Integrate internal changes

1 files changed, 55 insertions, 0 deletions

diff --git a/src/google/protobuf/stubs/port.h b/src/google/protobuf/stubs/port.h
index d7f93b4c..376be5f7 100644
--- a/src/google/protobuf/stubs/port.h
+++ b/src/google/protobuf/stubs/port.h
@@ -327,6 +327,61 @@ static inline uint64 bswap_64(uint64 x) {
 #endif
 
 // ===================================================================
+// from google3/util/bits/bits.h
+
+class Bits {
+ public:
+  static uint32 Log2FloorNonZero(uint32 n) {
+#if defined(__GNUC__)
+  return 31 ^ __builtin_clz(n);
+#elif defined(COMPILER_MSVC) && defined(_M_IX86)
+  _asm {
+    bsr ebx, n
+    mov n, ebx
+  }
+  return n;
+#else
+  return Log2FloorNonZero_Portable(n);
+#endif
+  }
+
+  static uint64 Log2FloorNonZero64(uint64 n) {
+#if defined(__GNUC__)
+  return 63 ^ __builtin_clzll(n);
+#else
+  return Log2FloorNonZero64_Portable(n);
+#endif
+  }
+ private:
+  static int Log2FloorNonZero_Portable(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;
+  }
+
+  static int Log2FloorNonZero64_Portable(uint64 n) {
+    const uint32 topbits = static_cast<uint32>(n >> 32);
+    if (topbits == 0) {
+      // Top bits are zero, so scan in bottom bits
+      return Log2FloorNonZero(static_cast<uint32>(n));
+    } else {
+      return 32 + Log2FloorNonZero(topbits);
+    }
+  }
+};
+
+// ===================================================================
 // from google3/util/endian/endian.h
 LIBPROTOBUF_EXPORT uint32 ghtonl(uint32 x);