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diff --git a/absl/strings/internal/pow10_helper.h b/absl/strings/internal/pow10_helper.h
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+//
+// Copyright 2018 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.
+//
+// This test helper library contains a table of powers of 10, to guarantee
+// precise values are computed across the full range of doubles. We can't rely
+// on the pow() function, because not all standard libraries ship a version
+// that is precise.
+#ifndef ABSL_STRINGS_POW10_HELPER_H_
+#define ABSL_STRINGS_POW10_HELPER_H_
+
+#include <vector>
+
+namespace absl {
+namespace strings_internal {
+
+// Computes the precise value of 10^exp. (I.e. the nearest representable
+// double to the exact value, rounding to nearest-even in the (single) case of
+// being exactly halfway between.)
+double Pow10(int exp);
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_POW10_HELPER_H_