aarch64: Add vector implementations of log10 routines

A table is also added, which is shared between AdvSIMD and SVE log10.

1 files changed, 76 insertions, 0 deletions

diff --git a/sysdeps/aarch64/fpu/log10_sve.c b/sysdeps/aarch64/fpu/log10_sve.c
new file mode 100644
index 0000000000..91060ab4a2
--- /dev/null
+++ b/sysdeps/aarch64/fpu/log10_sve.c
@@ -0,0 +1,76 @@
+/* Double-precision vector (SVE) log10 function
+
+   Copyright (C) 2023 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"
+#include "poly_sve_f64.h"
+
+#define Min 0x0010000000000000
+#define Max 0x7ff0000000000000
+#define Thres 0x7fe0000000000000 /* Max - Min.  */
+#define Off 0x3fe6900900000000
+#define N (1 << V_LOG10_TABLE_BITS)
+
+static svfloat64_t NOINLINE
+special_case (svfloat64_t x, svfloat64_t y, svbool_t special)
+{
+  return sv_call_f64 (log10, x, y, special);
+}
+
+/* SVE log10 algorithm.
+   Maximum measured error is 2.46 ulps.
+   SV_NAME_D1 (log10)(0x1.131956cd4b627p+0) got 0x1.fffbdf6eaa669p-6
+					   want 0x1.fffbdf6eaa667p-6.  */
+svfloat64_t SV_NAME_D1 (log10) (svfloat64_t x, const svbool_t pg)
+{
+  svuint64_t ix = svreinterpret_u64 (x);
+  svbool_t special = svcmpge (pg, svsub_x (pg, ix, Min), Thres);
+
+  /* x = 2^k z; where z is in range [Off,2*Off) and exact.
+     The range is split into N subintervals.
+     The ith subinterval contains z and c is near its center.  */
+  svuint64_t tmp = svsub_x (pg, ix, Off);
+  svuint64_t i = svlsr_x (pg, tmp, 51 - V_LOG10_TABLE_BITS);
+  i = svand_x (pg, i, (N - 1) << 1);
+  svfloat64_t k = svcvt_f64_x (pg, svasr_x (pg, svreinterpret_s64 (tmp), 52));
+  svfloat64_t z = svreinterpret_f64 (
+      svsub_x (pg, ix, svand_x (pg, tmp, 0xfffULL << 52)));
+
+  /* log(x) = k*log(2) + log(c) + log(z/c).  */
+  svfloat64_t invc = svld1_gather_index (pg, &__v_log10_data.table[0].invc, i);
+  svfloat64_t logc
+      = svld1_gather_index (pg, &__v_log10_data.table[0].log10c, i);
+
+  /* We approximate log(z/c) with a polynomial P(x) ~= log(x + 1):
+     r = z/c - 1 (we look up precomputed 1/c)
+     log(z/c) ~= P(r).  */
+  svfloat64_t r = svmad_x (pg, invc, z, -1.0);
+
+  /* hi = log(c) + k*log(2).  */
+  svfloat64_t w = svmla_x (pg, logc, r, __v_log10_data.invln10);
+  svfloat64_t hi = svmla_x (pg, w, k, __v_log10_data.log10_2);
+
+  /* y = r2*(A0 + r*A1 + r2*(A2 + r*A3 + r2*A4)) + hi.  */
+  svfloat64_t r2 = svmul_x (pg, r, r);
+  svfloat64_t y = sv_pw_horner_4_f64_x (pg, r, r2, __v_log10_data.poly);
+
+  if (__glibc_unlikely (svptest_any (pg, special)))
+    return special_case (x, svmla_x (svnot_z (pg, special), hi, r2, y),
+			 special);
+  return svmla_x (pg, hi, r2, y);
+}