clang-tools-extra/clang-tidy/bugprone/IncorrectRoundingsCheck.cpp

   1 //===--- IncorrectRoundingsCheck.cpp - clang-tidy ------------------------------===//
   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 "IncorrectRoundingsCheck.h"
  10 #include "clang/AST/DeclBase.h"
  11 #include "clang/AST/Type.h"
  12 #include "clang/ASTMatchers/ASTMatchFinder.h"
  13 #include "clang/ASTMatchers/ASTMatchers.h"
  14 #include "clang/Lex/Lexer.h"
  15
  16 using namespace clang::ast_matchers;
  17
  18 namespace clang::tidy::bugprone {
  19
  20 static llvm::APFloat getHalf(const llvm::fltSemantics &Semantics) {
  21   return llvm::APFloat(Semantics, 1U) / llvm::APFloat(Semantics, 2U);
  22 }
  23
  24 namespace {
  25 AST_MATCHER(FloatingLiteral, floatHalf) {
  26   return Node.getValue() == getHalf(Node.getSemantics());
  27 }
  28 } // namespace
  29
  30 void IncorrectRoundingsCheck::registerMatchers(MatchFinder *MatchFinder) {
  31   // Match a floating literal with value 0.5.
  32   auto FloatHalf = floatLiteral(floatHalf());
  33
  34   // Match a floating point expression.
  35   auto FloatType = expr(hasType(realFloatingPointType()));
  36
  37   // Find expressions of cast to int of the sum of a floating point expression
  38   // and 0.5.
  39   MatchFinder->addMatcher(
  40       traverse(TK_AsIs,
  41                implicitCastExpr(
  42                    hasImplicitDestinationType(isInteger()),
  43                    ignoringParenCasts(binaryOperator(
  44                        hasOperatorName("+"), hasOperands(FloatType, FloatType),
  45                        hasEitherOperand(ignoringParenImpCasts(FloatHalf)))))
  46                    .bind("CastExpr")),
  47       this);
  48 }
  49
  50 void IncorrectRoundingsCheck::check(const MatchFinder::MatchResult &Result) {
  51   const auto *CastExpr = Result.Nodes.getNodeAs<ImplicitCastExpr>("CastExpr");
  52   diag(CastExpr->getBeginLoc(),
  53        "casting (double + 0.5) to integer leads to incorrect rounding; "
  54        "consider using lround (#include <cmath>) instead");
  55 }
  56
  57 } // namespace clang::tidy::bugprone