diff options
Diffstat (limited to 'sysdeps/aarch64/fpu/log2f_advsimd.c')
| -rw-r--r-- | sysdeps/aarch64/fpu/log2f_advsimd.c | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/log2f_advsimd.c b/sysdeps/aarch64/fpu/log2f_advsimd.c new file mode 100644 index 0000000000..e913bcda18 --- /dev/null +++ b/sysdeps/aarch64/fpu/log2f_advsimd.c @@ -0,0 +1,77 @@ +/* Single-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_f32.h" + +static const struct data +{ + uint32x4_t min_norm; + uint16x8_t special_bound; + uint32x4_t off, mantissa_mask; + float32x4_t poly[9]; +} data = { + /* Coefficients generated using Remez algorithm approximate + log2(1+r)/r for r in [ -1/3, 1/3 ]. + rel error: 0x1.c4c4b0cp-26. */ + .poly = { V4 (0x1.715476p0f), /* (float)(1 / ln(2)). */ + V4 (-0x1.715458p-1f), V4 (0x1.ec701cp-2f), V4 (-0x1.7171a4p-2f), + V4 (0x1.27a0b8p-2f), V4 (-0x1.e5143ep-3f), V4 (0x1.9d8ecap-3f), + V4 (-0x1.c675bp-3f), V4 (0x1.9e495p-3f) }, + .min_norm = V4 (0x00800000), + .special_bound = V8 (0x7f00), /* asuint32(inf) - min_norm. */ + .off = V4 (0x3f2aaaab), /* 0.666667. */ + .mantissa_mask = V4 (0x007fffff), +}; + +static float32x4_t VPCS_ATTR NOINLINE +special_case (float32x4_t x, float32x4_t n, float32x4_t p, float32x4_t r, + uint16x4_t cmp) +{ + /* Fall back to scalar code. */ + return v_call_f32 (log2f, x, vfmaq_f32 (n, p, r), vmovl_u16 (cmp)); +} + +/* Fast implementation for single precision AdvSIMD log2, + relies on same argument reduction as AdvSIMD logf. + Maximum error: 2.48 ULPs + _ZGVnN4v_log2f(0x1.558174p+0) got 0x1.a9be84p-2 + want 0x1.a9be8p-2. */ +float32x4_t VPCS_ATTR V_NAME_F1 (log2) (float32x4_t x) +{ + const struct data *d = ptr_barrier (&data); + uint32x4_t u = vreinterpretq_u32_f32 (x); + uint16x4_t special = vcge_u16 (vsubhn_u32 (u, d->min_norm), + vget_low_u16 (d->special_bound)); + + /* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */ + u = vsubq_u32 (u, d->off); + float32x4_t n = vcvtq_f32_s32 ( + vshrq_n_s32 (vreinterpretq_s32_u32 (u), 23)); /* signextend. */ + u = vaddq_u32 (vandq_u32 (u, d->mantissa_mask), d->off); + float32x4_t r = vsubq_f32 (vreinterpretq_f32_u32 (u), v_f32 (1.0f)); + + /* y = log2(1+r) + n. */ + float32x4_t r2 = vmulq_f32 (r, r); + float32x4_t p = v_pw_horner_8_f32 (r, r2, d->poly); + + if (__glibc_unlikely (v_any_u16h (special))) + return special_case (x, n, p, r, special); + return vfmaq_f32 (n, p, r); +} |