[libcxx-commits] [libcxx] [libc++] Optimize ofstream::write (PR #123337)

[Louis Dionne via libcxx-commits]

================
@@ -0,0 +1,136 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+// UNSUPPORTED: c++03
+
+// <fstream>
+
+#include <algorithm>
+#include <cassert>
+#include <codecvt>
+#include <fstream>
+#include <locale>
+#include <vector>
+
+#include "platform_support.h"
+#include "test_macros.h"
+
+typedef std::filebuf::pos_type pos_type;
+typedef std::filebuf::off_type off_type;
+
+void sputn_seekoff(char* buf,
+                   const size_t buf_size,
+                   const std::streamsize chunk_size1,
+                   const off_type offset1,
+                   const std::streamsize chunk_size2) {
+  std::string data{"abcdefghijklmnopqrstuvwxyz"};
+  const std::streamsize data_size = static_cast<std::streamsize>(data.size());
+  assert(chunk_size1 <= data_size);
+  assert(chunk_size2 <= data_size);
+  // vector with expected data in the file to be written
+  std::size_t result_size = 5 + chunk_size1 + chunk_size2 + 1;
+  if (offset1 > 0) {
+    result_size += offset1;
+  }
+  std::vector<char> result(result_size, 0);
+  {
+    std::filebuf f;
+    f.pubsetbuf(buf, buf_size);
+    assert(f.open("sputn_seekoff.dat", std::ios_base::out) != 0);
+    assert(f.is_open());
+
+    assert(f.pubseekoff(off_type(5), std::ios_base::beg) = off_type(5));
+
+    std::vector<char> chunk(data.begin() + 5, data.begin() + 5 + chunk_size1);
+    std::copy(chunk.begin(), chunk.end(), result.begin() + 5);
+    const std::streamsize len1 = f.sputn(chunk.data(), chunk_size1);
+    assert(len1 == chunk_size1);
+    // check that nothing in the original chunk was modified by sputn()
+    assert(std::strncmp(chunk.data(), data.substr(5, len1).c_str(), len1) == 0);
+
+    pos_type p1 = f.pubseekoff(offset1, std::ios_base::cur);
+    char c;
+    if (p1 < 0) {
+      p1 = f.pubseekoff(0, std::ios_base::beg);
+      assert(p1 == 0);
+      c = '^';
+    } else {
+      assert(p1 == 5 + len1 + offset1);
+      if (p1 > data_size) {
+        c = '_';
+      } else {
+        c = data[p1];
+      }
+    }
+
+    result[p1] = c;
+    assert(f.sputc(c) == c);
+
+    f.pubseekpos(std::ios_base::beg);
+    result[0] = 'A';
+    assert(f.sputc(toupper(data[0])) == 'A');
+
+    pos_type end_pos = f.pubseekoff(off_type(0), std::ios_base::end);
+    assert(f.sputc(toupper(data[data_size - 1])) == 'Z');
+    result[end_pos] = 'Z';
+
+    assert(f.pubseekpos(p1) == p1);
+    result[p1] = toupper(c);
+    assert(f.sputc(toupper(c)) == toupper(c));
+
+    pos_type new_pos = result_size - chunk_size2;
+    pos_type p2      = f.pubseekoff(new_pos, std::ios_base::beg);
+    assert(p2 == new_pos);
+    chunk = std::vector<char>(data.end() - chunk_size2, data.end());
+    std::copy(chunk.begin(), chunk.end(), result.begin() + p2);
+    const std::streamsize len2 = f.sputn(chunk.data(), chunk_size2);
+    assert(len2 == chunk_size2);
+    assert(std::strncmp(chunk.data(), data.substr(data_size - chunk_size2, chunk_size2).c_str(), len2) == 0);
+    f.close();
+  }
+  std::filebuf f;
+  assert(f.open("sputn_seekoff.dat", std::ios_base::in) != 0);
+  assert(f.is_open());
+  std::vector<char> check(result.size(), -1);
+  const std::size_t len = f.sgetn(check.data(), check.size());
+  assert(len == result.size());
+  for (size_t i = 0; i < len; ++i) {
+    assert(check[i] == result[i]);
+  }
+}
+
+int main(int, char**) {
+  sputn_seekoff(nullptr, 10, 22, -27, 1);
+  sputn_seekoff(nullptr, 10, 1, -27, 1);
+  sputn_seekoff(nullptr, 10, 10, 14, 12);
+  sputn_seekoff(nullptr, 10, 1, -2, 1);
+  sputn_seekoff(nullptr, 10, 10, -4, 12);
+  sputn_seekoff(nullptr, 10, 11, -12, 3);
+  sputn_seekoff(nullptr, 10, 7, 3, 8);
+  sputn_seekoff(nullptr, 10, 5, -5, 12);
+  sputn_seekoff(nullptr, 10, 1, 1, 1);
+  sputn_seekoff(nullptr, 10, 9, 0, 1);
+
+  // // the below are very long duration tests to cover many possible variations of I/O and hit different corner cases
----------------
ldionne wrote:

Let's remove since this is actually incorrect.

https://github.com/llvm/llvm-project/pull/123337