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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>
65 lines
2.3 KiB
C
65 lines
2.3 KiB
C
/* Single-precision vector (SVE) cosh function
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Copyright (C) 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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static const struct data
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{
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struct sv_expf_data expf_consts;
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float special_bound;
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} data = {
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.expf_consts = SV_EXPF_DATA,
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/* 0x1.5a92d8p+6: expf overflows above this, so have to use special case. */
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.special_bound = 0x1.5a92d8p+6,
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};
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static svfloat32_t NOINLINE
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special_case (svfloat32_t x, svfloat32_t half_e, svfloat32_t half_over_e,
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svbool_t pg)
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{
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return sv_call_f32 (coshf, x, svadd_x (svptrue_b32 (), half_e, half_over_e),
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pg);
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}
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/* Single-precision vector cosh, using vector expf.
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Maximum error is 2.77 ULP:
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_ZGVsMxv_coshf(-0x1.5b38f4p+1) got 0x1.e45946p+2
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want 0x1.e4594cp+2. */
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svfloat32_t SV_NAME_F1 (cosh) (svfloat32_t x, svbool_t pg)
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{
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const struct data *d = ptr_barrier (&data);
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svbool_t special = svacge (pg, x, d->special_bound);
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/* Calculate cosh by exp(x) / 2 + exp(-x) / 2.
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Note that x is passed to exp here, rather than |x|. This is to avoid using
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destructive unary ABS for better register usage. However it means the
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routine is not exactly symmetrical, as the exp helper is slightly less
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accurate in the negative range. */
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svfloat32_t e = expf_inline (x, pg, &d->expf_consts);
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svfloat32_t half_e = svmul_x (svptrue_b32 (), e, 0.5);
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svfloat32_t half_over_e = svdivr_x (pg, e, 0.5);
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if (__glibc_unlikely (svptest_any (pg, special)))
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return special_case (x, half_e, half_over_e, special);
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return svadd_x (svptrue_b32 (), half_e, half_over_e);
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}
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