fix another bug or two in 'cmp A B >/dev/null'

[Paul Eggert]

I installed this into diffutils:

2006-05-09  Paul Eggert  <address@hidden>

        * src/cmp.c (cmp): The previous fix wasn't quite right either, as
        it mishandled 'cmp A B >/dev/null' when A is shorter than B and
        differs before A's end-of-file, by outputting a bogus EOF message.
        Also, it was inefficient if A and B were large.

--- src/cmp.c   8 May 2006 01:41:04 -0000       1.44
+++ src/cmp.c   9 May 2006 22:57:06 -0000
@@ -382,7 +382,7 @@ cmp (void)
   word *buffer1 = buffer[1];
   char *buf0 = (char *) buffer0;
   char *buf1 = (char *) buffer1;
-  int ret = EXIT_SUCCESS;
+  int differing = 0;
   int f;
   int offset_width IF_LINT (= 0);
 
@@ -536,17 +536,18 @@ cmp (void)
                  first_diff++;
                }
              while (first_diff < smaller);
+             differing = -1;
+             break;
 
-             /* Fall through.  */
            case type_no_stdout:
-             ret = EXIT_FAILURE;
+             differing = 1;
              break;
            }
        }
 
       if (read0 != read1)
        {
-         if (comparison_type != type_status)
+         if (differing <= 0 && comparison_type != type_status)
            {
              /* See POSIX 1003.1-2001 for this format.  */
              fprintf (stderr, _("cmp: EOF on %s\n"), file[read1 < read0]);
@@ -555,9 +556,9 @@ cmp (void)
          return EXIT_FAILURE;
        }
     }
-  while (read0 == buf_size);
+  while (differing <= 0 && read0 == buf_size);
 
-  return ret;
+  return differing == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 }
 
 /* Compare two blocks of memory P0 and P1 until they differ,