1 files changed, 79 insertions, 0 deletions
diff --git a/pl/math/sv_exp_tail.h b/pl/math/sv_exp_tail.h
new file mode 100644
index 0000000..9b739da
--- /dev/null
+++ b/pl/math/sv_exp_tail.h
@@ -0,0 +1,79 @@
+/*
+ * Double-precision SVE e^(x+tail) function.
+ *
+ * Copyright (c) 2021-2023, Arm Limited.
+ * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
+ */
+
+#ifndef SV_EXP_TAIL_H
+#define SV_EXP_TAIL_H
+
+#include "sv_math.h"
+#if SV_SUPPORTED
+
+#include "v_exp_tail.h"
+
+#define C1 sv_f64 (C1_scal)
+#define C2 sv_f64 (C2_scal)
+#define C3 sv_f64 (C3_scal)
+#define MinusLn2hi (-Ln2hi_scal)
+#define MinusLn2lo (-Ln2lo_scal)
+
+#define N (1 << V_EXP_TAIL_TABLE_BITS)
+#define Tab __v_exp_tail_data
+#define IndexMask (N - 1)
+#define Shift sv_f64 (0x1.8p+52)
+#define Thres 704.0
+
+static inline sv_f64_t
+sv_exp_tail_special_case (svbool_t pg, sv_f64_t s, sv_f64_t y, sv_f64_t n)
+{
+  sv_f64_t absn = svabs_f64_x (pg, n);
+
+  /* 2^(n/N) may overflow, break it up into s1*s2.  */
+  sv_u64_t b = svsel_u64 (svcmple_n_f64 (pg, n, 0), sv_u64 (0x6000000000000000),
+			  sv_u64 (0));
+  sv_f64_t s1 = sv_as_f64_u64 (svsubr_n_u64_x (pg, b, 0x7000000000000000));
+  sv_f64_t s2 = sv_as_f64_u64 (
+    svadd_u64_x (pg, svsub_n_u64_x (pg, sv_as_u64_f64 (s), 0x3010000000000000),
+		 b));
+
+  svbool_t cmp = svcmpgt_n_f64 (pg, absn, 1280.0 * N);
+  sv_f64_t r1 = svmul_f64_x (pg, s1, s1);
+  sv_f64_t r0 = svmul_f64_x (pg, sv_fma_f64_x (pg, y, s2, s2), s1);
+  return svsel_f64 (cmp, r1, r0);
+}
+
+static inline sv_f64_t
+sv_exp_tail (const svbool_t pg, sv_f64_t x, sv_f64_t xtail)
+{
+  /* Calculate exp(x + xtail).  */
+  sv_f64_t z = sv_fma_n_f64_x (pg, InvLn2_scal, x, Shift);
+  sv_f64_t n = svsub_f64_x (pg, z, Shift);
+
+  sv_f64_t r = sv_fma_n_f64_x (pg, MinusLn2hi, n, x);
+  r = sv_fma_n_f64_x (pg, MinusLn2lo, n, r);
+
+  sv_u64_t u = sv_as_u64_f64 (z);
+  sv_u64_t e = svlsl_n_u64_x (pg, u, 52 - V_EXP_TAIL_TABLE_BITS);
+  sv_u64_t i = svand_n_u64_x (pg, u, IndexMask);
+
+  sv_f64_t y = sv_fma_f64_x (pg, C3, r, C2);
+  y = sv_fma_f64_x (pg, y, r, C1);
+  y = sv_fma_f64_x (pg, y, r, sv_f64 (1.0));
+  y = sv_fma_f64_x (pg, y, r, xtail);
+
+  /* s = 2^(n/N).  */
+  u = sv_lookup_u64_x (pg, Tab, i);
+  sv_f64_t s = sv_as_f64_u64 (svadd_u64_x (pg, u, e));
+
+  svbool_t cmp = svcmpgt_n_f64 (pg, svabs_f64_x (pg, x), Thres);
+  if (unlikely (svptest_any (pg, cmp)))
+    {
+      return sv_exp_tail_special_case (pg, s, y, n);
+    }
+  return sv_fma_f64_x (pg, y, s, s);
+}
+
+#endif
+#endif