diff --git a/internal/ceres/file.cc b/internal/ceres/file.cc
new file mode 100644
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--- /dev/null
+++ b/internal/ceres/file.cc
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+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2015 Google Inc. All rights reserved.
+// http://ceres-solver.org/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: keir@google.com (Keir Mierle)
+//
+// Really simple file IO.
+
+#include "ceres/file.h"
+
+#include <cstdio>
+#include "glog/logging.h"
+
+namespace ceres {
+namespace internal {
+
+using std::string;
+
+void WriteStringToFileOrDie(const string &data, const string &filename) {
+  FILE* file_descriptor = fopen(filename.c_str(), "wb");
+  if (!file_descriptor) {
+    LOG(FATAL) << "Couldn't write to file: " << filename;
+  }
+  fwrite(data.c_str(), 1, data.size(), file_descriptor);
+  fclose(file_descriptor);
+}
+
+void ReadFileToStringOrDie(const string &filename, string *data) {
+  FILE* file_descriptor = fopen(filename.c_str(), "r");
+
+  if (!file_descriptor) {
+    LOG(FATAL) << "Couldn't read file: " << filename;
+  }
+
+  // Resize the input buffer appropriately.
+  fseek(file_descriptor, 0L, SEEK_END);
+  int num_bytes = ftell(file_descriptor);
+  data->resize(num_bytes);
+
+  // Read the data.
+  fseek(file_descriptor, 0L, SEEK_SET);
+  int num_read = fread(&((*data)[0]),
+                       sizeof((*data)[0]),
+                       num_bytes,
+                       file_descriptor);
+  if (num_read != num_bytes) {
+    LOG(FATAL) << "Couldn't read all of " << filename
+               << "expected bytes: " << num_bytes * sizeof((*data)[0])
+               << "actual bytes: " << num_read;
+  }
+  fclose(file_descriptor);
+}
+
+string JoinPath(const string& dirname, const string& basename) {
+#ifdef _WIN32
+    static const char separator = '\\';
+#else
+    static const char separator = '/';
+#endif  // _WIN32
+
+  if ((!basename.empty() && basename[0] == separator) || dirname.empty()) {
+    return basename;
+  } else if (dirname[dirname.size() - 1] == separator) {
+    return dirname + basename;
+  } else {
+    return dirname + string(&separator, 1) + basename;
+  }
+}
+
+}  // namespace internal
+}  // namespace ceres