1 files changed, 110 insertions, 0 deletions
diff --git a/pl/math/v_log10_2u5.c b/pl/math/v_log10_2u5.c
new file mode 100644
index 0000000..86d398c
--- /dev/null
+++ b/pl/math/v_log10_2u5.c
@@ -0,0 +1,110 @@
+/*
+ * Double-precision vector log10(x) function.
+ *
+ * Copyright (c) 2022-2023, Arm Limited.
+ * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
+ */
+
+#include "v_math.h"
+#include "include/mathlib.h"
+#include "pl_sig.h"
+#include "pl_test.h"
+
+#if V_SUPPORTED
+
+#define A(i) v_f64 (__v_log10_data.poly[i])
+#define T(s, i) __v_log10_data.tab[i].s
+#define Ln2 v_f64 (0x1.62e42fefa39efp-1)
+#define N (1 << V_LOG10_TABLE_BITS)
+#define OFF v_u64 (0x3fe6900900000000)
+
+struct entry
+{
+  v_f64_t invc;
+  v_f64_t log10c;
+};
+
+static inline struct entry
+lookup (v_u64_t i)
+{
+  struct entry e;
+#ifdef SCALAR
+  e.invc = T (invc, i);
+  e.log10c = T (log10c, i);
+#else
+  e.invc[0] = T (invc, i[0]);
+  e.log10c[0] = T (log10c, i[0]);
+  e.invc[1] = T (invc, i[1]);
+  e.log10c[1] = T (log10c, i[1]);
+#endif
+  return e;
+}
+
+VPCS_ATTR
+inline static v_f64_t
+specialcase (v_f64_t x, v_f64_t y, v_u64_t cmp)
+{
+  return v_call_f64 (log10, x, y, cmp);
+}
+
+/* Our implementation of v_log10 is a slight modification of v_log (1.660ulps).
+   Max ULP error: < 2.5 ulp (nearest rounding.)
+   Maximum measured at 2.46 ulp for x in [0.96, 0.97]
+     __v_log10(0x1.13192407fcb46p+0) got 0x1.fff6be3cae4bbp-6
+				    want 0x1.fff6be3cae4b9p-6
+     -0.459999 ulp err 1.96.  */
+VPCS_ATTR
+v_f64_t V_NAME (log10) (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_LOG10_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);
+
+  /* log10(x) = log1p(z/c-1)/log(10) + log10(c) + k*log10(2).  */
+  r = v_fma_f64 (z, e.invc, v_f64 (-1.0));
+  kd = v_to_f64_s64 (k);
+
+  /* hi = r / log(10) + log10(c) + k*log10(2).
+     Constants in `v_log10_data.c` are computed (in extended precision) as
+     e.log10c := e.logc * ivln10.  */
+  v_f64_t w = v_fma_f64 (r, v_f64 (__v_log10_data.invln10), e.log10c);
+
+  /* y = log10(1+r) + n * log10(2).  */
+  hi = v_fma_f64 (kd, v_f64 (__v_log10_data.log10_2), w);
+
+  /* y = r2*(A0 + r*A1 + r2*(A2 + r*A3 + r2*A4)) + hi.  */
+  r2 = r * r;
+  y = v_fma_f64 (A (3), r, A (2));
+  p = v_fma_f64 (A (1), r, A (0));
+  y = v_fma_f64 (A (4), 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
+
+PL_SIG (V, D, 1, log10, 0.01, 11.1)
+PL_TEST_ULP (V_NAME (log10), 1.97)
+PL_TEST_EXPECT_FENV_ALWAYS (V_NAME (log10))
+PL_TEST_INTERVAL (V_NAME (log10), 0, 0xffff000000000000, 10000)
+PL_TEST_INTERVAL (V_NAME (log10), 0x1p-4, 0x1p4, 400000)
+PL_TEST_INTERVAL (V_NAME (log10), 0, inf, 400000)
+#endif