add macOS implementation

macos/src/StreamBufferAdapter.cpp

@@ -0,0 +1,83 @@
+#include <streambuf>
+#include <functional>
+#include <cassert>
+#include <cstring>
+
+using namespace std;
+
+namespace polyvox {
+
+class StreamBufferAdapter : public std::streambuf
+{
+    public:
+        StreamBufferAdapter(const char *begin, const char *end);
+        ~StreamBufferAdapter() {
+          
+        }
+        streamsize size();
+        
+    private:
+        int_type uflow() override;
+        int_type underflow() override;
+        int_type pbackfail(int_type ch) override;
+        streampos seekoff(streamoff off, ios_base::seekdir way, ios_base::openmode which) override;
+        streampos seekpos(streampos sp, ios_base::openmode which) override;
+        std::streamsize showmanyc() override;
+        
+};
+
+StreamBufferAdapter::StreamBufferAdapter(const char *begin, const char *end)
+{
+    setg((char*)begin, (char*)begin, (char*)end);
+}
+
+streamsize StreamBufferAdapter::size() {
+  return egptr() - eback();
+}
+
+streambuf::int_type StreamBufferAdapter::underflow()
+{
+    if (gptr() == egptr()) {
+        return traits_type::eof();
+    }
+    return *(gptr());
+}
+
+streambuf::int_type StreamBufferAdapter::uflow()
+{
+    if (gptr() == egptr()) {
+        return traits_type::eof();
+    }
+    gbump(1);
+
+    return *(gptr());
+}
+
+streambuf::int_type StreamBufferAdapter::pbackfail(int_type ch)
+{
+    if (gptr() ==  eback() || (ch != traits_type::eof() && ch != gptr()[-1]))
+        return traits_type::eof();
+    gbump(-ch);
+    return *(gptr());
+}
+
+streamsize StreamBufferAdapter::showmanyc()
+{
+    return egptr() - gptr();
+}
+
+streampos StreamBufferAdapter::seekoff(streamoff off, ios_base::seekdir way, ios_base::openmode which = ios_base::in) {
+  if(way == ios_base::beg) {
+    setg(eback(), eback()+off, egptr());
+  } else if(way == ios_base::cur) {
+    gbump(off);
+  } else {
+    setg(eback(), egptr()-off, egptr());
+  }
+  return gptr() - eback();
+}
+
+streampos StreamBufferAdapter::seekpos(streampos sp, ios_base::openmode which = ios_base::in) {
+    return seekoff(sp - pos_type(off_type(0)), std::ios_base::beg, which);
+}
+}