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+//
+// Copyright 2017 The Abseil Authors.
+//
+// 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.
+//
+// -----------------------------------------------------------------------------
+// File: numbers.h
+// -----------------------------------------------------------------------------
+//
+// This package contains functions for converting strings to numbers. For
+// converting numbers to strings, use `StrCat()` or `StrAppend()` in str_cat.h,
+// which automatically detect and convert most number values appropriately.
+
+#ifndef ABSL_STRINGS_NUMBERS_H_
+#define ABSL_STRINGS_NUMBERS_H_
+
+#include <cstddef>
+#include <cstdlib>
+#include <cstring>
+#include <ctime>
+#include <limits>
+#include <string>
+#include <type_traits>
+
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+#include "absl/numeric/int128.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+
+// SimpleAtoi()
+//
+// Converts the given std::string into an integer value, returning `true` if
+// successful. The std::string must reflect a base-10 integer (optionally followed or
+// preceded by ASCII whitespace) whose value falls within the range of the
+// integer type,
+template <typename int_type>
+ABSL_MUST_USE_RESULT bool SimpleAtoi(absl::string_view s, int_type* out);
+
+// SimpleAtof()
+//
+// Converts the given std::string (optionally followed or preceded by ASCII
+// whitespace) into a float, which may be rounded on overflow or underflow.
+ABSL_MUST_USE_RESULT bool SimpleAtof(absl::string_view str, float* value);
+
+// SimpleAtod()
+//
+// Converts the given std::string (optionally followed or preceded by ASCII
+// whitespace) into a double, which may be rounded on overflow or underflow.
+ABSL_MUST_USE_RESULT bool SimpleAtod(absl::string_view str, double* value);
+
+// SimpleAtob()
+//
+// Converts the given std::string into into a boolean, returning `true` if
+// successful. The following case-insensitive strings are interpreted as boolean
+// `true`: "true", "t", "yes", "y", "1". The following case-insensitive strings
+// are interpreted as boolean `false`: "false", "f", "no", "n", "0".
+ABSL_MUST_USE_RESULT bool SimpleAtob(absl::string_view str, bool* value);
+
+}  // namespace absl
+
+// End of public API.  Implementation details follow.
+
+namespace absl {
+namespace numbers_internal {
+
+// safe_strto?() functions for implementing SimpleAtoi()
+bool safe_strto32_base(absl::string_view text, int32_t* value, int base);
+bool safe_strto64_base(absl::string_view text, int64_t* value, int base);
+bool safe_strtou32_base(absl::string_view text, uint32_t* value, int base);
+bool safe_strtou64_base(absl::string_view text, uint64_t* value, int base);
+
+// These functions are intended for speed. All functions take an output buffer
+// as an argument and return a pointer to the last byte they wrote, which is the
+// terminating '\0'. At most `kFastToBufferSize` bytes are written.
+char* FastInt32ToBuffer(int32_t i, char* buffer);
+char* FastUInt32ToBuffer(uint32_t i, char* buffer);
+char* FastInt64ToBuffer(int64_t i, char* buffer);
+char* FastUInt64ToBuffer(uint64_t i, char* buffer);
+
+static const int kFastToBufferSize = 32;
+static const int kSixDigitsToBufferSize = 16;
+
+char* RoundTripDoubleToBuffer(double d, char* buffer);
+char* RoundTripFloatToBuffer(float f, char* buffer);
+
+// Helper function for fast formatting of floating-point values.
+// The result is the same as printf's "%g", a.k.a. "%.6g"; that is, six
+// significant digits are returned, trailing zeros are removed, and numbers
+// outside the range 0.0001-999999 are output using scientific notation
+// (1.23456e+06). This routine is heavily optimized.
+// Required buffer size is `kSixDigitsToBufferSize`.
+size_t SixDigitsToBuffer(double d, char* buffer);
+
+template <typename int_type>
+char* FastIntToBuffer(int_type i, char* buffer) {
+  static_assert(sizeof(i) <= 64 / 8,
+                "FastIntToBuffer works only with 64-bit-or-less integers.");
+  // TODO(jorg): This signed-ness check is used because it works correctly
+  // with enums, and it also serves to check that int_type is not a pointer.
+  // If one day something like std::is_signed<enum E> works, switch to it.
+  if (static_cast<int_type>(1) - 2 < 0) {  // Signed
+    if (sizeof(i) > 32 / 8) {           // 33-bit to 64-bit
+      return numbers_internal::FastInt64ToBuffer(i, buffer);
+    } else {  // 32-bit or less
+      return numbers_internal::FastInt32ToBuffer(i, buffer);
+    }
+  } else {                     // Unsigned
+    if (sizeof(i) > 32 / 8) {  // 33-bit to 64-bit
+      return numbers_internal::FastUInt64ToBuffer(i, buffer);
+    } else {  // 32-bit or less
+      return numbers_internal::FastUInt32ToBuffer(i, buffer);
+    }
+  }
+}
+
+}  // namespace numbers_internal
+
+// SimpleAtoi()
+//
+// Converts a std::string to an integer, using `safe_strto?()` functions for actual
+// parsing, returning `true` if successful. The `safe_strto?()` functions apply
+// strict checking; the std::string must be a base-10 integer, optionally followed or
+// preceded by ASCII whitespace, with a value in the range of the corresponding
+// integer type.
+template <typename int_type>
+ABSL_MUST_USE_RESULT bool SimpleAtoi(absl::string_view s, int_type* out) {
+  static_assert(sizeof(*out) == 4 || sizeof(*out) == 8,
+                "SimpleAtoi works only with 32-bit or 64-bit integers.");
+  static_assert(!std::is_floating_point<int_type>::value,
+                "Use SimpleAtof or SimpleAtod instead.");
+  bool parsed;
+  // TODO(jorg): This signed-ness check is used because it works correctly
+  // with enums, and it also serves to check that int_type is not a pointer.
+  // If one day something like std::is_signed<enum E> works, switch to it.
+  if (static_cast<int_type>(1) - 2 < 0) {  // Signed
+    if (sizeof(*out) == 64 / 8) {       // 64-bit
+      int64_t val;
+      parsed = numbers_internal::safe_strto64_base(s, &val, 10);
+      *out = static_cast<int_type>(val);
+    } else {  // 32-bit
+      int32_t val;
+      parsed = numbers_internal::safe_strto32_base(s, &val, 10);
+      *out = static_cast<int_type>(val);
+    }
+  } else {                         // Unsigned
+    if (sizeof(*out) == 64 / 8) {  // 64-bit
+      uint64_t val;
+      parsed = numbers_internal::safe_strtou64_base(s, &val, 10);
+      *out = static_cast<int_type>(val);
+    } else {  // 32-bit
+      uint32_t val;
+      parsed = numbers_internal::safe_strtou32_base(s, &val, 10);
+      *out = static_cast<int_type>(val);
+    }
+  }
+  return parsed;
+}
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_NUMBERS_H_