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5a4b6f8e4b
* Transpose table layout for improved memory access
* Use half-vector special comparisons for AdvSIMD
* Improve register use near special-case branches
- Due to the presence of a function call, return value would get
mov-d out of x0 in order to facilitate PCS. By moving the final
computation after the branch this can be avoided
Also change SVE routines to use overloaded intrinsics for readability.
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 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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