TensorFlow: Initial commit of TensorFlow library.

TensorFlow is an open source software library for numerical computation
using data flow graphs.

Base CL: 107276108

1 files changed, 84 insertions, 0 deletions

diff --git a/tensorflow/core/lib/core/bits.h b/tensorflow/core/lib/core/bits.h
new file mode 100644
index 0000000000..5456a63168
--- /dev/null
+++ b/tensorflow/core/lib/core/bits.h
@@ -0,0 +1,84 @@
+#ifndef TENSORFLOW_LIB_CORE_BITS_H_
+#define TENSORFLOW_LIB_CORE_BITS_H_
+
+#include "tensorflow/core/platform/port.h"
+
+namespace tensorflow {
+
+// Return floor(log2(n)) for positive integer n.  Returns -1 iff n == 0.
+int Log2Floor(uint32 n);
+int Log2Floor64(uint64 n);
+
+// Return ceiling(log2(n)) for positive integer n.  Returns -1 iff n == 0.
+int Log2Ceiling(uint32 n);
+int Log2Ceiling64(uint64 n);
+
+// ------------------------------------------------------------------------
+// Implementation details follow
+// ------------------------------------------------------------------------
+
+#if defined(__GNUC__)
+
+// Return floor(log2(n)) for positive integer n.  Returns -1 iff n == 0.
+inline int Log2Floor(uint32 n) {
+  return n == 0 ? -1 : 31 ^ __builtin_clz(n);
+}
+
+// Return floor(log2(n)) for positive integer n.  Returns -1 iff n == 0.
+inline int Log2Floor64(uint64 n) {
+  return n == 0 ? -1 : 63 ^ __builtin_clzll(n);
+}
+
+#else
+
+// Return floor(log2(n)) for positive integer n.  Returns -1 iff n == 0.
+inline int Log2Floor(uint32 n) {
+  if (n == 0)
+    return -1;
+  int log = 0;
+  uint32 value = n;
+  for (int i = 4; i >= 0; --i) {
+    int shift = (1 << i);
+    uint32 x = value >> shift;
+    if (x != 0) {
+      value = x;
+      log += shift;
+    }
+  }
+  assert(value == 1);
+  return log;
+}
+
+// Return floor(log2(n)) for positive integer n.  Returns -1 iff n == 0.
+// Log2Floor64() is defined in terms of Log2Floor32()
+inline int Log2Floor64(uint64 n) {
+  const uint32 topbits = static_cast<uint32>(n >> 32);
+  if (topbits == 0) {
+    // Top bits are zero, so scan in bottom bits
+    return Log2Floor(static_cast<uint32>(n));
+  } else {
+    return 32 + Log2Floor(topbits);
+  }
+}
+
+#endif
+
+inline int Log2Ceiling(uint32 n) {
+  int floor = Log2Floor(n);
+  if (n == (n & ~(n - 1)))  // zero or a power of two
+    return floor;
+  else
+    return floor + 1;
+}
+
+inline int Log2Ceiling64(uint64 n) {
+  int floor = Log2Floor64(n);
+  if (n == (n & ~(n - 1)))  // zero or a power of two
+    return floor;
+  else
+    return floor + 1;
+}
+
+}  // namespace tensorflow
+
+#endif  // TENSORFLOW_LIB_CORE_BITS_H_