SERVER-21404 Introduce some useful 64-bit arithmetic with overflow detection functions.

3 files changed, 249 insertions, 0 deletions

diff --git a/src/mongo/platform/SConscript b/src/mongo/platform/SConscript
index 6f74069ce3d..518cc620f3f 100644
--- a/src/mongo/platform/SConscript
+++ b/src/mongo/platform/SConscript
@@ -28,3 +28,4 @@ env.CppUnitTest('process_id_test', 'process_id_test.cpp', LIBDEPS=['platform'])
 env.CppUnitTest('random_test', 'random_test.cpp', LIBDEPS=['$BUILD_DIR/mongo/base'])
 env.CppUnitTest('stack_locator_test', 'stack_locator_test.cpp', LIBDEPS=['platform'])
 env.CppUnitTest('decimal128_test', 'decimal128_test.cpp', LIBDEPS=['$BUILD_DIR/mongo/base'])
+env.CppUnitTest('overflow_arithmetic_test', 'overflow_arithmetic_test.cpp')
diff --git a/src/mongo/platform/overflow_arithmetic.h b/src/mongo/platform/overflow_arithmetic.h
new file mode 100644
index 00000000000..8dc3940d0f4
--- /dev/null
+++ b/src/mongo/platform/overflow_arithmetic.h
@@ -0,0 +1,126 @@
+/*    Copyright 2016 MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+
+#pragma once
+
+#include <cstdint>
+
+#ifdef _MSC_VER
+#include <intrin.h>
+#endif
+
+namespace mongo {
+
+/**
+ * Returns true if multiplying lhs by rhs would overflow. Otherwise, ultiplies 64-bit signed
+ * integers lhs by rhs and stores the result in *product.
+ */
+inline bool mongoSignedMultiplyOverflow64(int64_t lhs, int64_t rhs, int64_t* product);
+
+/**
+ * Returns true if adding lhs and rhs would overflow. Otherwise, adds 64-bit signed integers lhs and
+ * rhs and stores the result in *sum.
+ */
+inline bool mongoSignedAddOverflow64(int64_t lhs, int64_t rhs, int64_t* sum);
+
+/**
+ * Returns true if subtracting rhs from lhs would overflow. Otherwise, subtracts 64-bit signed
+ * integers rhs from lhs and stores the result in *difference.
+ */
+inline bool mongoSignedSubtractOverflow64(int64_t lhs, int64_t rhs, int64_t* difference);
+
+
+#ifdef _MSC_VER
+
+// In MSVC, we use an MSVC intrinsic for the multiplication form of this calculation, and unsigned
+// arithmetic and careful casting for addition and subtraction.
+
+inline bool mongoSignedMultiplyOverflow64(int64_t lhs, int64_t rhs, int64_t* product) {
+    int64_t hi;
+    *product = _mul128(lhs, rhs, &hi);
+    if (hi == 0) {
+        return *product < 0;
+    }
+    if (hi == -1) {
+        return *product >= 0;
+    }
+    return true;
+}
+
+inline bool mongoSignedAddOverflow64(int64_t lhs, int64_t rhs, int64_t* sum) {
+    *sum = static_cast<int64_t>(static_cast<uint64_t>(lhs) + static_cast<uint64_t>(rhs));
+    if (lhs >= 0 && rhs >= 0) {
+        return (*sum) < 0;
+    }
+    if (lhs < 0 && rhs < 0) {
+        return (*sum) >= 0;
+    }
+    return false;
+}
+
+inline bool mongoSignedSubtractOverflow64(int64_t lhs, int64_t rhs, int64_t* difference) {
+    *difference = static_cast<int64_t>(static_cast<uint64_t>(lhs) - static_cast<uint64_t>(rhs));
+    if (lhs >= 0 && rhs < 0) {
+        return (*difference) < 0;
+    }
+    if (lhs < 0 && rhs >= 0) {
+        return (*difference >= 0);
+    }
+    return false;
+}
+
+#else
+
+// On GCC and CLANG we can use __builtin functions to perform these calculations.
+
+inline bool mongoSignedMultiplyOverflow64(long lhs, long rhs, long* product) {
+    return __builtin_smull_overflow(lhs, rhs, product);
+}
+
+inline bool mongoSignedAddOverflow64(long lhs, long rhs, long* sum) {
+    return __builtin_saddl_overflow(lhs, rhs, sum);
+}
+
+inline bool mongoSignedSubtractOverflow64(long lhs, long rhs, long* difference) {
+    return __builtin_ssubl_overflow(lhs, rhs, difference);
+}
+
+inline bool mongoSignedMultiplyOverflow64(long long lhs, long long rhs, long long* product) {
+    return __builtin_smulll_overflow(lhs, rhs, product);
+}
+
+inline bool mongoSignedAddOverflow64(long long lhs, long long rhs, long long* sum) {
+    return __builtin_saddll_overflow(lhs, rhs, sum);
+}
+
+inline bool mongoSignedSubtractOverflow64(long long lhs, long long rhs, long long* difference) {
+    return __builtin_ssubll_overflow(lhs, rhs, difference);
+}
+
+#endif
+
+}  // namespace mongo
diff --git a/src/mongo/platform/overflow_arithmetic_test.cpp b/src/mongo/platform/overflow_arithmetic_test.cpp
new file mode 100644
index 00000000000..5a1851fbf81
--- /dev/null
+++ b/src/mongo/platform/overflow_arithmetic_test.cpp
@@ -0,0 +1,122 @@
+/*    Copyright 2016 MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include <limits>
+
+#include "mongo/platform/overflow_arithmetic.h"
+#include "mongo/unittest/unittest.h"
+
+namespace mongo {
+namespace {
+
+using limits = std::numeric_limits<int64_t>;
+
+#define assertArithOverflow(FN, LHS, RHS, EXPECT_OVERFLOW, EXPECTED_RESULT)         \
+    do {                                                                            \
+        const bool expectOverflow = EXPECT_OVERFLOW;                                \
+        int64_t result;                                                             \
+        ASSERT_EQ(expectOverflow, FN(LHS, RHS, &result)) << #FN "(" #LHS ", " #RHS; \
+        if (!expectOverflow) {                                                      \
+            ASSERT_EQ(EXPECTED_RESULT, result) << #FN "(" #LHS ", " #RHS " - >";    \
+        }                                                                           \
+    } while (false)
+
+#define assertMultiplyNoOverflow(LHS, RHS, EXPECTED) \
+    assertArithOverflow(mongoSignedMultiplyOverflow64, LHS, RHS, false, EXPECTED)
+#define assertMultiplyWithOverflow(LHS, RHS) \
+    assertArithOverflow(mongoSignedMultiplyOverflow64, LHS, RHS, true, 0)
+
+#define assertAddNoOverflow(LHS, RHS, EXPECTED) \
+    assertArithOverflow(mongoSignedAddOverflow64, LHS, RHS, false, EXPECTED)
+#define assertAddWithOverflow(LHS, RHS) \
+    assertArithOverflow(mongoSignedAddOverflow64, LHS, RHS, true, 0)
+
+#define assertSubtractNoOverflow(LHS, RHS, EXPECTED) \
+    assertArithOverflow(mongoSignedSubtractOverflow64, LHS, RHS, false, EXPECTED)
+#define assertSubtractWithOverflow(LHS, RHS) \
+    assertArithOverflow(mongoSignedSubtractOverflow64, LHS, RHS, true, 0)
+
+TEST(OverflowArithmetic, MultiplicationTests) {
+    assertMultiplyNoOverflow(0, limits::max(), 0);
+    assertMultiplyNoOverflow(0, limits::min(), 0);
+    assertMultiplyNoOverflow(1, limits::max(), limits::max());
+    assertMultiplyNoOverflow(1, limits::min(), limits::min());
+    assertMultiplyNoOverflow(-1, limits::max(), limits::min() + 1);
+    assertMultiplyNoOverflow(1000, 57, 57000);
+    assertMultiplyNoOverflow(1000, -57, -57000);
+    assertMultiplyNoOverflow(-1000, -57, 57000);
+    assertMultiplyNoOverflow(0x3fffffffffffffff, 2, 0x7ffffffffffffffe);
+    assertMultiplyNoOverflow(0x3fffffffffffffff, -2, -0x7ffffffffffffffe);
+    assertMultiplyNoOverflow(-0x3fffffffffffffff, -2, 0x7ffffffffffffffe);
+
+    assertMultiplyWithOverflow(-1, limits::min());
+    assertMultiplyWithOverflow(2, limits::max());
+    assertMultiplyWithOverflow(-2, limits::max());
+    assertMultiplyWithOverflow(2, limits::min());
+    assertMultiplyWithOverflow(-2, limits::min());
+    assertMultiplyWithOverflow(limits::min(), limits::max());
+    assertMultiplyWithOverflow(limits::max(), limits::max());
+    assertMultiplyWithOverflow(limits::min(), limits::min());
+    assertMultiplyWithOverflow(1LL << 62, 8);
+    assertMultiplyWithOverflow(-(1LL << 62), 8);
+    assertMultiplyWithOverflow(-(1LL << 62), -8);
+}
+
+TEST(OverflowArithmetic, AdditionTests) {
+    assertAddNoOverflow(0, limits::max(), limits::max());
+    assertAddNoOverflow(-1, limits::max(), limits::max() - 1);
+    assertAddNoOverflow(0, limits::min(), limits::min());
+    assertAddNoOverflow(1, limits::min(), limits::min() + 1);
+    assertAddNoOverflow(limits::max(), limits::min(), -1);
+    assertAddNoOverflow(1, 1, 2);
+    assertAddNoOverflow(-1, -1, -2);
+
+    assertAddWithOverflow(limits::max(), 1);
+    assertAddWithOverflow(limits::max(), limits::max());
+    assertAddWithOverflow(limits::min(), -1);
+    assertAddWithOverflow(limits::min(), limits::min());
+}
+
+TEST(OverflowArithmetic, SubtractionTests) {
+    assertSubtractNoOverflow(limits::max(), 0, limits::max());
+    assertSubtractNoOverflow(limits::max(), 1, limits::max() - 1);
+    assertSubtractNoOverflow(limits::min(), 0, limits::min());
+    assertSubtractNoOverflow(limits::min(), -1, limits::min() + 1);
+    assertSubtractNoOverflow(limits::max(), limits::max(), 0);
+    assertSubtractNoOverflow(limits::min(), limits::min(), 0);
+
+    assertSubtractWithOverflow(0, limits::min());
+    assertSubtractWithOverflow(limits::max(), -1);
+    assertSubtractWithOverflow(limits::max(), limits::min());
+    assertSubtractWithOverflow(limits::min(), 1);
+    assertSubtractWithOverflow(limits::min(), limits::max());
+}
+
+}  // namespace
+}  // namespace mongo