diff --git a/internal/ceres/stringprintf.h b/internal/ceres/stringprintf.h
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+++ b/internal/ceres/stringprintf.h
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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: Sanjay Ghemawat
+//
+// Printf variants that place their output in a C++ string.
+//
+// Usage:
+//      string result = StringPrintf("%d %s\n", 10, "hello");
+//      SStringPrintf(&result, "%d %s\n", 10, "hello");
+//      StringAppendF(&result, "%d %s\n", 20, "there");
+
+#ifndef CERES_INTERNAL_STRINGPRINTF_H_
+#define CERES_INTERNAL_STRINGPRINTF_H_
+
+#include <cstdarg>
+#include <string>
+
+#include "ceres/internal/port.h"
+
+namespace ceres {
+namespace internal {
+
+#if (defined(__GNUC__) || defined(__clang__))
+// Tell the compiler to do printf format string checking if the compiler
+// supports it; see the 'format' attribute in
+// <http://gcc.gnu.org/onlinedocs/gcc-4.3.0/gcc/Function-Attributes.html>.
+//
+// N.B.: As the GCC manual states, "[s]ince non-static C++ methods
+// have an implicit 'this' argument, the arguments of such methods
+// should be counted from two, not one."
+#define CERES_PRINTF_ATTRIBUTE(string_index, first_to_check) \
+    __attribute__((__format__ (__printf__, string_index, first_to_check)))
+#define CERES_SCANF_ATTRIBUTE(string_index, first_to_check) \
+    __attribute__((__format__ (__scanf__, string_index, first_to_check)))
+#else
+#define CERES_PRINTF_ATTRIBUTE(string_index, first_to_check)
+#endif
+
+// Return a C++ string.
+extern std::string StringPrintf(const char* format, ...)
+    // Tell the compiler to do printf format string checking.
+    CERES_PRINTF_ATTRIBUTE(1, 2);
+
+// Store result into a supplied string and return it.
+extern const std::string& SStringPrintf(std::string* dst, const char* format, ...)
+    // Tell the compiler to do printf format string checking.
+    CERES_PRINTF_ATTRIBUTE(2, 3);
+
+// Append result to a supplied string.
+extern void StringAppendF(std::string* dst, const char* format, ...)
+    // Tell the compiler to do printf format string checking.
+    CERES_PRINTF_ATTRIBUTE(2, 3);
+
+// Lower-level routine that takes a va_list and appends to a specified string.
+// All other routines are just convenience wrappers around it.
+extern void StringAppendV(std::string* dst, const char* format, va_list ap);
+
+#undef CERES_PRINTF_ATTRIBUTE
+
+}  // namespace internal
+}  // namespace ceres
+
+#endif  // CERES_INTERNAL_STRINGPRINTF_H_