1 files changed, 74 insertions, 0 deletions
diff --git a/clang-tools-extra/clang-tidy/misc/IncorrectRoundings.cpp b/clang-tools-extra/clang-tidy/misc/IncorrectRoundings.cpp
new file mode 100644
index 00000000000..993af51d53e
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/misc/IncorrectRoundings.cpp
@@ -0,0 +1,74 @@
+//===--- IncorrectRoundings.cpp - clang-tidy ------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "IncorrectRoundings.h"
+#include "clang/AST/DeclBase.h"
+#include "clang/AST/Type.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Lex/Lexer.h"
+
+namespace clang {
+namespace ast_matchers {
+AST_MATCHER(FloatingLiteral, floatHalf) {
+  const auto &literal = Node.getValue();
+  if ((&Node.getSemantics()) == &llvm::APFloat::IEEEsingle)
+    return literal.convertToFloat() == 0.5f;
+  if ((&Node.getSemantics()) == &llvm::APFloat::IEEEdouble)
+    return literal.convertToDouble() == 0.5;
+  return false;
+}
+
+// TODO(hokein): Moving it to ASTMatchers.h
+AST_MATCHER(BuiltinType, isFloatingPoint) {
+  return Node.isFloatingPoint();
+}
+} // namespace ast_matchers
+} // namespace clang
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+void IncorrectRoundings::registerMatchers(MatchFinder *MatchFinder) {
+  // Match a floating literal with value 0.5.
+  auto FloatHalf = floatLiteral(floatHalf());
+
+  // Match a floating point expression.
+  auto FloatType = expr(hasType(builtinType(isFloatingPoint())));
+
+  // Match a floating literal of 0.5 or a floating literal of 0.5 implicitly.
+  // cast to floating type.
+  auto FloatOrCastHalf =
+      anyOf(FloatHalf, implicitCastExpr(FloatType, has(FloatHalf)));
+
+  // Match if either the LHS or RHS is a floating literal of 0.5 or a floating
+  // literal of 0.5 and the other is of type double or vice versa.
+  auto OneSideHalf = anyOf(allOf(hasLHS(FloatOrCastHalf), hasRHS(FloatType)),
+                           allOf(hasRHS(FloatOrCastHalf), hasLHS(FloatType)));
+
+  // Find expressions of cast to int of the sum of a floating point expression
+  // and 0.5.
+  MatchFinder->addMatcher(
+      implicitCastExpr(
+          hasImplicitDestinationType(isInteger()),
+          ignoringParenCasts(binaryOperator(hasOperatorName("+"), OneSideHalf)))
+          .bind("CastExpr"),
+      this);
+}
+
+void IncorrectRoundings::check(const MatchFinder::MatchResult &Result) {
+  const auto *CastExpr = Result.Nodes.getStmtAs<ImplicitCastExpr>("CastExpr");
+  diag(CastExpr->getLocStart(),
+       "casting (double + 0.5) to integer leads to incorrect rounding; "
+       "consider using lround (#include <cmath>) instead");
+}
+
+} // namespace tidy
+} // namespace clang