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86 lines
3.0 KiB
C
86 lines
3.0 KiB
C
/* Single-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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float neg_pio2_1, neg_pio2_2, neg_pio2_3, inv_pio2, shift;
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} data = {
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/* Polynomial coefficients are hard-wired in FTMAD instructions. */
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.neg_pio2_1 = -0x1.921fb6p+0f,
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.neg_pio2_2 = 0x1.777a5cp-25f,
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.neg_pio2_3 = 0x1.ee59dap-50f,
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.inv_pio2 = 0x1.45f306p-1f,
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/* Original shift used in AdvSIMD cosf,
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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 = 0x1.800002p+23f
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};
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#define RangeVal 0x49800000 /* asuint32(0x1p20f). */
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static svfloat32_t NOINLINE
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special_case (svfloat32_t x, svfloat32_t y, svbool_t oob)
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{
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return sv_call_f32 (cosf, x, y, oob);
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}
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/* A fast SVE implementation of cosf based on trigonometric
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instructions (FTMAD, FTSSEL, FTSMUL).
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Maximum measured error: 2.06 ULPs.
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SV_NAME_F1 (cos)(0x1.dea2f2p+19) got 0x1.fffe7ap-6
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want 0x1.fffe76p-6. */
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svfloat32_t SV_NAME_F1 (cos) (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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svfloat32_t r = svabs_x (pg, x);
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svbool_t oob = svcmpge (pg, svreinterpret_u32 (r), RangeVal);
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/* Load some constants in quad-word chunks to minimise memory access. */
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svfloat32_t negpio2_and_invpio2 = svld1rq (svptrue_b32 (), &d->neg_pio2_1);
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/* n = rint(|x|/(pi/2)). */
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svfloat32_t q = svmla_lane (sv_f32 (d->shift), r, negpio2_and_invpio2, 3);
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svfloat32_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 = svmla_lane (r, n, negpio2_and_invpio2, 0);
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r = svmla_lane (r, n, negpio2_and_invpio2, 1);
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r = svmla_lane (r, n, negpio2_and_invpio2, 2);
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/* Final multiplicative factor: 1.0 or x depending on bit #0 of q. */
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svfloat32_t f = svtssel (r, svreinterpret_u32 (q));
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/* cos(r) poly approx. */
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svfloat32_t r2 = svtsmul (r, svreinterpret_u32 (q));
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svfloat32_t y = sv_f32 (0.0f);
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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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if (__glibc_unlikely (svptest_any (pg, oob)))
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return special_case (x, svmul_x (svnot_z (pg, oob), f, y), 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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