1 files changed, 104 insertions, 0 deletions
diff --git a/math/v_log.c b/math/v_log.c
new file mode 100644
index 0000000..d84c740
--- /dev/null
+++ b/math/v_log.c
@@ -0,0 +1,104 @@
+/*
+ * Double-precision vector log(x) function.
+ *
+ * Copyright (c) 2019, Arm Limited.
+ * SPDX-License-Identifier: MIT
+ */
+
+#include "mathlib.h"
+#include "v_math.h"
+#include "v_log.h"
+#if V_SUPPORTED
+
+/* Worst-case error: 1.17 + 0.5 ulp.  */
+
+static const f64_t Poly[] = {
+  /* rel error: 0x1.6272e588p-56 in [ -0x1.fc1p-9 0x1.009p-8 ].  */
+  -0x1.ffffffffffff7p-2,
+   0x1.55555555170d4p-2,
+  -0x1.0000000399c27p-2,
+   0x1.999b2e90e94cap-3,
+  -0x1.554e550bd501ep-3,
+};
+
+#define A0 v_f64 (Poly[0])
+#define A1 v_f64 (Poly[1])
+#define A2 v_f64 (Poly[2])
+#define A3 v_f64 (Poly[3])
+#define A4 v_f64 (Poly[4])
+#define Ln2 v_f64 (0x1.62e42fefa39efp-1)
+#define N (1 << V_LOG_TABLE_BITS)
+#define OFF v_u64 (0x3fe6900900000000)
+
+struct entry
+{
+  v_f64_t invc;
+  v_f64_t logc;
+};
+
+static inline struct entry
+lookup (v_u64_t i)
+{
+  struct entry e;
+#ifdef SCALAR
+  e.invc = __v_log_data[i].invc;
+  e.logc = __v_log_data[i].logc;
+#else
+  e.invc[0] = __v_log_data[i[0]].invc;
+  e.logc[0] = __v_log_data[i[0]].logc;
+  e.invc[1] = __v_log_data[i[1]].invc;
+  e.logc[1] = __v_log_data[i[1]].logc;
+#endif
+  return e;
+}
+
+VPCS_ATTR
+__attribute__ ((noinline)) static v_f64_t
+specialcase (v_f64_t x, v_f64_t y, v_u64_t cmp)
+{
+  return v_call_f64 (log, x, y, cmp);
+}
+
+VPCS_ATTR
+v_f64_t
+V_NAME(log) (v_f64_t x)
+{
+  v_f64_t z, r, r2, p, y, kd, hi;
+  v_u64_t ix, iz, tmp, top, i, cmp;
+  v_s64_t k;
+  struct entry e;
+
+  ix = v_as_u64_f64 (x);
+  top = ix >> 48;
+  cmp = v_cond_u64 (top - v_u64 (0x0010) >= v_u64 (0x7ff0 - 0x0010));
+
+  /* x = 2^k z; where z is in range [OFF,2*OFF) and exact.
+     The range is split into N subintervals.
+     The ith subinterval contains z and c is near its center.  */
+  tmp = ix - OFF;
+  i = (tmp >> (52 - V_LOG_TABLE_BITS)) % N;
+  k = v_as_s64_u64 (tmp) >> 52; /* arithmetic shift */
+  iz = ix - (tmp & v_u64 (0xfffULL << 52));
+  z = v_as_f64_u64 (iz);
+  e = lookup (i);
+
+  /* log(x) = log1p(z/c-1) + log(c) + k*Ln2.  */
+  r = v_fma_f64 (z, e.invc, v_f64 (-1.0));
+  kd = v_to_f64_s64 (k);
+
+  /* hi = r + log(c) + k*Ln2.  */
+  hi = v_fma_f64 (kd, Ln2, e.logc + r);
+  /* y = r2*(A0 + r*A1 + r2*(A2 + r*A3 + r2*A4)) + hi.  */
+  r2 = r * r;
+  y = v_fma_f64 (A3, r, A2);
+  p = v_fma_f64 (A1, r, A0);
+  y = v_fma_f64 (A4, r2, y);
+  y = v_fma_f64 (y, r2, p);
+  y = v_fma_f64 (y, r2, hi);
+
+  if (unlikely (v_any_u64 (cmp)))
+    return specialcase (x, y, cmp);
+  return y;
+}
+VPCS_ALIAS
+#endif