1 files changed, 68 insertions, 0 deletions
diff --git a/pl/math/v_log2f_2u5.c b/pl/math/v_log2f_2u5.c
new file mode 100644
index 0000000..8f9241b
--- /dev/null
+++ b/pl/math/v_log2f_2u5.c
@@ -0,0 +1,68 @@
+/*
+ * Single-precision vector log2 function.
+ *
+ * Copyright (c) 2022-2023, Arm Limited.
+ * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
+ */
+
+#include "v_math.h"
+#include "pairwise_hornerf.h"
+#include "pl_sig.h"
+#include "pl_test.h"
+#if V_SUPPORTED
+
+#define C(i) v_f32 (__v_log2f_data.poly[i])
+
+#define Ln2 v_f32 (0x1.62e43p-1f) /* 0x3f317218 */
+#define Min v_u32 (0x00800000)
+#define Max v_u32 (0x7f800000)
+#define Mask v_u32 (0x007fffff)
+#define Off v_u32 (0x3f2aaaab) /* 0.666667 */
+
+VPCS_ATTR
+NOINLINE static v_f32_t
+specialcase (v_f32_t x, v_f32_t y, v_u32_t cmp)
+{
+  /* Fall back to scalar code.  */
+  return v_call_f32 (log2f, x, y, cmp);
+}
+
+/* Fast implementation for single precision log2,
+   relies on same argument reduction as Neon logf.
+   Maximum error: 2.48 ULPs
+   __v_log2f(0x1.558174p+0) got 0x1.a9be84p-2
+			   want 0x1.a9be8p-2.  */
+VPCS_ATTR
+v_f32_t V_NAME (log2f) (v_f32_t x)
+{
+  v_u32_t u = v_as_u32_f32 (x);
+  v_u32_t cmp = v_cond_u32 (u - Min >= Max - Min);
+
+  /* x = 2^n * (1+r), where 2/3 < 1+r < 4/3.  */
+  u -= Off;
+  v_f32_t n = v_to_f32_s32 (v_as_s32_u32 (u) >> 23); /* signextend.  */
+  u &= Mask;
+  u += Off;
+  v_f32_t r = v_as_f32_u32 (u) - v_f32 (1.0f);
+
+  /* y = log2(1+r) + n.  */
+  v_f32_t r2 = r * r;
+  v_f32_t p = PAIRWISE_HORNER_8 (r, r2, C);
+  v_f32_t y = v_fma_f32 (p, r, n);
+
+  if (unlikely (v_any_u32 (cmp)))
+    return specialcase (x, y, cmp);
+  return y;
+}
+VPCS_ALIAS
+
+PL_SIG (V, F, 1, log2, 0.01, 11.1)
+PL_TEST_ULP (V_NAME (log2f), 1.99)
+PL_TEST_EXPECT_FENV_ALWAYS (V_NAME (log2f))
+PL_TEST_INTERVAL (V_NAME (log2f), -0.0, -0x1p126, 100)
+PL_TEST_INTERVAL (V_NAME (log2f), 0x1p-149, 0x1p-126, 4000)
+PL_TEST_INTERVAL (V_NAME (log2f), 0x1p-126, 0x1p-23, 50000)
+PL_TEST_INTERVAL (V_NAME (log2f), 0x1p-23, 1.0, 50000)
+PL_TEST_INTERVAL (V_NAME (log2f), 1.0, 100, 50000)
+PL_TEST_INTERVAL (V_NAME (log2f), 100, inf, 50000)
+#endif