Fixed safeguard calculation in ftell().

[pdclib] / functions / stdio / ftell.c

diff --git a/functions/stdio/ftell.c b/functions/stdio/ftell.c
index 63c7f75e1d5de1ebf786a1d9e38e1c9b592a1492..29c360a2fd55d82f1d8569c67c6c3332e5f7fef2 100644 (file)
--- a/functions/stdio/ftell.c
+++ b/functions/stdio/ftell.c
@@ -13,17 +13,6 @@
 
 long int ftell( struct _PDCLIB_file_t * stream )
 {
-    /* If offset is too large for return type, report error instead of wrong
-       offset value.
-       FIXME: A bit too fuzzy in the head right now; stream->ungetidx should be
-       in here somewhere.
-    */
-    if ( stream->pos.offset > ( LONG_MAX - stream->bufidx ) )
-    {
-        /* integer overflow */
-        _PDCLIB_errno = _PDCLIB_EINVAL;
-        return -1;
-    }
     /* ftell() must take into account:
        - the actual *physical* offset of the file, i.e. the offset as recognized
          by the operating system (and stored in stream->pos.offset); and
@@ -39,7 +28,17 @@ long int ftell( struct _PDCLIB_file_t * stream )
            i.e. unprocessed bytes as positive number.
        That is how the somewhat obscure return-value calculation works.
     */
-    return (long int)( stream->pos.offset - ( ( stream->bufend - stream->bufidx ) + stream->ungetidx ) );
+    /*  If offset is too large for return type, report error instead of wrong
+        offset value.
+    */
+    /* TODO: Check what happens when ungetc() is called on a stream at offset 0 */
+    if ( ( stream->pos.offset - stream->bufend ) > ( LONG_MAX - ( stream->bufidx - stream->ungetidx ) ) )
+    {
+        /* integer overflow */
+        _PDCLIB_errno = _PDCLIB_ERANGE;
+        return -1;
+    }
+    return (long int)( stream->pos.offset - ( ( (int)stream->bufend - (int)stream->bufidx ) + stream->ungetidx ) );
 }
 
 #endif