1 files changed, 75 insertions, 0 deletions
diff --git a/pl/math/v_exp_tail.c b/pl/math/v_exp_tail.c
new file mode 100644
index 0000000..fd38aa8
--- /dev/null
+++ b/pl/math/v_exp_tail.c
@@ -0,0 +1,75 @@
+/*
+ * Double-precision vector e^(x+tail) function.
+ *
+ * Copyright (c) 2019-2023, Arm Limited.
+ * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
+ */
+
+#include "v_math.h"
+#include "math_config.h"
+#if V_SUPPORTED
+#include "v_exp_tail.h"
+
+#define C1 v_f64 (C1_scal)
+#define C2 v_f64 (C2_scal)
+#define C3 v_f64 (C3_scal)
+#define InvLn2 v_f64 (InvLn2_scal)
+#define Ln2hi v_f64 (Ln2hi_scal)
+#define Ln2lo v_f64 (Ln2lo_scal)
+
+#define IndexMask v_u64 (IndexMask_scal)
+#define Shift v_f64 (Shift_scal)
+#define Thres v_f64 (Thres_scal)
+
+VPCS_ATTR
+static v_f64_t
+specialcase (v_f64_t s, v_f64_t y, v_f64_t n)
+{
+  v_f64_t absn = v_abs_f64 (n);
+
+  /* 2^(n/N) may overflow, break it up into s1*s2.  */
+  v_u64_t b = v_cond_u64 (n <= v_f64 (0.0)) & v_u64 (0x6000000000000000);
+  v_f64_t s1 = v_as_f64_u64 (v_u64 (0x7000000000000000) - b);
+  v_f64_t s2 = v_as_f64_u64 (v_as_u64_f64 (s) - v_u64 (0x3010000000000000) + b);
+  v_u64_t cmp = v_cond_u64 (absn > v_f64 (1280.0 * N));
+  v_f64_t r1 = s1 * s1;
+  v_f64_t r0 = v_fma_f64 (y, s2, s2) * s1;
+  return v_as_f64_u64 ((cmp & v_as_u64_f64 (r1)) | (~cmp & v_as_u64_f64 (r0)));
+}
+
+VPCS_ATTR
+v_f64_t V_NAME (exp_tail) (v_f64_t x, v_f64_t xtail)
+{
+  v_f64_t n, r, s, y, z;
+  v_u64_t cmp, u, e, i;
+
+  cmp = v_cond_u64 (v_abs_f64 (x) > Thres);
+
+  /* n = round(x/(ln2/N)).  */
+  z = v_fma_f64 (x, InvLn2, Shift);
+  u = v_as_u64_f64 (z);
+  n = z - Shift;
+
+  /* r = x - n*ln2/N.  */
+  r = x;
+  r = v_fma_f64 (-Ln2hi, n, r);
+  r = v_fma_f64 (-Ln2lo, n, r);
+
+  e = u << (52 - V_EXP_TAIL_TABLE_BITS);
+  i = u & IndexMask;
+
+  /* y = tail + exp(r) - 1 ~= r + C1 r^2 + C2 r^3 + C3 r^4.  */
+  y = v_fma_f64 (C3, r, C2);
+  y = v_fma_f64 (y, r, C1);
+  y = v_fma_f64 (y, r, v_f64 (1.0));
+  y = v_fma_f64 (y, r, xtail);
+
+  /* s = 2^(n/N).  */
+  u = v_lookup_u64 (Tab, i);
+  s = v_as_f64_u64 (u + e);
+
+  if (unlikely (v_any_u64 (cmp)))
+    return specialcase (s, y, n);
+  return v_fma_f64 (y, s, s);
+}
+#endif