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92 lines
3.1 KiB
C
92 lines
3.1 KiB
C
/* Double-precision vector (SVE) cos 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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double inv_pio2, pio2_1, pio2_2, pio2_3, shift;
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} data = {
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/* Polynomial coefficients are hardwired in FTMAD instructions. */
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.inv_pio2 = 0x1.45f306dc9c882p-1,
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.pio2_1 = 0x1.921fb50000000p+0,
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.pio2_2 = 0x1.110b460000000p-26,
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.pio2_3 = 0x1.1a62633145c07p-54,
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/* Original shift used in AdvSIMD cos,
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plus a contribution to set the bit #0 of q
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as expected by trigonometric instructions. */
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.shift = 0x1.8000000000001p52
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};
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#define RangeVal 0x4160000000000000 /* asuint64 (0x1p23). */
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static svfloat64_t NOINLINE
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special_case (svfloat64_t x, svfloat64_t y, svbool_t oob)
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{
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return sv_call_f64 (cos, x, y, oob);
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}
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/* A fast SVE implementation of cos based on trigonometric
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instructions (FTMAD, FTSSEL, FTSMUL).
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Maximum measured error: 2.108 ULPs.
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SV_NAME_D1 (cos)(0x1.9b0ba158c98f3p+7) got -0x1.fddd4c65c7f07p-3
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want -0x1.fddd4c65c7f05p-3. */
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svfloat64_t SV_NAME_D1 (cos) (svfloat64_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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svfloat64_t r = svabs_x (pg, x);
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svbool_t oob = svcmpge (pg, svreinterpret_u64 (r), RangeVal);
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/* Load some constants in quad-word chunks to minimise memory access. */
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svbool_t ptrue = svptrue_b64 ();
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svfloat64_t invpio2_and_pio2_1 = svld1rq (ptrue, &d->inv_pio2);
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svfloat64_t pio2_23 = svld1rq (ptrue, &d->pio2_2);
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/* n = rint(|x|/(pi/2)). */
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svfloat64_t q = svmla_lane (sv_f64 (d->shift), r, invpio2_and_pio2_1, 0);
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svfloat64_t n = svsub_x (pg, q, d->shift);
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/* r = |x| - n*(pi/2) (range reduction into -pi/4 .. pi/4). */
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r = svmls_lane (r, n, invpio2_and_pio2_1, 1);
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r = svmls_lane (r, n, pio2_23, 0);
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r = svmls_lane (r, n, pio2_23, 1);
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/* cos(r) poly approx. */
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svfloat64_t r2 = svtsmul (r, svreinterpret_u64 (q));
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svfloat64_t y = sv_f64 (0.0);
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y = svtmad (y, r2, 7);
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y = svtmad (y, r2, 6);
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y = svtmad (y, r2, 5);
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y = svtmad (y, r2, 4);
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y = svtmad (y, r2, 3);
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y = svtmad (y, r2, 2);
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y = svtmad (y, r2, 1);
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y = svtmad (y, r2, 0);
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/* Final multiplicative factor: 1.0 or x depending on bit #0 of q. */
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svfloat64_t f = svtssel (r, svreinterpret_u64 (q));
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if (__glibc_unlikely (svptest_any (pg, oob)))
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return special_case (x, svmul_x (svnot_z (pg, oob), y, f), oob);
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/* Apply factor. */
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return svmul_x (pg, f, y);
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}
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