[libcxx] [test] Add a test for the range of file offsets (#122798)

This adds a test for an issue reported downstream at
mstorsjo/llvm-mingw#462; this is known to fail
on Windows right now, where the fseek/ftell calls end up truncated to 32
bits.

The test for this, unfortunately, requires temporarily creating a 4 GB
file.

Author: mstorsjo

libcxx/test/std/input.output/file.streams/fstreams/ifstream.members/offset_range.pass.cpp

@@ -0,0 +1,82 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <fstream>
+
+// Test that we can seek using offsets larger than 32 bit, and that we can
+// retrieve file offsets larger than 32 bit.
+
+// On MSVC targets, we only use the 32 bit fseek/ftell functions. For MinGW
+// targets, we use fseeko/ftello, but the user needs to define
+// _FILE_OFFSET_BITS=64 to make them 64 bit.
+//
+// XFAIL: target={{.*}}-windows{{.*}}
+
+// On 32 bit Android platforms, off_t is 32 bit by default. By defining
+// _FILE_OFFSET_BITS=64, one gets a 64 bit off_t, but the corresponding
+// 64 bit ftello/fseeko functions are only available since Android API 24 (7.0).
+// (On 64 bit Android platforms, off_t has always been 64 bit.)
+//
+// XFAIL: target={{i686|arm.*}}-{{.+}}-android{{.*}}
+
+// Writing the >4 GB test file fails on 32 bit AIX.
+//
+// XFAIL: target=powerpc-{{.+}}-aix{{.*}}
+
+#include <fstream>
+#include <iostream>
+#include <cassert>
+#include <vector>
+
+#include "assert_macros.h"
+#include "platform_support.h"
+#include "test_macros.h"
+
+void test_tellg(std::streamoff total_size) {
+  std::vector<char> data(8192);
+  for (std::size_t i = 0; i < data.size(); ++i)
+    data[i] = static_cast<char>(i % (1 << 8 * sizeof(char)));
+  std::string p = get_temp_file_name();
+  {
+    std::ofstream ofs;
+    ofs.open(p, std::ios::out | std::ios::binary);
+    assert(ofs.is_open());
+    for (std::streamoff size = 0; size < total_size;) {
+      std::size_t n = std::min(static_cast<std::streamoff>(data.size()), total_size - size);
+      ofs.write(data.data(), n);
+      size += n;
+    }
+    assert(!ofs.fail());
+    ofs.close();
+  }
+  {
+    std::ifstream ifs;
+    ifs.open(p, std::ios::binary);
+    assert(ifs.is_open());
+    std::streamoff in_off = ifs.tellg();
+    TEST_REQUIRE(in_off == 0, "in_off not zero at start");
+    ifs.seekg(total_size - 20, std::ios::beg);
+    in_off = ifs.tellg();
+    TEST_REQUIRE(in_off == total_size - 20, "in_off incorrect after >32 bit seek");
+    ifs.seekg(10, std::ios::cur);
+    in_off = ifs.tellg();
+    TEST_REQUIRE(in_off == total_size - 10, "in_off incorrect after incremental seek");
+    ifs.seekg(0, std::ios::end);
+    in_off = ifs.tellg();
+    TEST_REQUIRE(in_off == total_size, "in_off incorrect after seek to end");
+  }
+  std::remove(p.c_str());
+}
+
+int main(int, char**) {
+  // This test assumes and requires that std::streamoff is larger than
+  // 32 bit - this is not required in the standard itself.
+  static_assert(sizeof(std::streamoff) > 4, "");
+  test_tellg(0x100000042ULL);
+  return 0;
+}