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author | Joe Ramsay <Joe.Ramsay@arm.com> | 2023-11-03 12:12:23 +0000 |
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committer | Szabolcs Nagy <szabolcs.nagy@arm.com> | 2023-11-10 17:07:43 +0000 |
commit | 3548a4f0872aefa1f0b636a2d89fde96e5b7d46f (patch) | |
tree | bddfae80edaa1bbbb4daeed167bda5952da616f6 /sysdeps/aarch64/fpu/log1p_advsimd.c | |
parent | b07038c5d304a7afc312516ce0ff886a57bf3163 (diff) | |
download | glibc-3548a4f0872aefa1f0b636a2d89fde96e5b7d46f.tar.gz glibc-3548a4f0872aefa1f0b636a2d89fde96e5b7d46f.tar.xz glibc-3548a4f0872aefa1f0b636a2d89fde96e5b7d46f.zip |
aarch64: Add vector implementations of log1p routines
May discard sign of zero.
Diffstat (limited to 'sysdeps/aarch64/fpu/log1p_advsimd.c')
-rw-r--r-- | sysdeps/aarch64/fpu/log1p_advsimd.c | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/log1p_advsimd.c b/sysdeps/aarch64/fpu/log1p_advsimd.c new file mode 100644 index 0000000000..a117e1b6dc --- /dev/null +++ b/sysdeps/aarch64/fpu/log1p_advsimd.c @@ -0,0 +1,129 @@ +/* Double-precision AdvSIMD log1p + + 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_f64.h" + +const static struct data +{ + float64x2_t poly[19], ln2[2]; + uint64x2_t hf_rt2_top, one_m_hf_rt2_top, umask, inf, minus_one; + int64x2_t one_top; +} data = { + /* Generated using Remez, deg=20, in [sqrt(2)/2-1, sqrt(2)-1]. */ + .poly = { V2 (-0x1.ffffffffffffbp-2), V2 (0x1.55555555551a9p-2), + V2 (-0x1.00000000008e3p-2), V2 (0x1.9999999a32797p-3), + V2 (-0x1.555555552fecfp-3), V2 (0x1.249248e071e5ap-3), + V2 (-0x1.ffffff8bf8482p-4), V2 (0x1.c71c8f07da57ap-4), + V2 (-0x1.9999ca4ccb617p-4), V2 (0x1.7459ad2e1dfa3p-4), + V2 (-0x1.554d2680a3ff2p-4), V2 (0x1.3b4c54d487455p-4), + V2 (-0x1.2548a9ffe80e6p-4), V2 (0x1.0f389a24b2e07p-4), + V2 (-0x1.eee4db15db335p-5), V2 (0x1.e95b494d4a5ddp-5), + V2 (-0x1.15fdf07cb7c73p-4), V2 (0x1.0310b70800fcfp-4), + V2 (-0x1.cfa7385bdb37ep-6) }, + .ln2 = { V2 (0x1.62e42fefa3800p-1), V2 (0x1.ef35793c76730p-45) }, + /* top32(asuint64(sqrt(2)/2)) << 32. */ + .hf_rt2_top = V2 (0x3fe6a09e00000000), + /* (top32(asuint64(1)) - top32(asuint64(sqrt(2)/2))) << 32. */ + .one_m_hf_rt2_top = V2 (0x00095f6200000000), + .umask = V2 (0x000fffff00000000), + .one_top = V2 (0x3ff), + .inf = V2 (0x7ff0000000000000), + .minus_one = V2 (0xbff0000000000000) +}; + +#define BottomMask v_u64 (0xffffffff) + +static float64x2_t VPCS_ATTR NOINLINE +special_case (float64x2_t x, float64x2_t y, uint64x2_t special) +{ + return v_call_f64 (log1p, x, y, special); +} + +/* Vector log1p approximation using polynomial on reduced interval. Routine is + a modification of the algorithm used in scalar log1p, with no shortcut for + k=0 and no narrowing for f and k. Maximum observed error is 2.45 ULP: + _ZGVnN2v_log1p(0x1.658f7035c4014p+11) got 0x1.fd61d0727429dp+2 + want 0x1.fd61d0727429fp+2 . */ +VPCS_ATTR float64x2_t V_NAME_D1 (log1p) (float64x2_t x) +{ + const struct data *d = ptr_barrier (&data); + uint64x2_t ix = vreinterpretq_u64_f64 (x); + uint64x2_t ia = vreinterpretq_u64_f64 (vabsq_f64 (x)); + uint64x2_t special = vcgeq_u64 (ia, d->inf); + +#if WANT_SIMD_EXCEPT + special = vorrq_u64 (special, + vcgeq_u64 (ix, vreinterpretq_u64_f64 (v_f64 (-1)))); + if (__glibc_unlikely (v_any_u64 (special))) + x = v_zerofy_f64 (x, special); +#else + special = vorrq_u64 (special, vcleq_f64 (x, v_f64 (-1))); +#endif + + /* With x + 1 = t * 2^k (where t = f + 1 and k is chosen such that f + is in [sqrt(2)/2, sqrt(2)]): + log1p(x) = k*log(2) + log1p(f). + + f may not be representable exactly, so we need a correction term: + let m = round(1 + x), c = (1 + x) - m. + c << m: at very small x, log1p(x) ~ x, hence: + log(1+x) - log(m) ~ c/m. + + We therefore calculate log1p(x) by k*log2 + log1p(f) + c/m. */ + + /* Obtain correctly scaled k by manipulation in the exponent. + The scalar algorithm casts down to 32-bit at this point to calculate k and + u_red. We stay in double-width to obtain f and k, using the same constants + as the scalar algorithm but shifted left by 32. */ + float64x2_t m = vaddq_f64 (x, v_f64 (1)); + uint64x2_t mi = vreinterpretq_u64_f64 (m); + uint64x2_t u = vaddq_u64 (mi, d->one_m_hf_rt2_top); + + int64x2_t ki + = vsubq_s64 (vreinterpretq_s64_u64 (vshrq_n_u64 (u, 52)), d->one_top); + float64x2_t k = vcvtq_f64_s64 (ki); + + /* Reduce x to f in [sqrt(2)/2, sqrt(2)]. */ + uint64x2_t utop = vaddq_u64 (vandq_u64 (u, d->umask), d->hf_rt2_top); + uint64x2_t u_red = vorrq_u64 (utop, vandq_u64 (mi, BottomMask)); + float64x2_t f = vsubq_f64 (vreinterpretq_f64_u64 (u_red), v_f64 (1)); + + /* Correction term c/m. */ + float64x2_t cm = vdivq_f64 (vsubq_f64 (x, vsubq_f64 (m, v_f64 (1))), m); + + /* Approximate log1p(x) on the reduced input using a polynomial. Because + log1p(0)=0 we choose an approximation of the form: + x + C0*x^2 + C1*x^3 + C2x^4 + ... + Hence approximation has the form f + f^2 * P(f) + where P(x) = C0 + C1*x + C2x^2 + ... + Assembling this all correctly is dealt with at the final step. */ + float64x2_t f2 = vmulq_f64 (f, f); + float64x2_t p = v_pw_horner_18_f64 (f, f2, d->poly); + + float64x2_t ylo = vfmaq_f64 (cm, k, d->ln2[1]); + float64x2_t yhi = vfmaq_f64 (f, k, d->ln2[0]); + float64x2_t y = vaddq_f64 (ylo, yhi); + + if (__glibc_unlikely (v_any_u64 (special))) + return special_case (vreinterpretq_f64_u64 (ix), vfmaq_f64 (y, f2, p), + special); + + return vfmaq_f64 (y, f2, p); +} |