| 1 | /* Single-precision vector (AdvSIMD) exp2 function |
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| 2 | |
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| 3 | Copyright (C) 2023-2024 Free Software Foundation, Inc. |
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| 4 | This file is part of the GNU C Library. |
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| 5 | |
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| 6 | The GNU C Library is free software; you can redistribute it and/or |
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| 7 | modify it under the terms of the GNU Lesser General Public |
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| 8 | License as published by the Free Software Foundation; either |
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| 9 | version 2.1 of the License, or (at your option) any later version. |
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| 10 | |
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| 11 | The GNU C Library is distributed in the hope that it will be useful, |
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| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 14 | Lesser General Public License for more details. |
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| 15 | |
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| 16 | You should have received a copy of the GNU Lesser General Public |
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| 17 | License along with the GNU C Library; if not, see |
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| 18 | <https://www.gnu.org/licenses/>. */ |
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| 19 | |
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| 20 | #include "v_math.h" |
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| 21 | #include "poly_advsimd_f32.h" |
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| 22 | |
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| 23 | static const struct data |
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| 24 | { |
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| 25 | uint32x4_t min_norm; |
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| 26 | uint16x8_t special_bound; |
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| 27 | uint32x4_t off, mantissa_mask; |
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| 28 | float32x4_t poly[9]; |
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| 29 | } data = { |
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| 30 | /* Coefficients generated using Remez algorithm approximate |
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| 31 | log2(1+r)/r for r in [ -1/3, 1/3 ]. |
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| 32 | rel error: 0x1.c4c4b0cp-26. */ |
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| 33 | .poly = { V4 (0x1.715476p0f), /* (float)(1 / ln(2)). */ |
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| 34 | V4 (-0x1.715458p-1f), V4 (0x1.ec701cp-2f), V4 (-0x1.7171a4p-2f), |
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| 35 | V4 (0x1.27a0b8p-2f), V4 (-0x1.e5143ep-3f), V4 (0x1.9d8ecap-3f), |
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| 36 | V4 (-0x1.c675bp-3f), V4 (0x1.9e495p-3f) }, |
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| 37 | .min_norm = V4 (0x00800000), |
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| 38 | .special_bound = V8 (0x7f00), /* asuint32(inf) - min_norm. */ |
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| 39 | .off = V4 (0x3f2aaaab), /* 0.666667. */ |
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| 40 | .mantissa_mask = V4 (0x007fffff), |
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| 41 | }; |
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| 42 | |
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| 43 | static float32x4_t VPCS_ATTR NOINLINE |
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| 44 | special_case (float32x4_t x, float32x4_t n, float32x4_t p, float32x4_t r, |
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| 45 | uint16x4_t cmp) |
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| 46 | { |
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| 47 | /* Fall back to scalar code. */ |
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| 48 | return v_call_f32 (log2f, x, vfmaq_f32 (n, p, r), vmovl_u16 (cmp)); |
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| 49 | } |
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| 50 | |
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| 51 | /* Fast implementation for single precision AdvSIMD log2, |
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| 52 | relies on same argument reduction as AdvSIMD logf. |
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| 53 | Maximum error: 2.48 ULPs |
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| 54 | _ZGVnN4v_log2f(0x1.558174p+0) got 0x1.a9be84p-2 |
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| 55 | want 0x1.a9be8p-2. */ |
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| 56 | float32x4_t VPCS_ATTR NOINLINE V_NAME_F1 (log2) (float32x4_t x) |
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| 57 | { |
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| 58 | const struct data *d = ptr_barrier (&data); |
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| 59 | uint32x4_t u = vreinterpretq_u32_f32 (x); |
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| 60 | uint16x4_t special = vcge_u16 (vsubhn_u32 (u, d->min_norm), |
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| 61 | vget_low_u16 (d->special_bound)); |
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| 62 | |
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| 63 | /* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */ |
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| 64 | u = vsubq_u32 (u, d->off); |
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| 65 | float32x4_t n = vcvtq_f32_s32 ( |
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| 66 | vshrq_n_s32 (vreinterpretq_s32_u32 (u), 23)); /* signextend. */ |
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| 67 | u = vaddq_u32 (vandq_u32 (u, d->mantissa_mask), d->off); |
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| 68 | float32x4_t r = vsubq_f32 (vreinterpretq_f32_u32 (u), v_f32 (1.0f)); |
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| 69 | |
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| 70 | /* y = log2(1+r) + n. */ |
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| 71 | float32x4_t r2 = vmulq_f32 (r, r); |
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| 72 | float32x4_t p = v_pw_horner_8_f32 (r, r2, d->poly); |
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| 73 | |
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| 74 | if (__glibc_unlikely (v_any_u16h (special))) |
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| 75 | return special_case (x, n, p, r, special); |
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| 76 | return vfmaq_f32 (n, p, r); |
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| 77 | } |
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| 78 | libmvec_hidden_def (V_NAME_F1 (log2)) |
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| 79 | HALF_WIDTH_ALIAS_F1 (log2) |
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| 80 | |
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