/* Single-precision vector (SVE) log function. Copyright (C) 2023-2024 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 . */ #include "sv_math.h" static const struct data { float poly_0135[4]; float poly_246[3]; float ln2; } data = { .poly_0135 = { /* Coefficients copied from the AdvSIMD routine in math/, then rearranged so that coeffs 0, 1, 3 and 5 can be loaded as a single quad-word, hence used with _lane variant of MLA intrinsic. */ -0x1.3e737cp-3f, 0x1.5a9aa2p-3f, 0x1.961348p-3f, 0x1.555d7cp-2f }, .poly_246 = { -0x1.4f9934p-3f, -0x1.00187cp-2f, -0x1.ffffc8p-2f }, .ln2 = 0x1.62e43p-1f }; #define Min (0x00800000) #define Max (0x7f800000) #define Thresh (0x7f000000) /* Max - Min. */ #define Mask (0x007fffff) #define Off (0x3f2aaaab) /* 0.666667. */ static svfloat32_t NOINLINE special_case (svfloat32_t x, svfloat32_t y, svbool_t cmp) { return sv_call_f32 (logf, x, y, cmp); } /* Optimised implementation of SVE logf, using the same algorithm and polynomial as the AdvSIMD routine. Maximum error is 3.34 ULPs: SV_NAME_F1 (log)(0x1.557298p+0) got 0x1.26edecp-2 want 0x1.26ede6p-2. */ svfloat32_t SV_NAME_F1 (log) (svfloat32_t x, const svbool_t pg) { const struct data *d = ptr_barrier (&data); svuint32_t u = svreinterpret_u32 (x); svbool_t cmp = svcmpge (pg, svsub_x (pg, u, Min), Thresh); /* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */ u = svsub_x (pg, u, Off); svfloat32_t n = svcvt_f32_x ( pg, svasr_x (pg, svreinterpret_s32 (u), 23)); /* Sign-extend. */ u = svand_x (pg, u, Mask); u = svadd_x (pg, u, Off); svfloat32_t r = svsub_x (pg, svreinterpret_f32 (u), 1.0f); /* y = log(1+r) + n*ln2. */ svfloat32_t r2 = svmul_x (pg, r, r); /* n*ln2 + r + r2*(P6 + r*P5 + r2*(P4 + r*P3 + r2*(P2 + r*P1 + r2*P0))). */ svfloat32_t p_0135 = svld1rq (svptrue_b32 (), &d->poly_0135[0]); svfloat32_t p = svmla_lane (sv_f32 (d->poly_246[0]), r, p_0135, 1); svfloat32_t q = svmla_lane (sv_f32 (d->poly_246[1]), r, p_0135, 2); svfloat32_t y = svmla_lane (sv_f32 (d->poly_246[2]), r, p_0135, 3); p = svmla_lane (p, r2, p_0135, 0); q = svmla_x (pg, q, r2, p); y = svmla_x (pg, y, r2, q); p = svmla_x (pg, r, n, d->ln2); if (__glibc_unlikely (svptest_any (pg, cmp))) return special_case (x, svmla_x (svnot_z (pg, cmp), p, r2, y), cmp); return svmla_x (pg, p, r2, y); }