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78c01a5cbe
Optimised implementations for single and double precision, Advanced SIMD and SVE, copied from Arm Optimized Routines. Log lookup table added as HIDDEN symbol to allow it to be shared between AdvSIMD and SVE variants. As previously, data tables are used via a barrier to prevent overly aggressive constant inlining. Special-case handlers are marked NOINLINE to avoid incurring the penalty of switching call standards unnecessarily. Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
106 lines
3.3 KiB
C
106 lines
3.3 KiB
C
/* Double-precision vector (Advanced SIMD) log function.
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Copyright (C) 2023 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include "v_math.h"
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static const struct data
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{
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float64x2_t poly[5];
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float64x2_t ln2;
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uint64x2_t min_norm, special_bound, sign_exp_mask;
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} data = {
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/* Worst-case error: 1.17 + 0.5 ulp.
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Rel error: 0x1.6272e588p-56 in [ -0x1.fc1p-9 0x1.009p-8 ]. */
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.poly = { V2 (-0x1.ffffffffffff7p-2), V2 (0x1.55555555170d4p-2),
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V2 (-0x1.0000000399c27p-2), V2 (0x1.999b2e90e94cap-3),
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V2 (-0x1.554e550bd501ep-3) },
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.ln2 = V2 (0x1.62e42fefa39efp-1),
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.min_norm = V2 (0x0010000000000000),
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.special_bound = V2 (0x7fe0000000000000), /* asuint64(inf) - min_norm. */
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.sign_exp_mask = V2 (0xfff0000000000000)
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};
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#define A(i) d->poly[i]
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#define N (1 << V_LOG_TABLE_BITS)
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#define IndexMask (N - 1)
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#define Off v_u64 (0x3fe6900900000000)
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struct entry
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{
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float64x2_t invc;
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float64x2_t logc;
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};
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static inline struct entry
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lookup (uint64x2_t i)
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{
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/* Since N is a power of 2, n % N = n & (N - 1). */
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struct entry e;
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e.invc[0] = __v_log_data.invc[i[0] & IndexMask];
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e.logc[0] = __v_log_data.logc[i[0] & IndexMask];
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e.invc[1] = __v_log_data.invc[i[1] & IndexMask];
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e.logc[1] = __v_log_data.logc[i[1] & IndexMask];
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return e;
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}
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static float64x2_t VPCS_ATTR NOINLINE
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special_case (float64x2_t x, float64x2_t y, uint64x2_t cmp)
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{
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return v_call_f64 (log, x, y, cmp);
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}
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float64x2_t VPCS_ATTR V_NAME_D1 (log) (float64x2_t x)
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{
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const struct data *d = ptr_barrier (&data);
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float64x2_t z, r, r2, p, y, kd, hi;
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uint64x2_t ix, iz, tmp, cmp;
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int64x2_t k;
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struct entry e;
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ix = vreinterpretq_u64_f64 (x);
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cmp = vcgeq_u64 (vsubq_u64 (ix, d->min_norm), d->special_bound);
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/* x = 2^k z; where z is in range [Off,2*Off) and exact.
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The range is split into N subintervals.
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The ith subinterval contains z and c is near its center. */
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tmp = vsubq_u64 (ix, Off);
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k = vshrq_n_s64 (vreinterpretq_s64_u64 (tmp), 52); /* arithmetic shift. */
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iz = vsubq_u64 (ix, vandq_u64 (tmp, d->sign_exp_mask));
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z = vreinterpretq_f64_u64 (iz);
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e = lookup (vshrq_n_u64 (tmp, 52 - V_LOG_TABLE_BITS));
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/* log(x) = log1p(z/c-1) + log(c) + k*Ln2. */
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r = vfmaq_f64 (v_f64 (-1.0), z, e.invc);
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kd = vcvtq_f64_s64 (k);
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/* hi = r + log(c) + k*Ln2. */
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hi = vfmaq_f64 (vaddq_f64 (e.logc, r), kd, d->ln2);
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/* y = r2*(A0 + r*A1 + r2*(A2 + r*A3 + r2*A4)) + hi. */
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r2 = vmulq_f64 (r, r);
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y = vfmaq_f64 (A (2), A (3), r);
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p = vfmaq_f64 (A (0), A (1), r);
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y = vfmaq_f64 (y, A (4), r2);
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y = vfmaq_f64 (p, y, r2);
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y = vfmaq_f64 (hi, y, r2);
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if (__glibc_unlikely (v_any_u64 (cmp)))
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return special_case (x, y, cmp);
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return y;
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}
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