mirror of git://sourceware.org/git/glibc.git
69 lines
2.7 KiB
C
69 lines
2.7 KiB
C
/* Helper for single-precision AdvSIMD routines which depend on exp
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Copyright (C) 2024-2025 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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#ifndef AARCH64_FPU_V_EXPF_INLINE_H
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#define AARCH64_FPU_V_EXPF_INLINE_H
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#include "v_math.h"
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struct v_expf_data
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{
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float ln2_hi, ln2_lo, c0, c2;
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float32x4_t inv_ln2, c1, c3, c4;
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/* asuint(1.0f). */
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uint32x4_t exponent_bias;
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};
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/* maxerr: 1.45358 +0.5 ulp. */
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#define V_EXPF_DATA \
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{ \
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.c0 = 0x1.0e4020p-7f, .c1 = V4 (0x1.573e2ep-5f), .c2 = 0x1.555e66p-3f, \
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.c3 = V4 (0x1.fffdb6p-2f), .c4 = V4 (0x1.ffffecp-1f), \
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.ln2_hi = 0x1.62e4p-1f, .ln2_lo = 0x1.7f7d1cp-20f, \
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.inv_ln2 = V4 (0x1.715476p+0f), .exponent_bias = V4 (0x3f800000), \
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}
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static inline float32x4_t
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v_expf_inline (float32x4_t x, const struct v_expf_data *d)
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{
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/* Helper routine for calculating exp(ax).
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Copied from v_expf.c, with all special-case handling removed - the
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calling routine should handle special values if required. */
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/* exp(ax) = 2^n (1 + poly(r)), with 1 + poly(r) in [1/sqrt(2),sqrt(2)]
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ax = ln2*n + r, with r in [-ln2/2, ln2/2]. */
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float32x4_t ax = vabsq_f32 (x);
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float32x4_t ln2_c02 = vld1q_f32 (&d->ln2_hi);
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float32x4_t n = vrndaq_f32 (vmulq_f32 (ax, d->inv_ln2));
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float32x4_t r = vfmsq_laneq_f32 (ax, n, ln2_c02, 0);
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r = vfmsq_laneq_f32 (r, n, ln2_c02, 1);
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uint32x4_t e = vshlq_n_u32 (vreinterpretq_u32_s32 (vcvtq_s32_f32 (n)), 23);
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float32x4_t scale = vreinterpretq_f32_u32 (vaddq_u32 (e, d->exponent_bias));
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/* Custom order-4 Estrin avoids building high order monomial. */
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float32x4_t r2 = vmulq_f32 (r, r);
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float32x4_t p = vfmaq_laneq_f32 (d->c1, r, ln2_c02, 2);
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float32x4_t q = vfmaq_laneq_f32 (d->c3, r, ln2_c02, 3);
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q = vfmaq_f32 (q, p, r2);
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p = vmulq_f32 (d->c4, r);
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float32x4_t poly = vfmaq_f32 (p, q, r2);
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return vfmaq_f32 (scale, poly, scale);
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}
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#endif
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