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86 lines
3.0 KiB
C
86 lines
3.0 KiB
C
/* Single-precision vector (SVE) log function.
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Copyright (C) 2023-2024 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 "sv_math.h"
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static const struct data
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{
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float poly_0135[4];
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float poly_246[3];
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float ln2;
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} data = {
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.poly_0135 = {
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/* Coefficients copied from the AdvSIMD routine in math/, then rearranged so
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that coeffs 0, 1, 3 and 5 can be loaded as a single quad-word, hence used
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with _lane variant of MLA intrinsic. */
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-0x1.3e737cp-3f, 0x1.5a9aa2p-3f, 0x1.961348p-3f, 0x1.555d7cp-2f
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},
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.poly_246 = { -0x1.4f9934p-3f, -0x1.00187cp-2f, -0x1.ffffc8p-2f },
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.ln2 = 0x1.62e43p-1f
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};
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#define Min (0x00800000)
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#define Max (0x7f800000)
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#define Thresh (0x7f000000) /* Max - Min. */
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#define Mask (0x007fffff)
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#define Off (0x3f2aaaab) /* 0.666667. */
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static svfloat32_t NOINLINE
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special_case (svfloat32_t x, svfloat32_t y, svbool_t cmp)
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{
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return sv_call_f32 (logf, x, y, cmp);
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}
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/* Optimised implementation of SVE logf, using the same algorithm and
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polynomial as the AdvSIMD routine. Maximum error is 3.34 ULPs:
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SV_NAME_F1 (log)(0x1.557298p+0) got 0x1.26edecp-2
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want 0x1.26ede6p-2. */
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svfloat32_t SV_NAME_F1 (log) (svfloat32_t x, const svbool_t pg)
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{
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const struct data *d = ptr_barrier (&data);
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svuint32_t u = svreinterpret_u32 (x);
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svbool_t cmp = svcmpge (pg, svsub_x (pg, u, Min), Thresh);
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/* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */
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u = svsub_x (pg, u, Off);
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svfloat32_t n = svcvt_f32_x (
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pg, svasr_x (pg, svreinterpret_s32 (u), 23)); /* Sign-extend. */
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u = svand_x (pg, u, Mask);
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u = svadd_x (pg, u, Off);
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svfloat32_t r = svsub_x (pg, svreinterpret_f32 (u), 1.0f);
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/* y = log(1+r) + n*ln2. */
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svfloat32_t r2 = svmul_x (pg, r, r);
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/* n*ln2 + r + r2*(P6 + r*P5 + r2*(P4 + r*P3 + r2*(P2 + r*P1 + r2*P0))). */
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svfloat32_t p_0135 = svld1rq (svptrue_b32 (), &d->poly_0135[0]);
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svfloat32_t p = svmla_lane (sv_f32 (d->poly_246[0]), r, p_0135, 1);
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svfloat32_t q = svmla_lane (sv_f32 (d->poly_246[1]), r, p_0135, 2);
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svfloat32_t y = svmla_lane (sv_f32 (d->poly_246[2]), r, p_0135, 3);
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p = svmla_lane (p, r2, p_0135, 0);
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q = svmla_x (pg, q, r2, p);
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y = svmla_x (pg, y, r2, q);
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p = svmla_x (pg, r, n, d->ln2);
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if (__glibc_unlikely (svptest_any (pg, cmp)))
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return special_case (x, svmla_x (svnot_z (pg, cmp), p, r2, y), cmp);
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return svmla_x (pg, p, r2, y);
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}
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