116 lines
3.8 KiB
C++
116 lines
3.8 KiB
C++
// Copyright 2020 The Pigweed Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not
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// use this file except in compliance with the License. You may obtain a copy of
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// the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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// License for the specific language governing permissions and limitations under
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// the License.
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//
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// This tests the system installed C standard library version of memset.
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//
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// Note: We have caught real production bugs with these tests. Do not assume
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// your vendor's C library is correct! For standard C functions like memset and
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// memcpy, there are compiler intrisics which assume that the C standard is
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// followed. If the implemention of memset or memcpy does not exactly follow
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// the standard, subtle and hard to track down bugs can be the result.
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#include <array>
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#include <cstring>
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#include <numeric>
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#include "gtest/gtest.h"
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namespace pw {
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namespace {
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// From the ISO C standard:
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// http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf
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//
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// Section 7.21.6.1: memset(void *s, int c, size_t n)
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//
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// void* memset(void* buffer,
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// int character,
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// size_t num_bytes);
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//
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// Copy c into the first n bytes of s.
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// Returns buffer, a copy of the destination pointer.
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//
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TEST(Memset, EmptyCase) {
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std::array<char, 5> arr{'h', 'e', 'l', 'l', 'o'};
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void* ret = memset(arr.data(), 0, 0);
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// Destination buffer returned.
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EXPECT_EQ(ret, arr.data());
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// Destination buffer untouched.
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constexpr std::array<char, 5> kExpected{'h', 'e', 'l', 'l', 'o'};
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EXPECT_TRUE(
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std::equal(arr.begin(), arr.end(), kExpected.begin(), kExpected.end()));
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}
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TEST(Memset, OneCharacter) {
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std::array<char, 5> arr{'h', 'e', 'l', 'l', 'o'};
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void* ret = memset(arr.data(), 0, 1);
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// Ensure the destination buffer is returned.
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EXPECT_EQ(ret, arr.data());
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// Ensure the destination buffer is untouched.
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constexpr std::array<char, 5> kExpected{0, 'e', 'l', 'l', 'o'};
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EXPECT_TRUE(
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std::equal(arr.begin(), arr.end(), kExpected.begin(), kExpected.end()));
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}
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// Now do a detailed case with more values. Span both word sizes and alignments
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// to ensure we hit some edge cases.
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TEST(Memset, MultipleSizesMultipleAlignments) {
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constexpr int kMaxBytes = 64;
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std::array<char, kMaxBytes> arr;
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constexpr int kMaxAlignment = 16;
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// Avoid 0 sentinel to prevent interaction with uninitialized memory.
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constexpr char kSentinel = 3;
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constexpr char kIotaStart = kSentinel + 7;
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// Try different alignments.
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for (int alignment = 0; alignment < kMaxAlignment; ++alignment) {
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// Try different memset sizes.
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for (int write_size = 0; write_size < (kMaxBytes - kMaxAlignment);
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++write_size) {
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// Fill entire array with incrementing integers; starting above sentinel.
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std::iota(arr.begin(), arr.end(), kIotaStart);
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// Memset the first write_size bytes, with our sentinel
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void* write_head = &arr[alignment];
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const void* ret = memset(write_head, kSentinel, write_size);
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// Check destination buffer returned.
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EXPECT_EQ(ret, write_head);
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for (int j = 0; j < kMaxBytes; ++j) {
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if (j < alignment) {
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// First part of destination buffer untouched; should match iota.
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EXPECT_EQ(arr[j], kIotaStart + j);
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} else if (j < alignment + write_size) {
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// Second part is set to the sentinel value.
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EXPECT_EQ(arr[j], kSentinel);
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} else {
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// Third part is back to the iota content.
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EXPECT_EQ(arr[j], kIotaStart + j);
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}
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}
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}
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}
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}
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} // namespace
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} // namespace pw
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