diff --git a/tools/bit/util.cpp b/tools/bit/util.cpp
new file mode 100644
index 0000000..fc93bcb
--- /dev/null
+++ b/tools/bit/util.cpp
@@ -0,0 +1,254 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "util.h"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <dirent.h>
+#include <string.h>
+#include <unistd.h>
+
+
+FileInfo::FileInfo()
+{
+    memset(this, 0, sizeof(FileInfo));
+}
+
+FileInfo::FileInfo(const FileInfo& that)
+{
+    memcpy(this, &that, sizeof(FileInfo));
+}
+
+FileInfo::FileInfo(const string& filename)
+{
+    struct stat st;
+    int err = stat(filename.c_str(), &st);
+    if (err != 0) {
+        memset(this, 0, sizeof(FileInfo));
+    } else {
+        exists = true;
+        mtime = st.st_mtime;
+        ctime = st.st_ctime;
+        size = st.st_size;
+    }
+}
+
+bool
+FileInfo::operator==(const FileInfo& that) const
+{
+    return exists == that.exists
+            && mtime == that.mtime
+            && ctime == that.ctime
+            && size == that.size;
+}
+
+bool
+FileInfo::operator!=(const FileInfo& that) const
+{
+    return exists != that.exists
+            || mtime != that.mtime
+            || ctime != that.ctime
+            || size != that.size;
+}
+
+FileInfo::~FileInfo()
+{
+}
+
+TrackedFile::TrackedFile()
+    :filename(),
+     fileInfo()
+{
+}
+
+TrackedFile::TrackedFile(const TrackedFile& that)
+{
+    filename = that.filename;
+    fileInfo = that.fileInfo;
+}
+
+TrackedFile::TrackedFile(const string& file)
+    :filename(file),
+     fileInfo(file)
+{
+}
+
+TrackedFile::~TrackedFile()
+{
+}
+
+bool
+TrackedFile::HasChanged() const
+{
+    FileInfo updated(filename);
+    return !updated.exists || fileInfo != updated;
+}
+
+void
+get_directory_contents(const string& name, map<string,FileInfo>* results)
+{
+    int err;
+    DIR* dir = opendir(name.c_str());
+    if (dir == NULL) {
+        return;
+    }
+
+    dirent* entry;
+    while ((entry = readdir(dir)) != NULL) {
+        if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0) {
+            continue;
+        }
+        if (entry->d_type == DT_DIR) {
+            string subdir = name + "/" + entry->d_name;
+            get_directory_contents(subdir, results);
+        } else if (entry->d_type == DT_LNK || entry->d_type == DT_REG) {
+            string filename(name + "/" + entry->d_name);
+            (*results)[filename] = FileInfo(filename);
+        }
+    }
+
+    closedir(dir);
+}
+
+bool
+directory_contents_differ(const map<string,FileInfo>& before, const map<string,FileInfo>& after)
+{
+    if (before.size() != after.size()) {
+        return true;
+    }
+    map<string,FileInfo>::const_iterator b = before.begin();
+    map<string,FileInfo>::const_iterator a = after.begin();
+    while (b != before.end() && a != after.end()) {
+        if (b->first != a->first) {
+            return true;
+        }
+        if (a->second != b->second) {
+            return true;
+        }
+        a++;
+        b++;
+    }
+    return false;
+}
+
+string
+escape_quotes(const char* str)
+{
+    string result;
+    while (*str) {
+        if (*str == '"') {
+            result += '\\';
+            result += '"';
+        } else {
+            result += *str;
+        }
+    }
+    return result;
+}
+
+string
+escape_for_commandline(const char* str)
+{
+    if (strchr(str, '"') != NULL || strchr(str, ' ') != NULL
+            || strchr(str, '\t') != NULL) {
+        return escape_quotes(str);
+    } else {
+        return str;
+    }
+}
+
+static bool
+spacechr(char c)
+{
+    return c == ' ' || c == '\t' || c == '\n' || c == '\r';
+}
+
+string
+trim(const string& str)
+{
+    const ssize_t N = (ssize_t)str.size();
+    ssize_t begin = 0;
+    while (begin < N && spacechr(str[begin])) {
+        begin++;
+    }
+    ssize_t end = N - 1;
+    while (end >= begin && spacechr(str[end])) {
+        end--;
+    }
+    return string(str, begin, end-begin+1);
+}
+
+bool
+starts_with(const string& str, const string& prefix)
+{
+    return str.compare(0, prefix.length(), prefix) == 0;
+}
+
+bool
+ends_with(const string& str, const string& suffix)
+{
+    if (str.length() < suffix.length()) {
+        return false;
+    } else {
+        return str.compare(str.length()-suffix.length(), suffix.length(), suffix) == 0;
+    }
+}
+
+void
+split_lines(vector<string>* result, const string& str)
+{
+    const int N = str.length();
+    int begin = 0;
+    int end = 0;
+    for (; end < N; end++) {
+        const char c = str[end];
+        if (c == '\r' || c == '\n') {
+            if (begin != end) {
+                result->push_back(string(str, begin, end-begin));
+            }
+            begin = end+1;
+        }
+    }
+    if (begin != end) {
+        result->push_back(string(str, begin, end-begin));
+    }
+}
+
+string
+read_file(const string& filename)
+{
+    FILE* file = fopen(filename.c_str(), "r");
+    if (file == NULL) {
+        return string();
+    }
+    
+    fseek(file, 0, SEEK_END);
+    int size = ftell(file);
+    fseek(file, 0, SEEK_SET);
+
+    char* buf = (char*)malloc(size);
+    fread(buf, 1, size, file);
+
+    string result(buf, size);
+
+    free(buf);
+    fclose(file);
+
+    return result;
+}
+
+