1 //===-- runtime/buffer.cpp --------------------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "buffer.h"
10 #include <algorithm>
11 
12 namespace Fortran::runtime::io {
13 
14 // Here's a very old trick for shifting circular buffer data cheaply
15 // without a need for a temporary array.
LeftShiftBufferCircularly(char * buffer,std::size_t bytes,std::size_t shift)16 void LeftShiftBufferCircularly(
17     char *buffer, std::size_t bytes, std::size_t shift) {
18   // Assume that we start with "efgabcd" and the left shift is 3.
19   std::reverse(buffer, buffer + shift); // "gfeabcd"
20   std::reverse(buffer, buffer + bytes); // "dcbaefg"
21   std::reverse(buffer, buffer + bytes - shift); // "abcdefg"
22 }
23 } // namespace Fortran::runtime::io
24