1 files changed, 72 insertions, 0 deletions
diff --git a/math/aarch64/experimental/atanf_2u9.c b/math/aarch64/experimental/atanf_2u9.c
new file mode 100644
index 000000000000..518415ded634
--- /dev/null
+++ b/math/aarch64/experimental/atanf_2u9.c
@@ -0,0 +1,72 @@
+/*
+ * Single-precision atan(x) function.
+ *
+ * Copyright (c) 2022-2024, Arm Limited.
+ * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
+ */
+
+#include "atanf_common.h"
+#include "test_sig.h"
+#include "test_defs.h"
+
+#define PiOver2 0x1.921fb6p+0f
+#define AbsMask 0x7fffffff
+#define TinyBound 0x30800000 /* asuint(0x1p-30).  */
+#define BigBound 0x4e800000  /* asuint(0x1p30).  */
+#define One 0x3f800000
+
+/* Approximation of single-precision atan(x) based on
+   atan(x) ~ shift + z + z^3 * P(z^2) with reduction to [0,1]
+   using z=-1/x and shift = pi/2.
+   Maximum error is 2.88 ulps:
+   atanf(0x1.0565ccp+0) got 0x1.97771p-1
+		       want 0x1.97770ap-1.  */
+float
+atanf (float x)
+{
+  uint32_t ix = asuint (x);
+  uint32_t sign = ix & ~AbsMask;
+  uint32_t ia = ix & AbsMask;
+
+  if (unlikely (ia < TinyBound))
+    /* Avoid underflow by returning x.  */
+    return x;
+
+  if (unlikely (ia > BigBound))
+    {
+      if (ia > 0x7f800000)
+	/* Propagate NaN.  */
+	return __math_invalidf (x);
+      /* atan(x) rounds to PiOver2 for large x.  */
+      return asfloat (asuint (PiOver2) ^ sign);
+    }
+
+  float z, az, shift;
+  if (ia > One)
+    {
+      /* For x > 1, use atan(x) = pi / 2 + atan(-1 / x).  */
+      z = -1.0f / x;
+      shift = PiOver2;
+      /* Use absolute value only when needed (odd powers of z).  */
+      az = -fabsf (z);
+    }
+  else
+    {
+      /* For x < 1, approximate atan(x) directly.  */
+      z = x;
+      az = asfloat (ia);
+      shift = 0;
+    }
+
+  /* Calculate polynomial, shift + z + z^3 * P(z^2).  */
+  float y = eval_poly (z, az, shift);
+  /* Copy sign.  */
+  return asfloat (asuint (y) ^ sign);
+}
+
+TEST_SIG (S, F, 1, atan, -10.0, 10.0)
+TEST_ULP (atanf, 2.38)
+TEST_SYM_INTERVAL (atanf, 0, 0x1p-30, 5000)
+TEST_SYM_INTERVAL (atanf, 0x1p-30, 1, 40000)
+TEST_SYM_INTERVAL (atanf, 1, 0x1p30, 40000)
+TEST_SYM_INTERVAL (atanf, 0x1p30, inf, 1000)