1 files changed, 76 insertions, 0 deletions
diff --git a/third_party/aom/aom_ports/bitops.h b/third_party/aom/aom_ports/bitops.h
new file mode 100644
index 000000000..36f5bd487
--- /dev/null
+++ b/third_party/aom/aom_ports/bitops.h
@@ -0,0 +1,76 @@
+/*
+ * Copyright (c) 2016, Alliance for Open Media. All rights reserved
+ *
+ * This source code is subject to the terms of the BSD 2 Clause License and
+ * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
+ * was not distributed with this source code in the LICENSE file, you can
+ * obtain it at www.aomedia.org/license/software. If the Alliance for Open
+ * Media Patent License 1.0 was not distributed with this source code in the
+ * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
+ */
+
+#ifndef AOM_PORTS_BITOPS_H_
+#define AOM_PORTS_BITOPS_H_
+
+#include <assert.h>
+
+#include "aom_ports/msvc.h"
+
+#ifdef _MSC_VER
+#if defined(_M_X64) || defined(_M_IX86)
+#include <intrin.h>
+#define USE_MSC_INTRINSICS
+#endif
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// These versions of get_msb() are only valid when n != 0 because all
+// of the optimized versions are undefined when n == 0:
+// https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
+
+// use GNU builtins where available.
+#if defined(__GNUC__) && \
+    ((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4)
+static INLINE int get_msb(unsigned int n) {
+  assert(n != 0);
+  return 31 ^ __builtin_clz(n);
+}
+#elif defined(USE_MSC_INTRINSICS)
+#pragma intrinsic(_BitScanReverse)
+
+static INLINE int get_msb(unsigned int n) {
+  unsigned long first_set_bit;
+  assert(n != 0);
+  _BitScanReverse(&first_set_bit, n);
+  return first_set_bit;
+}
+#undef USE_MSC_INTRINSICS
+#else
+// Returns (int)floor(log2(n)). n must be > 0.
+static INLINE int get_msb(unsigned int n) {
+  int log = 0;
+  unsigned int value = n;
+  int i;
+
+  assert(n != 0);
+
+  for (i = 4; i >= 0; --i) {
+    const int shift = (1 << i);
+    const unsigned int x = value >> shift;
+    if (x != 0) {
+      value = x;
+      log += shift;
+    }
+  }
+  return log;
+}
+#endif
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // AOM_PORTS_BITOPS_H_