diff options
Diffstat (limited to 'sysdeps/aarch64/fpu/erfcf_sve.c')
| -rw-r--r-- | sysdeps/aarch64/fpu/erfcf_sve.c | 113 |
1 files changed, 113 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/erfcf_sve.c b/sysdeps/aarch64/fpu/erfcf_sve.c new file mode 100644 index 0000000000..48d1677eb4 --- /dev/null +++ b/sysdeps/aarch64/fpu/erfcf_sve.c @@ -0,0 +1,113 @@ +/* Single-precision vector (SVE) erfc function + + Copyright (C) 2024 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ + +#include "sv_math.h" + +static const struct data +{ + uint32_t off_idx, off_arr; + float max, shift; + float third, two_thirds, two_over_fifteen, two_over_five, tenth; +} data = { + /* Set an offset so the range of the index used for lookup is 644, and it can + be clamped using a saturated add. */ + .off_idx = 0xb7fffd7b, /* 0xffffffff - asuint(shift) - 644. */ + .off_arr = 0xfffffd7b, /* 0xffffffff - 644. */ + .max = 10.0625f, /* 644/64. */ + .shift = 0x1p17f, + .third = 0x1.555556p-2f, + .two_thirds = 0x1.555556p-1f, + .two_over_fifteen = 0x1.111112p-3f, + .two_over_five = -0x1.99999ap-2f, + .tenth = -0x1.99999ap-4f, +}; + +#define SignMask 0x80000000 +#define TableScale 0x28000000 /* 0x1p-47. */ + +/* Optimized single-precision vector erfcf(x). + Approximation based on series expansion near x rounded to + nearest multiple of 1/64. + Let d = x - r, and scale = 2 / sqrt(pi) * exp(-r^2). For x near r, + + erfc(x) ~ erfc(r) - scale * d * poly(r, d), with + + poly(r, d) = 1 - r d + (2/3 r^2 - 1/3) d^2 - r (1/3 r^2 - 1/2) d^3 + + (2/15 r^4 - 2/5 r^2 + 1/10) d^4 + + Values of erfc(r) and scale are read from lookup tables. Stored values + are scaled to avoid hitting the subnormal range. + + Note that for x < 0, erfc(x) = 2.0 - erfc(-x). + + Maximum error: 1.63 ULP (~1.0 ULP for x < 0.0). + _ZGVsMxv_erfcf(0x1.1dbf7ap+3) got 0x1.f51212p-120 + want 0x1.f51216p-120. */ +svfloat32_t SV_NAME_F1 (erfc) (svfloat32_t x, const svbool_t pg) +{ + const struct data *dat = ptr_barrier (&data); + + svfloat32_t a = svabs_x (pg, x); + + /* Clamp input at |x| <= 10.0 + 4/64. */ + a = svmin_x (pg, a, dat->max); + + /* Reduce x to the nearest multiple of 1/64. */ + svfloat32_t shift = sv_f32 (dat->shift); + svfloat32_t z = svadd_x (pg, a, shift); + + /* Saturate index for the NaN case. */ + svuint32_t i = svqadd (svreinterpret_u32 (z), dat->off_idx); + + /* Lookup erfc(r) and 2/sqrt(pi)*exp(-r^2) in tables. */ + i = svmul_x (pg, i, 2); + const float32_t *p = &__erfcf_data.tab[0].erfc - 2 * dat->off_arr; + svfloat32_t erfcr = svld1_gather_index (pg, p, i); + svfloat32_t scale = svld1_gather_index (pg, p + 1, i); + + /* erfc(x) ~ erfc(r) - scale * d * poly(r, d). */ + svfloat32_t r = svsub_x (pg, z, shift); + svfloat32_t d = svsub_x (pg, a, r); + svfloat32_t d2 = svmul_x (pg, d, d); + svfloat32_t r2 = svmul_x (pg, r, r); + + svfloat32_t coeffs = svld1rq (svptrue_b32 (), &dat->third); + svfloat32_t third = svdup_lane (coeffs, 0); + + svfloat32_t p1 = r; + svfloat32_t p2 = svmls_lane (third, r2, coeffs, 1); + svfloat32_t p3 = svmul_x (pg, r, svmla_lane (sv_f32 (-0.5), r2, coeffs, 0)); + svfloat32_t p4 = svmla_lane (sv_f32 (dat->two_over_five), r2, coeffs, 2); + p4 = svmls_x (pg, sv_f32 (dat->tenth), r2, p4); + + svfloat32_t y = svmla_x (pg, p3, d, p4); + y = svmla_x (pg, p2, d, y); + y = svmla_x (pg, p1, d, y); + + /* Solves the |x| = inf/nan case. */ + y = svmls_x (pg, erfcr, scale, svmls_x (pg, d, d2, y)); + + /* Offset equals 2.0f if sign, else 0.0f. */ + svuint32_t sign = svand_x (pg, svreinterpret_u32 (x), SignMask); + svfloat32_t off = svreinterpret_f32 (svlsr_x (pg, sign, 1)); + /* Handle sign and scale back in a single fma. */ + svfloat32_t fac = svreinterpret_f32 (svorr_x (pg, sign, TableScale)); + + return svmla_x (pg, off, fac, y); +} |