diff --git a/src/string_util.cc b/src/string_util.cc
new file mode 100644
index 0000000..05ac5b4
--- /dev/null
+++ b/src/string_util.cc
@@ -0,0 +1,261 @@
+#include "string_util.h"
+
+#include <array>
+#include <cmath>
+#include <cstdarg>
+#include <cstdio>
+#include <memory>
+#include <sstream>
+
+#include "arraysize.h"
+
+namespace benchmark {
+namespace {
+
+// kilo, Mega, Giga, Tera, Peta, Exa, Zetta, Yotta.
+const char kBigSIUnits[] = "kMGTPEZY";
+// Kibi, Mebi, Gibi, Tebi, Pebi, Exbi, Zebi, Yobi.
+const char kBigIECUnits[] = "KMGTPEZY";
+// milli, micro, nano, pico, femto, atto, zepto, yocto.
+const char kSmallSIUnits[] = "munpfazy";
+
+// We require that all three arrays have the same size.
+static_assert(arraysize(kBigSIUnits) == arraysize(kBigIECUnits),
+              "SI and IEC unit arrays must be the same size");
+static_assert(arraysize(kSmallSIUnits) == arraysize(kBigSIUnits),
+              "Small SI and Big SI unit arrays must be the same size");
+
+static const int64_t kUnitsSize = arraysize(kBigSIUnits);
+
+void ToExponentAndMantissa(double val, double thresh, int precision,
+                           double one_k, std::string* mantissa,
+                           int64_t* exponent) {
+  std::stringstream mantissa_stream;
+
+  if (val < 0) {
+    mantissa_stream << "-";
+    val = -val;
+  }
+
+  // Adjust threshold so that it never excludes things which can't be rendered
+  // in 'precision' digits.
+  const double adjusted_threshold =
+      std::max(thresh, 1.0 / std::pow(10.0, precision));
+  const double big_threshold = adjusted_threshold * one_k;
+  const double small_threshold = adjusted_threshold;
+  // Values in ]simple_threshold,small_threshold[ will be printed as-is
+  const double simple_threshold = 0.01;
+
+  if (val > big_threshold) {
+    // Positive powers
+    double scaled = val;
+    for (size_t i = 0; i < arraysize(kBigSIUnits); ++i) {
+      scaled /= one_k;
+      if (scaled <= big_threshold) {
+        mantissa_stream << scaled;
+        *exponent = i + 1;
+        *mantissa = mantissa_stream.str();
+        return;
+      }
+    }
+    mantissa_stream << val;
+    *exponent = 0;
+  } else if (val < small_threshold) {
+    // Negative powers
+    if (val < simple_threshold) {
+      double scaled = val;
+      for (size_t i = 0; i < arraysize(kSmallSIUnits); ++i) {
+        scaled *= one_k;
+        if (scaled >= small_threshold) {
+          mantissa_stream << scaled;
+          *exponent = -static_cast<int64_t>(i + 1);
+          *mantissa = mantissa_stream.str();
+          return;
+        }
+      }
+    }
+    mantissa_stream << val;
+    *exponent = 0;
+  } else {
+    mantissa_stream << val;
+    *exponent = 0;
+  }
+  *mantissa = mantissa_stream.str();
+}
+
+std::string ExponentToPrefix(int64_t exponent, bool iec) {
+  if (exponent == 0) return "";
+
+  const int64_t index = (exponent > 0 ? exponent - 1 : -exponent - 1);
+  if (index >= kUnitsSize) return "";
+
+  const char* array =
+      (exponent > 0 ? (iec ? kBigIECUnits : kBigSIUnits) : kSmallSIUnits);
+  if (iec)
+    return array[index] + std::string("i");
+  else
+    return std::string(1, array[index]);
+}
+
+std::string ToBinaryStringFullySpecified(double value, double threshold,
+                                         int precision, double one_k = 1024.0) {
+  std::string mantissa;
+  int64_t exponent;
+  ToExponentAndMantissa(value, threshold, precision, one_k, &mantissa,
+                        &exponent);
+  return mantissa + ExponentToPrefix(exponent, false);
+}
+
+}  // end namespace
+
+void AppendHumanReadable(int n, std::string* str) {
+  std::stringstream ss;
+  // Round down to the nearest SI prefix.
+  ss << ToBinaryStringFullySpecified(n, 1.0, 0);
+  *str += ss.str();
+}
+
+std::string HumanReadableNumber(double n, double one_k) {
+  // 1.1 means that figures up to 1.1k should be shown with the next unit down;
+  // this softens edge effects.
+  // 1 means that we should show one decimal place of precision.
+  return ToBinaryStringFullySpecified(n, 1.1, 1, one_k);
+}
+
+std::string StrFormatImp(const char* msg, va_list args) {
+  // we might need a second shot at this, so pre-emptivly make a copy
+  va_list args_cp;
+  va_copy(args_cp, args);
+
+  // TODO(ericwf): use std::array for first attempt to avoid one memory
+  // allocation guess what the size might be
+  std::array<char, 256> local_buff;
+  std::size_t size = local_buff.size();
+  // 2015-10-08: vsnprintf is used instead of snd::vsnprintf due to a limitation
+  // in the android-ndk
+  auto ret = vsnprintf(local_buff.data(), size, msg, args_cp);
+
+  va_end(args_cp);
+
+  // handle empty expansion
+  if (ret == 0) return std::string{};
+  if (static_cast<std::size_t>(ret) < size)
+    return std::string(local_buff.data());
+
+  // we did not provide a long enough buffer on our first attempt.
+  // add 1 to size to account for null-byte in size cast to prevent overflow
+  size = static_cast<std::size_t>(ret) + 1;
+  auto buff_ptr = std::unique_ptr<char[]>(new char[size]);
+  // 2015-10-08: vsnprintf is used instead of snd::vsnprintf due to a limitation
+  // in the android-ndk
+  ret = vsnprintf(buff_ptr.get(), size, msg, args);
+  return std::string(buff_ptr.get());
+}
+
+std::string StrFormat(const char* format, ...) {
+  va_list args;
+  va_start(args, format);
+  std::string tmp = StrFormatImp(format, args);
+  va_end(args);
+  return tmp;
+}
+
+void ReplaceAll(std::string* str, const std::string& from,
+                const std::string& to) {
+  std::size_t start = 0;
+  while ((start = str->find(from, start)) != std::string::npos) {
+    str->replace(start, from.length(), to);
+    start += to.length();
+  }
+}
+
+#ifdef BENCHMARK_STL_ANDROID_GNUSTL
+/*
+ * GNU STL in Android NDK lacks support for some C++11 functions, including
+ * stoul, stoi, stod. We reimplement them here using C functions strtoul,
+ * strtol, strtod. Note that reimplemented functions are in benchmark::
+ * namespace, not std:: namespace.
+ */
+unsigned long stoul(const std::string& str, size_t* pos, int base) {
+  /* Record previous errno */
+  const int oldErrno = errno;
+  errno = 0;
+
+  const char* strStart = str.c_str();
+  char* strEnd = const_cast<char*>(strStart);
+  const unsigned long result = strtoul(strStart, &strEnd, base);
+
+  const int strtoulErrno = errno;
+  /* Restore previous errno */
+  errno = oldErrno;
+
+  /* Check for errors and return */
+  if (strtoulErrno == ERANGE) {
+    throw std::out_of_range(
+      "stoul failed: " + str + " is outside of range of unsigned long");
+  } else if (strEnd == strStart || strtoulErrno != 0) {
+    throw std::invalid_argument(
+      "stoul failed: " + str + " is not an integer");
+  }
+  if (pos != nullptr) {
+    *pos = static_cast<size_t>(strEnd - strStart);
+  }
+  return result;
+}
+
+int stoi(const std::string& str, size_t* pos, int base) {
+  /* Record previous errno */
+  const int oldErrno = errno;
+  errno = 0;
+
+  const char* strStart = str.c_str();
+  char* strEnd = const_cast<char*>(strStart);
+  const long result = strtol(strStart, &strEnd, base);
+
+  const int strtolErrno = errno;
+  /* Restore previous errno */
+  errno = oldErrno;
+
+  /* Check for errors and return */
+  if (strtolErrno == ERANGE || long(int(result)) != result) {
+    throw std::out_of_range(
+      "stoul failed: " + str + " is outside of range of int");
+  } else if (strEnd == strStart || strtolErrno != 0) {
+    throw std::invalid_argument(
+      "stoul failed: " + str + " is not an integer");
+  }
+  if (pos != nullptr) {
+    *pos = static_cast<size_t>(strEnd - strStart);
+  }
+  return int(result);
+}
+
+double stod(const std::string& str, size_t* pos) {
+  /* Record previous errno */
+  const int oldErrno = errno;
+  errno = 0;
+
+  const char* strStart = str.c_str();
+  char* strEnd = const_cast<char*>(strStart);
+  const double result = strtod(strStart, &strEnd);
+
+  /* Restore previous errno */
+  const int strtodErrno = errno;
+  errno = oldErrno;
+
+  /* Check for errors and return */
+  if (strtodErrno == ERANGE) {
+    throw std::out_of_range(
+      "stoul failed: " + str + " is outside of range of int");
+  } else if (strEnd == strStart || strtodErrno != 0) {
+    throw std::invalid_argument(
+      "stoul failed: " + str + " is not an integer");
+  }
+  if (pos != nullptr) {
+    *pos = static_cast<size_t>(strEnd - strStart);
+  }
+  return result;
+}
+#endif
+
+}  // end namespace benchmark