1 //===--- IncorrectRoundingsCheck.cpp - clang-tidy ------------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "IncorrectRoundingsCheck.h"
11 #include "clang/AST/DeclBase.h"
12 #include "clang/AST/Type.h"
13 #include "clang/ASTMatchers/ASTMatchFinder.h"
14 #include "clang/ASTMatchers/ASTMatchers.h"
15 #include "clang/Lex/Lexer.h"
16 
17 using namespace clang::ast_matchers;
18 
19 namespace clang {
20 namespace tidy {
21 namespace bugprone {
22 
23 namespace {
24 AST_MATCHER(FloatingLiteral, floatHalf) {
25   const auto &literal = Node.getValue();
26   if ((&Node.getSemantics()) == &llvm::APFloat::IEEEsingle())
27     return literal.convertToFloat() == 0.5f;
28   if ((&Node.getSemantics()) == &llvm::APFloat::IEEEdouble())
29     return literal.convertToDouble() == 0.5;
30   return false;
31 }
32 } // namespace
33 
34 void IncorrectRoundingsCheck::registerMatchers(MatchFinder *MatchFinder) {
35   // Match a floating literal with value 0.5.
36   auto FloatHalf = floatLiteral(floatHalf());
37 
38   // Match a floating point expression.
39   auto FloatType = expr(hasType(realFloatingPointType()));
40 
41   // Match a floating literal of 0.5 or a floating literal of 0.5 implicitly.
42   // cast to floating type.
43   auto FloatOrCastHalf =
44       anyOf(FloatHalf,
45             implicitCastExpr(FloatType, has(ignoringParenImpCasts(FloatHalf))));
46 
47   // Match if either the LHS or RHS is a floating literal of 0.5 or a floating
48   // literal of 0.5 and the other is of type double or vice versa.
49   auto OneSideHalf = anyOf(allOf(hasLHS(FloatOrCastHalf), hasRHS(FloatType)),
50                            allOf(hasRHS(FloatOrCastHalf), hasLHS(FloatType)));
51 
52   // Find expressions of cast to int of the sum of a floating point expression
53   // and 0.5.
54   MatchFinder->addMatcher(
55       implicitCastExpr(
56           hasImplicitDestinationType(isInteger()),
57           ignoringParenCasts(binaryOperator(hasOperatorName("+"), OneSideHalf)))
58           .bind("CastExpr"),
59       this);
60 }
61 
62 void IncorrectRoundingsCheck::check(const MatchFinder::MatchResult &Result) {
63   const auto *CastExpr = Result.Nodes.getNodeAs<ImplicitCastExpr>("CastExpr");
64   diag(CastExpr->getLocStart(),
65        "casting (double + 0.5) to integer leads to incorrect rounding; "
66        "consider using lround (#include <cmath>) instead");
67 }
68 
69 } // namespace bugprone
70 } // namespace tidy
71 } // namespace clang
72