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83 lines
3.1 KiB
C
83 lines
3.1 KiB
C
/* Single-precision vector (AdvSIMD) log10 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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#include "poly_advsimd_f32.h"
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static const struct data
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{
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uint32x4_t min_norm;
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uint16x8_t special_bound;
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float32x4_t poly[8];
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float32x4_t inv_ln10, ln2;
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uint32x4_t off, mantissa_mask;
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} data = {
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/* Use order 9 for log10(1+x), i.e. order 8 for log10(1+x)/x, with x in
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[-1/3, 1/3] (offset=2/3). Max. relative error: 0x1.068ee468p-25. */
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.poly = { V4 (-0x1.bcb79cp-3f), V4 (0x1.2879c8p-3f), V4 (-0x1.bcd472p-4f),
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V4 (0x1.6408f8p-4f), V4 (-0x1.246f8p-4f), V4 (0x1.f0e514p-5f),
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V4 (-0x1.0fc92cp-4f), V4 (0x1.f5f76ap-5f) },
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.ln2 = V4 (0x1.62e43p-1f),
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.inv_ln10 = V4 (0x1.bcb7b2p-2f),
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.min_norm = V4 (0x00800000),
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.special_bound = V8 (0x7f00), /* asuint32(inf) - min_norm. */
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.off = V4 (0x3f2aaaab), /* 0.666667. */
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.mantissa_mask = V4 (0x007fffff),
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};
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static float32x4_t VPCS_ATTR NOINLINE
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special_case (float32x4_t x, float32x4_t y, float32x4_t p, float32x4_t r2,
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uint16x4_t cmp)
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{
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/* Fall back to scalar code. */
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return v_call_f32 (log10f, x, vfmaq_f32 (y, p, r2), vmovl_u16 (cmp));
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}
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/* Fast implementation of AdvSIMD log10f,
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uses a similar approach as AdvSIMD logf with the same offset (i.e., 2/3) and
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an order 9 polynomial.
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Maximum error: 3.305ulps (nearest rounding.)
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_ZGVnN4v_log10f(0x1.555c16p+0) got 0x1.ffe2fap-4
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want 0x1.ffe2f4p-4. */
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float32x4_t VPCS_ATTR V_NAME_F1 (log10) (float32x4_t x)
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{
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const struct data *d = ptr_barrier (&data);
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uint32x4_t u = vreinterpretq_u32_f32 (x);
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uint16x4_t special = vcge_u16 (vsubhn_u32 (u, d->min_norm),
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vget_low_u16 (d->special_bound));
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/* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */
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u = vsubq_u32 (u, d->off);
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float32x4_t n = vcvtq_f32_s32 (
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vshrq_n_s32 (vreinterpretq_s32_u32 (u), 23)); /* signextend. */
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u = vaddq_u32 (vandq_u32 (u, d->mantissa_mask), d->off);
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float32x4_t r = vsubq_f32 (vreinterpretq_f32_u32 (u), v_f32 (1.0f));
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/* y = log10(1+r) + n * log10(2). */
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float32x4_t r2 = vmulq_f32 (r, r);
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float32x4_t poly = v_pw_horner_7_f32 (r, r2, d->poly);
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/* y = Log10(2) * n + poly * InvLn(10). */
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float32x4_t y = vfmaq_f32 (r, d->ln2, n);
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y = vmulq_f32 (y, d->inv_ln10);
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if (__glibc_unlikely (v_any_u16h (special)))
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return special_case (x, y, poly, r2, special);
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return vfmaq_f32 (y, poly, r2);
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}
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