1 files changed, 79 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/atanf_sve.c b/sysdeps/aarch64/fpu/atanf_sve.c
new file mode 100644
index 0000000000..9453e7aa29
--- /dev/null
+++ b/sysdeps/aarch64/fpu/atanf_sve.c
@@ -0,0 +1,79 @@
+/* Single-precision SVE inverse tan
+
+   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_f32.h"
+
+static const struct data
+{
+  float32_t poly[8];
+  float32_t pi_over_2;
+} data = {
+  /* Coefficients of polynomial P such that atan(x)~x+x*P(x^2) on
+    [2**-128, 1.0].  */
+  .poly = { -0x1.55555p-2f, 0x1.99935ep-3f, -0x1.24051ep-3f, 0x1.bd7368p-4f,
+	    -0x1.491f0ep-4f, 0x1.93a2c0p-5f, -0x1.4c3c60p-6f, 0x1.01fd88p-8f },
+  .pi_over_2 = 0x1.921fb6p+0f,
+};
+
+#define SignMask (0x80000000)
+
+/* Fast implementation of SVE atanf based on
+   atan(x) ~ shift + z + z^3 * P(z^2) with reduction to [0,1] using
+   z=-1/x and shift = pi/2.
+   Largest observed error is 2.9 ULP, close to +/-1.0:
+   _ZGVsMxv_atanf (0x1.0468f6p+0) got -0x1.967f06p-1
+				 want -0x1.967fp-1.  */
+svfloat32_t SV_NAME_F1 (atan) (svfloat32_t x, const svbool_t pg)
+{
+  const struct data *d = ptr_barrier (&data);
+
+  /* No need to trigger special case. Small cases, infs and nans
+     are supported by our approximation technique.  */
+  svuint32_t ix = svreinterpret_u32 (x);
+  svuint32_t sign = svand_x (pg, ix, SignMask);
+
+  /* Argument reduction:
+     y := arctan(x) for x < 1
+     y := pi/2 + arctan(-1/x) for x > 1
+     Hence, use z=-1/a if x>=1, otherwise z=a.  */
+  svbool_t red = svacgt (pg, x, 1.0f);
+  /* Avoid dependency in abs(x) in division (and comparison).  */
+  svfloat32_t z = svsel (red, svdiv_x (pg, sv_f32 (1.0f), x), x);
+  /* Use absolute value only when needed (odd powers of z).  */
+  svfloat32_t az = svabs_x (pg, z);
+  az = svneg_m (az, red, az);
+
+  /* Use split Estrin scheme for P(z^2) with deg(P)=7.  */
+  svfloat32_t z2 = svmul_x (pg, z, z);
+  svfloat32_t z4 = svmul_x (pg, z2, z2);
+  svfloat32_t z8 = svmul_x (pg, z4, z4);
+
+  svfloat32_t y = sv_estrin_7_f32_x (pg, z2, z4, z8, d->poly);
+
+  /* y = shift + z + z^3 * P(z^2).  */
+  svfloat32_t z3 = svmul_x (pg, z2, az);
+  y = svmla_x (pg, az, z3, y);
+
+  /* Apply shift as indicated by 'red' predicate.  */
+  y = svadd_m (red, y, sv_f32 (d->pi_over_2));
+
+  /* y = atan(x) if x>0, -atan(-x) otherwise.  */
+  return svreinterpret_f32 (sveor_x (pg, svreinterpret_u32 (y), sign));
+}