[llvm] [clang] [clang-tools-extra] [clang-tidy] modernize-use-digit-separator issue #35414 (PR #76153)

[Piotr Zegar via cfe-commits]

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@@ -0,0 +1,235 @@
+//===--- UseDigitSeparatorCheck.cpp - clang-tidy --------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <algorithm>
+#include <iomanip>
+#include <numeric>
+#include <regex>
+#include <sstream>
+
+#include "UseDigitSeparatorCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+#include "llvm/Support/FormatVariadic.h"
+
+using namespace clang::ast_matchers;
+
+namespace {
+std::string
+getFormatedScientificFloatString(const llvm::StringRef OriginalLiteralString);
+
+std::vector<std::basic_string<char>>
+splitStringByGroupSize(const std::basic_string<char> &String,
+                       size_t GroupSize) {
+  std::vector<std::basic_string<char>> Result;
+  std::basic_string<char> ReversedString(String.rbegin(), String.rend());
+
+  for (size_t I = 0; I < ReversedString.size(); I += GroupSize) {
+    Result.push_back(ReversedString.substr(I, GroupSize));
+  }
+
+  std::reverse(Result.begin(), Result.end());
+  std::for_each(Result.begin(), Result.end(), [](std::basic_string<char> &Str) {
+    return std::reverse(Str.begin(), Str.end());
+  });
+
+  return Result;
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PiotrZSL wrote:

i do not like this algorithm, is not efficient. work something out without multiple copies,.

https://github.com/llvm/llvm-project/pull/76153