1 files changed, 94 insertions, 0 deletions
diff --git a/klm/util/fake_ofstream.hh b/klm/util/fake_ofstream.hh
new file mode 100644
index 00000000..bcdebe45
--- /dev/null
+++ b/klm/util/fake_ofstream.hh
@@ -0,0 +1,94 @@
+/* Like std::ofstream but without being incredibly slow.  Backed by a raw fd.
+ * Does not support many data types.  Currently, it's targeted at writing ARPA
+ * files quickly.
+ */
+#include "util/double-conversion/double-conversion.h"
+#include "util/double-conversion/utils.h"
+#include "util/file.hh"
+#include "util/scoped.hh"
+#include "util/string_piece.hh"
+
+#define BOOST_LEXICAL_CAST_ASSUME_C_LOCALE
+#include <boost/lexical_cast.hpp>
+
+namespace util {
+class FakeOFStream {
+  public:
+    static const std::size_t kOutBuf = 1048576;
+
+    // Does not take ownership of out.
+    explicit FakeOFStream(int out)
+      : buf_(util::MallocOrThrow(kOutBuf)),
+        builder_(static_cast<char*>(buf_.get()), kOutBuf),
+        // Mostly the default but with inf instead.  And no flags.
+        convert_(double_conversion::DoubleToStringConverter::NO_FLAGS, "inf", "NaN", 'e', -6, 21, 6, 0),
+        fd_(out) {}
+
+    ~FakeOFStream() {
+      if (buf_.get()) Flush();
+    }
+
+    FakeOFStream &operator<<(float value) {
+      // Odd, but this is the largest number found in the comments.
+      EnsureRemaining(double_conversion::DoubleToStringConverter::kMaxPrecisionDigits + 8);
+      convert_.ToShortestSingle(value, &builder_);
+      return *this;
+    }
+
+    FakeOFStream &operator<<(double value) {
+      EnsureRemaining(double_conversion::DoubleToStringConverter::kMaxPrecisionDigits + 8);
+      convert_.ToShortest(value, &builder_);
+      return *this;
+    }
+
+    FakeOFStream &operator<<(StringPiece str) {
+      if (str.size() > kOutBuf) {
+        Flush();
+        util::WriteOrThrow(fd_, str.data(), str.size());
+      } else {
+        EnsureRemaining(str.size());
+        builder_.AddSubstring(str.data(), str.size());
+      }
+      return *this;
+    }
+
+    // Inefficient!  TODO: more efficient implementation
+    FakeOFStream &operator<<(unsigned value) {
+      return *this << boost::lexical_cast<std::string>(value);
+    }
+
+    FakeOFStream &operator<<(char c) {
+      EnsureRemaining(1);
+      builder_.AddCharacter(c);
+      return *this;
+    }
+
+    // Note this does not sync.
+    void Flush() {
+      util::WriteOrThrow(fd_, buf_.get(), builder_.position());
+      builder_.Reset();
+    }
+
+    // Not necessary, but does assure the data is cleared.
+    void Finish() {
+      Flush();
+      // It will segfault trying to null terminate otherwise.
+      builder_.Finalize();
+      buf_.reset();
+      util::FSyncOrThrow(fd_);
+    }
+
+  private:
+    void EnsureRemaining(std::size_t amount) {
+      if (static_cast<std::size_t>(builder_.size() - builder_.position()) <= amount) {
+        Flush();
+      }
+    }
+
+    util::scoped_malloc buf_;
+    double_conversion::StringBuilder builder_;
+    double_conversion::DoubleToStringConverter convert_;
+    int fd_;
+};
+
+} // namespace