py/objstringio: Fix regression with handling SEEK_SET.

For SEEK_SET, offset should be treated as unsigned, to allow full-width
stream sizes (e.g. 32-bit instead of 31-bit). This is now fully documented
in stream.h. Also, seek symbolic constants are added.

1 files changed, 8 insertions, 0 deletions

diff --git a/py/stream.h b/py/stream.h
index 401ae313c..fbe3d7d85 100644
--- a/py/stream.h
+++ b/py/stream.h
@@ -50,10 +50,18 @@
 
 // Argument structure for MP_STREAM_SEEK
 struct mp_stream_seek_t {
+    // If whence == MP_SEEK_SET, offset should be treated as unsigned.
+    // This allows dealing with full-width stream sizes (16, 32, 64,
+    // etc. bits). For other seek types, should be treated as signed.
     mp_off_t offset;
     int whence;
 };
 
+// seek ioctl "whence" values
+#define MP_SEEK_SET (0)
+#define MP_SEEK_CUR (1)
+#define MP_SEEK_END (2)
+
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_read_obj);
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_read1_obj);
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_readinto_obj);