mirror of
git://sourceware.org/git/glibc.git
synced 2025-03-07 13:28:05 +08:00
8eb5ad2ebc
Remove spurious ADRP and a few MOVs. Reduce memory access by using more indexed MLAs in polynomial. Align notation so that algorithms are easier to compare. Speedup on Neoverse V1 for log10 (8%), log (8.5%), and log2 (10%). Update error threshold in AdvSIMD log (now matches SVE log).
122 lines
4.4 KiB
C
122 lines
4.4 KiB
C
/* Double-precision vector (Advanced SIMD) log function.
|
|
|
|
Copyright (C) 2023-2024 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"
|
|
|
|
static const struct data
|
|
{
|
|
uint64x2_t off, sign_exp_mask, offset_lower_bound;
|
|
uint32x4_t special_bound;
|
|
float64x2_t c0, c2;
|
|
double c1, c3, ln2, c4;
|
|
} data = {
|
|
/* Rel error: 0x1.6272e588p-56 in [ -0x1.fc1p-9 0x1.009p-8 ]. */
|
|
.c0 = V2 (-0x1.ffffffffffff7p-2),
|
|
.c1 = 0x1.55555555170d4p-2,
|
|
.c2 = V2 (-0x1.0000000399c27p-2),
|
|
.c3 = 0x1.999b2e90e94cap-3,
|
|
.c4 = -0x1.554e550bd501ep-3,
|
|
.ln2 = 0x1.62e42fefa39efp-1,
|
|
.sign_exp_mask = V2 (0xfff0000000000000),
|
|
.off = V2 (0x3fe6900900000000),
|
|
/* Lower bound is 0x0010000000000000. For
|
|
optimised register use subnormals are detected after offset has been
|
|
subtracted, so lower bound - offset (which wraps around). */
|
|
.offset_lower_bound = V2 (0x0010000000000000 - 0x3fe6900900000000),
|
|
.special_bound = V4 (0x7fe00000), /* asuint64(inf) - asuint64(0x1p-126). */
|
|
};
|
|
|
|
#define N (1 << V_LOG_TABLE_BITS)
|
|
#define IndexMask (N - 1)
|
|
|
|
struct entry
|
|
{
|
|
float64x2_t invc;
|
|
float64x2_t logc;
|
|
};
|
|
|
|
static inline struct entry
|
|
lookup (uint64x2_t i)
|
|
{
|
|
/* Since N is a power of 2, n % N = n & (N - 1). */
|
|
struct entry e;
|
|
uint64_t i0 = (vgetq_lane_u64 (i, 0) >> (52 - V_LOG_TABLE_BITS)) & IndexMask;
|
|
uint64_t i1 = (vgetq_lane_u64 (i, 1) >> (52 - V_LOG_TABLE_BITS)) & IndexMask;
|
|
float64x2_t e0 = vld1q_f64 (&__v_log_data.table[i0].invc);
|
|
float64x2_t e1 = vld1q_f64 (&__v_log_data.table[i1].invc);
|
|
e.invc = vuzp1q_f64 (e0, e1);
|
|
e.logc = vuzp2q_f64 (e0, e1);
|
|
return e;
|
|
}
|
|
|
|
static float64x2_t VPCS_ATTR NOINLINE
|
|
special_case (float64x2_t hi, uint64x2_t u_off, float64x2_t y, float64x2_t r2,
|
|
uint32x2_t special, const struct data *d)
|
|
{
|
|
float64x2_t x = vreinterpretq_f64_u64 (vaddq_u64 (u_off, d->off));
|
|
return v_call_f64 (log, x, vfmaq_f64 (hi, y, r2), vmovl_u32 (special));
|
|
}
|
|
|
|
/* Double-precision vector log routine.
|
|
The maximum observed error is 2.17 ULP:
|
|
_ZGVnN2v_log(0x1.a6129884398a3p+0) got 0x1.ffffff1cca043p-2
|
|
want 0x1.ffffff1cca045p-2. */
|
|
float64x2_t VPCS_ATTR V_NAME_D1 (log) (float64x2_t x)
|
|
{
|
|
const struct data *d = ptr_barrier (&data);
|
|
|
|
/* To avoid having to mov x out of the way, keep u after offset has been
|
|
applied, and recover x by adding the offset back in the special-case
|
|
handler. */
|
|
uint64x2_t u = vreinterpretq_u64_f64 (x);
|
|
uint64x2_t u_off = vsubq_u64 (u, d->off);
|
|
|
|
/* 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. */
|
|
int64x2_t k = vshrq_n_s64 (vreinterpretq_s64_u64 (u_off), 52);
|
|
uint64x2_t iz = vsubq_u64 (u, vandq_u64 (u_off, d->sign_exp_mask));
|
|
float64x2_t z = vreinterpretq_f64_u64 (iz);
|
|
|
|
struct entry e = lookup (u_off);
|
|
|
|
uint32x2_t special = vcge_u32 (vsubhn_u64 (u_off, d->offset_lower_bound),
|
|
vget_low_u32 (d->special_bound));
|
|
|
|
/* log(x) = log1p(z/c-1) + log(c) + k*Ln2. */
|
|
float64x2_t r = vfmaq_f64 (v_f64 (-1.0), z, e.invc);
|
|
float64x2_t kd = vcvtq_f64_s64 (k);
|
|
|
|
/* hi = r + log(c) + k*Ln2. */
|
|
float64x2_t ln2_and_c4 = vld1q_f64 (&d->ln2);
|
|
float64x2_t hi = vfmaq_laneq_f64 (vaddq_f64 (e.logc, r), kd, ln2_and_c4, 0);
|
|
|
|
/* y = r2*(A0 + r*A1 + r2*(A2 + r*A3 + r2*A4)) + hi. */
|
|
float64x2_t odd_coeffs = vld1q_f64 (&d->c1);
|
|
float64x2_t r2 = vmulq_f64 (r, r);
|
|
float64x2_t y = vfmaq_laneq_f64 (d->c2, r, odd_coeffs, 1);
|
|
float64x2_t p = vfmaq_laneq_f64 (d->c0, r, odd_coeffs, 0);
|
|
y = vfmaq_laneq_f64 (y, r2, ln2_and_c4, 1);
|
|
y = vfmaq_f64 (p, r2, y);
|
|
|
|
if (__glibc_unlikely (v_any_u32h (special)))
|
|
return special_case (hi, u_off, y, r2, special, d);
|
|
return vfmaq_f64 (hi, y, r2);
|
|
}
|