line-reader: Fix bad math when size_t is bigger than off_t.

When size_t is bigger than off_t, pos - r->length will end up very large,
instead of negative, when r->length > pos, so the MAX didn't help to get
rid of negative values.  I'm not sure that this should really happen in
practice, but it's better to avoid it.

Reported by GCC on x86-64.

diff --git a/src/libpspp/line-reader.c b/src/libpspp/line-reader.c
index 6f90b502cd856dd64db366ce1bb36561141648f0..56a368da2965f08f6c7d9c43aa69ae5cfca155d9 100644 (file)
--- a/src/libpspp/line-reader.c
+++ b/src/libpspp/line-reader.c
@@ -1,5 +1,5 @@
 /* PSPP - a program for statistical analysis.
-   Copyright (C) 2010, 2011 Free Software Foundation, Inc.
+   Copyright (C) 2010, 2011, 2014 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -311,9 +311,9 @@ off_t
 line_reader_tell (const struct line_reader *r)
 {
   off_t pos = lseek (r->fd, 0, SEEK_CUR);
-  if (pos >= 0)
-    pos = MAX (0, pos - r->length);
-  return pos;
+  return (pos < 0 ? pos
+          : pos >= r->length ? pos - r->length
+          : 0);
 }
 
 /* Returns true if end of file has been encountered reading R. */