1 files changed, 76 insertions, 0 deletions
diff --git a/pl/math/expf.c b/pl/math/expf.c
new file mode 100644
index 0000000..c325e45
--- /dev/null
+++ b/pl/math/expf.c
@@ -0,0 +1,76 @@
+/*
+ * Single-precision e^x function.
+ *
+ * Copyright (c) 2017-2023, Arm Limited.
+ * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
+ */
+
+#include <math.h>
+#include <stdint.h>
+#include "math_config.h"
+
+/*
+EXPF_TABLE_BITS = 5
+EXPF_POLY_ORDER = 3
+
+ULP error: 0.502 (nearest rounding.)
+Relative error: 1.69 * 2^-34 in [-ln2/64, ln2/64] (before rounding.)
+Wrong count: 170635 (all nearest rounding wrong results with fma.)
+Non-nearest ULP error: 1 (rounded ULP error)
+*/
+
+#define N (1 << EXPF_TABLE_BITS)
+#define InvLn2N __expf_data.invln2_scaled
+#define T __expf_data.tab
+#define C __expf_data.poly_scaled
+
+static inline uint32_t
+top12 (float x)
+{
+  return asuint (x) >> 20;
+}
+
+float
+optr_aor_exp_f32 (float x)
+{
+  uint32_t abstop;
+  uint64_t ki, t;
+  /* double_t for better performance on targets with FLT_EVAL_METHOD==2.  */
+  double_t kd, xd, z, r, r2, y, s;
+
+  xd = (double_t) x;
+  abstop = top12 (x) & 0x7ff;
+  if (unlikely (abstop >= top12 (88.0f)))
+    {
+      /* |x| >= 88 or x is nan.  */
+      if (asuint (x) == asuint (-INFINITY))
+	return 0.0f;
+      if (abstop >= top12 (INFINITY))
+	return x + x;
+      if (x > 0x1.62e42ep6f) /* x > log(0x1p128) ~= 88.72 */
+	return __math_oflowf (0);
+      if (x < -0x1.9fe368p6f) /* x < log(0x1p-150) ~= -103.97 */
+	return __math_uflowf (0);
+    }
+
+  /* x*N/Ln2 = k + r with r in [-1/2, 1/2] and int k.  */
+  z = InvLn2N * xd;
+
+  /* Round and convert z to int, the result is in [-150*N, 128*N] and
+     ideally nearest int is used, otherwise the magnitude of r can be
+     bigger which gives larger approximation error.  */
+  kd = roundtoint (z);
+  ki = converttoint (z);
+  r = z - kd;
+
+  /* exp(x) = 2^(k/N) * 2^(r/N) ~= s * (C0*r^3 + C1*r^2 + C2*r + 1) */
+  t = T[ki % N];
+  t += ki << (52 - EXPF_TABLE_BITS);
+  s = asdouble (t);
+  z = C[0] * r + C[1];
+  r2 = r * r;
+  y = C[2] * r + 1;
+  y = z * r2 + y;
+  y = y * s;
+  return eval_as_float (y);
+}