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7b8c134b54
Reduce MOV and MOVPRFX by improving special-case handling. Use inline helper to duplicate the entire computation between the special- and non-special case branches, removing the contention for z0 between x and the return value. Also rearrange some MLAs and MLSs - by making the multiplicand the destination we can avoid a MOVPRFX in several cases. Also change which constants go in the vector used for lanewise ops - the last lane is no longer wasted. Spotted that shift was incorrect in exp2f and exp10f, w.r.t. to the comment that explains it. Fixed - worst-case ULP for exp2f moves around but it doesn't change significantly for either routine. Worst-case error for coshf increases due to passing x to exp rather than abs(x) - updated the comment, but does not require regen-ulps. Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
54 lines
1.8 KiB
C
54 lines
1.8 KiB
C
/* Single-precision vector (SVE) exp 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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#include "sv_expf_inline.h"
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/* Roughly 87.3. For x < -Thres, the result is subnormal and not handled
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correctly by FEXPA. */
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#define Thres 0x1.5d5e2ap+6f
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static const struct data
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{
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struct sv_expf_data d;
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float thres;
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} data = {
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.d = SV_EXPF_DATA,
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.thres = Thres,
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};
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static svfloat32_t NOINLINE
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special_case (svfloat32_t x, svbool_t special, const struct sv_expf_data *d)
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{
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return sv_call_f32 (expf, x, expf_inline (x, svptrue_b32 (), d), special);
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}
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/* Optimised single-precision SVE exp function.
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Worst-case error is 1.04 ulp:
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SV_NAME_F1 (exp)(0x1.a8eda4p+1) got 0x1.ba74bcp+4
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want 0x1.ba74bap+4. */
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svfloat32_t SV_NAME_F1 (exp) (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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svbool_t is_special_case = svacgt (pg, x, d->thres);
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if (__glibc_unlikely (svptest_any (pg, is_special_case)))
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return special_case (x, is_special_case, &d->d);
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return expf_inline (x, pg, &d->d);
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}
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