X-Git-Url: https://pd.if.org/git/?a=blobdiff_plain;f=functions%2Fstdio%2Fftell.c;h=e82ca48155e25d22e4fcacfb2f93858e3634f6c9;hb=cc343a7e1383e2f6b8309cb7cb36ab8250586cb4;hp=e392a8b1f01de37121a2683c6a8ab2643f4d326d;hpb=314f0823db6bab83cea91d5712f69b5d83bc575b;p=pdclib.old

diff --git a/functions/stdio/ftell.c b/functions/stdio/ftell.c
index e392a8b..e82ca48 100644
--- a/functions/stdio/ftell.c
+++ b/functions/stdio/ftell.c
@@ -28,18 +28,18 @@ 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.
     */
-    /* If offset is too large for return type, report error instead of wrong
-       offset value. Buffers may not be larger than INT_MAX so the casts are
-       safe.
+    /*  If offset is too large for return type, report error instead of wrong
+        offset value.
     */
-    /* FIXME: This calculation *underflows* when offset smaller than pre-read */
-    if ( ( stream->pos.offset - ( (int)stream->bufend + (int)stream->ungetidx ) ) > ( LONG_MAX - stream->bufidx ) )
+    /* 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 ) );
+    long int res = ( stream->pos.offset - ( ( (int)stream->bufend - (int)stream->bufidx ) + stream->ungetidx ) );
+    return res;
 }
 
 #endif
@@ -63,6 +63,13 @@ int main( void )
     FILE * fh;
     TESTCASE( ( fh = tmpfile() ) != NULL );
     TESTCASE( setvbuf( fh, buffer, _IOLBF, 4 ) == 0 );
+    /* Testing ungetc() at offset 0 */
+    rewind( fh );
+    TESTCASE( ungetc( 'x', fh ) == 'x' );
+    TESTCASE( ftell( fh ) == -1l );
+    rewind( fh );
+    TESTCASE( ftell( fh ) == 0l );
+    /* Commence "normal" tests */
     TESTCASE( fputc( '1', fh ) == '1' );
     TESTCASE( fputc( '2', fh ) == '2' );
     TESTCASE( fputc( '3', fh ) == '3' );