[llvm] r326516 - Utility functions for checked arithmetic
George Karpenkov via llvm-commits
llvm-commits at lists.llvm.org
Fri Mar 2 10:19:18 PST 2018
Yes, but I thought that it would be even worse.
I also wanted to cater for the case where the user just wants to check for the overflow without caring about the result.
> On Mar 2, 2018, at 9:17 AM, Philip Reames <listmail at philipreames.com> wrote:
>
> Using out params is a bit ugly for this. Did you consider either returning pair, struct, or optional result?
>
> Philip
>
>
> On 03/01/2018 04:30 PM, George Karpenkov via llvm-commits wrote:
>> Author: george.karpenkov
>> Date: Thu Mar 1 16:30:43 2018
>> New Revision: 326516
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=326516&view=rev
>> Log:
>> Utility functions for checked arithmetic
>>
>> Provide checkedAdd and checkedMul functions, providing checked
>> arithmetic on signed integers.
>>
>> Differential Revision: https://reviews.llvm.org/D43704
>>
>> Added:
>> llvm/trunk/include/llvm/Support/CheckedArithmetic.h
>> llvm/trunk/unittests/Support/CheckedArithmeticTest.cpp
>> Modified:
>> llvm/trunk/unittests/Support/CMakeLists.txt
>>
>> Added: llvm/trunk/include/llvm/Support/CheckedArithmetic.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/CheckedArithmetic.h?rev=326516&view=auto
>> ==============================================================================
>> --- llvm/trunk/include/llvm/Support/CheckedArithmetic.h (added)
>> +++ llvm/trunk/include/llvm/Support/CheckedArithmetic.h Thu Mar 1 16:30:43 2018
>> @@ -0,0 +1,83 @@
>> +//==-- llvm/Support/CheckedArithmetic.h - Safe arithmetical operations *- C++ //
>> +//
>> +// The LLVM Compiler Infrastructure
>> +//
>> +// This file is distributed under the University of Illinois Open Source
>> +// License. See LICENSE.TXT for details.
>> +//
>> +//===----------------------------------------------------------------------===//
>> +//
>> +// This file contains generic functions for operating on integers which
>> +// give the indication on whether the operation has overflown.
>> +//
>> +//===----------------------------------------------------------------------===//
>> +
>> +#ifndef LLVM_SUPPORT_CHECKEDARITHMETIC_H
>> +#define LLVM_SUPPORT_CHECKEDARITHMETIC_H
>> +
>> +#include "llvm/ADT/APInt.h"
>> +
>> +#include <type_traits>
>> +
>> +namespace {
>> +
>> +/// Utility function to apply a given method of \c APInt \p F to \p LHS and
>> +/// \p RHS, and write the output into \p Res.
>> +/// \return Whether the operation overflows.
>> +template <typename T, typename F>
>> +typename std::enable_if<std::is_integral<T>::value && sizeof(T) * 8 <= 64,
>> + bool>::type
>> +checkedOp(T LHS, T RHS, F Op, T *Res = nullptr, bool Signed = true) {
>> + llvm::APInt ALHS(/*BitSize=*/sizeof(T) * 8, LHS, Signed);
>> + llvm::APInt ARHS(/*BitSize=*/sizeof(T) * 8, RHS, Signed);
>> + bool Overflow;
>> + llvm::APInt Out = (ALHS.*Op)(ARHS, Overflow);
>> + if (Res)
>> + *Res = Signed ? Out.getSExtValue() : Out.getZExtValue();
>> + return Overflow;
>> +}
>> +}
>> +
>> +namespace llvm {
>> +
>> +/// Add two signed integers \p LHS and \p RHS, write into \p Res if non-null.
>> +/// Does not guarantee saturating arithmetic.
>> +/// \return Whether the result overflows.
>> +template <typename T>
>> +typename std::enable_if<std::is_signed<T>::value, bool>::type
>> +checkedAdd(T LHS, T RHS, T *Res = nullptr) {
>> + return checkedOp(LHS, RHS, &llvm::APInt::sadd_ov, Res);
>> +}
>> +
>> +/// Multiply two signed integers \p LHS and \p RHS, write into \p Res if
>> +/// non-null.
>> +/// Does not guarantee saturating arithmetic.
>> +/// \return Whether the result overflows.
>> +template <typename T>
>> +typename std::enable_if<std::is_signed<T>::value, bool>::type
>> +checkedMul(T LHS, T RHS, T *Res = nullptr) {
>> + return checkedOp(LHS, RHS, &llvm::APInt::smul_ov, Res);
>> +}
>> +
>> +/// Add two unsigned integers \p LHS and \p RHS, write into \p Res if non-null.
>> +/// Does not guarantee saturating arithmetic.
>> +/// \return Whether the result overflows.
>> +template <typename T>
>> +typename std::enable_if<std::is_unsigned<T>::value, bool>::type
>> +checkedAddUnsigned(T LHS, T RHS, T *Res = nullptr) {
>> + return checkedOp(LHS, RHS, &llvm::APInt::uadd_ov, Res, /*Signed=*/false);
>> +}
>> +
>> +/// Multiply two unsigned integers \p LHS and \p RHS, write into \p Res if
>> +/// non-null.
>> +/// Does not guarantee saturating arithmetic.
>> +/// \return Whether the result overflows.
>> +template <typename T>
>> +typename std::enable_if<std::is_unsigned<T>::value, bool>::type
>> +checkedMulUnsigned(T LHS, T RHS, T *Res = nullptr) {
>> + return checkedOp(LHS, RHS, &llvm::APInt::umul_ov, Res, /*Signed=*/false);
>> +}
>> +
>> +} // End llvm namespace
>> +
>> +#endif
>>
>> Modified: llvm/trunk/unittests/Support/CMakeLists.txt
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Support/CMakeLists.txt?rev=326516&r1=326515&r2=326516&view=diff
>> ==============================================================================
>> --- llvm/trunk/unittests/Support/CMakeLists.txt (original)
>> +++ llvm/trunk/unittests/Support/CMakeLists.txt Thu Mar 1 16:30:43 2018
>> @@ -13,6 +13,7 @@ add_llvm_unittest(SupportTests
>> CachePruningTest.cpp
>> CrashRecoveryTest.cpp
>> Casting.cpp
>> + CheckedArithmeticTest.cpp
>> Chrono.cpp
>> CommandLineTest.cpp
>> CompressionTest.cpp
>>
>> Added: llvm/trunk/unittests/Support/CheckedArithmeticTest.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Support/CheckedArithmeticTest.cpp?rev=326516&view=auto
>> ==============================================================================
>> --- llvm/trunk/unittests/Support/CheckedArithmeticTest.cpp (added)
>> +++ llvm/trunk/unittests/Support/CheckedArithmeticTest.cpp Thu Mar 1 16:30:43 2018
>> @@ -0,0 +1,71 @@
>> +#include "llvm/Support/CheckedArithmetic.h"
>> +#include "gtest/gtest.h"
>> +
>> +using namespace llvm;
>> +
>> +namespace {
>> +
>> +TEST(CheckedArithmetic, CheckedAdd) {
>> + int64_t Out;
>> + const int64_t Max = std::numeric_limits<int64_t>::max();
>> + const int64_t Min = std::numeric_limits<int64_t>::min();
>> + EXPECT_EQ(checkedAdd<int64_t>(Max, Max, &Out), true);
>> + EXPECT_EQ(checkedAdd<int64_t>(Min, -1, &Out), true);
>> + EXPECT_EQ(checkedAdd<int64_t>(Max, 1, &Out), true);
>> + EXPECT_EQ(checkedAdd<int64_t>(10, 1, &Out), false);
>> + EXPECT_EQ(Out, 11);
>> +}
>> +
>> +TEST(CheckedArithmetic, CheckedAddSmall) {
>> + int16_t Out;
>> + const int16_t Max = std::numeric_limits<int16_t>::max();
>> + const int16_t Min = std::numeric_limits<int16_t>::min();
>> + EXPECT_EQ(checkedAdd<int16_t>(Max, Max, &Out), true);
>> + EXPECT_EQ(checkedAdd<int16_t>(Min, -1, &Out), true);
>> + EXPECT_EQ(checkedAdd<int16_t>(Max, 1, &Out), true);
>> + EXPECT_EQ(checkedAdd<int16_t>(10, 1, &Out), false);
>> + EXPECT_EQ(Out, 11);
>> +}
>> +
>> +TEST(CheckedArithmetic, CheckedMul) {
>> + int64_t Out;
>> + const int64_t Max = std::numeric_limits<int64_t>::max();
>> + const int64_t Min = std::numeric_limits<int64_t>::min();
>> + EXPECT_EQ(checkedMul<int64_t>(Max, 2, &Out), true);
>> + EXPECT_EQ(checkedMul<int64_t>(Max, Max, &Out), true);
>> + EXPECT_EQ(checkedMul<int64_t>(Min, 2, &Out), true);
>> + EXPECT_EQ(checkedMul<int64_t>(10, 2, &Out), false);
>> + EXPECT_EQ(Out, 20);
>> +}
>> +
>> +TEST(CheckedArithmetic, CheckedMulSmall) {
>> + int16_t Out;
>> + const int16_t Max = std::numeric_limits<int16_t>::max();
>> + const int16_t Min = std::numeric_limits<int16_t>::min();
>> + EXPECT_EQ(checkedMul<int16_t>(Max, 2, &Out), true);
>> + EXPECT_EQ(checkedMul<int16_t>(Max, Max, &Out), true);
>> + EXPECT_EQ(checkedMul<int16_t>(Min, 2, &Out), true);
>> + EXPECT_EQ(checkedMul<int16_t>(10, 2, &Out), false);
>> + EXPECT_EQ(Out, 20);
>> +}
>> +
>> +TEST(CheckedArithmetic, CheckedAddUnsigned) {
>> + uint64_t Out;
>> + const uint64_t Max = std::numeric_limits<uint64_t>::max();
>> + EXPECT_EQ(checkedAddUnsigned<uint64_t>(Max, Max, &Out), true);
>> + EXPECT_EQ(checkedAddUnsigned<uint64_t>(Max, 1, &Out), true);
>> + EXPECT_EQ(checkedAddUnsigned<uint64_t>(10, 1, &Out), false);
>> + EXPECT_EQ(Out, uint64_t(11));
>> +}
>> +
>> +TEST(CheckedArithmetic, CheckedMulUnsigned) {
>> + uint64_t Out;
>> + const uint64_t Max = std::numeric_limits<uint64_t>::max();
>> + EXPECT_EQ(checkedMulUnsigned<uint64_t>(Max, 2, &Out), true);
>> + EXPECT_EQ(checkedMulUnsigned<uint64_t>(Max, Max, &Out), true);
>> + EXPECT_EQ(checkedMulUnsigned<uint64_t>(10, 2, &Out), false);
>> + EXPECT_EQ(Out, uint64_t(20));
>> +}
>> +
>> +
>> +} // namespace
>>
>>
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