact. + The range is split into N subintervals. + The ith subinterval contains z and c is near its center. */ + uint64x2_t tmp = vsubq_u64 (ix, Off); + int64x2_t k = vshrq_n_s64 (vreinterpretq_s64_u64 (tmp), 52); + uint64x2_t iz = vsubq_u64 (ix, vandq_u64 (tmp, d->sign_exp_mask)); + float64x2_t z = vreinterpretq_f64_u64 (iz); + + struct entry e = lookup (tmp); + + /* log2(x) = log1p(z/c-1)/log(2) + log2(c) + k. */ + + float64x2_t r = vfmaq_f64 (v_f64 (-1.0), z, e.invc); + float64x2_t kd = vcvtq_f64_s64 (k); + float64x2_t w = vfmaq_f64 (e.log2c, r, d->invln2); + + float64x2_t r2 = vmulq_f64 (r, r); + float64x2_t y = v_pw_horner_4_f64 (r, r2, d->poly); + w = vaddq_f64 (kd, w); + + if (__glibc_unlikely (v_any_u32h (special))) + return special_case (x, y, w, r2, special); + return vfmaq_f64 (w, r2, y); +} |