Attempt to fix one path through copy bits. I think this works,

but I make no claims about understanding why.

diff --git a/v7/src/microcode/bitstr.c b/v7/src/microcode/bitstr.c
index 28c541811c4ce43ee07ce7d15fb6217f1ea6e804..0a829a3d1264a483123185ec9fc0dfb46275db69 100644 (file)
--- a/v7/src/microcode/bitstr.c
+++ b/v7/src/microcode/bitstr.c
@@ -30,7 +30,7 @@ Technology nor of any adaptation thereof in any advertising,
 promotional, or sales literature without prior written consent from
 MIT in each case. */
 
-/* $Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/microcode/bitstr.c,v 9.36 1987/11/23 05:13:53 cph Rel $
+/* $Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/microcode/bitstr.c,v 9.37 1988/06/08 16:05:31 jrm Exp $
 
    Bit string primitives. 
 
@@ -591,12 +591,27 @@ copy_bits (source, source_offset, destination, destination_offset, nbits)
            tail = (nbits % POINTER_LENGTH);
            if (tail <= offset1)
              {
+               long mask;
+
+               mask = (any_mask (tail, (offset1 - tail)));
+
+
+               /* This path through copy bits didn't work in certain
+                  cases.  The line below seems to fix it.  This was an
+                  empirical test, and I don't understand it enough to
+                  tell if it is correct, but I think it is, and I did
+                  a few tests.  This is probably what is broken if you
+                  are here poking around trying to fix something.
+                  ~JRM
+                */
+               dest_buffer &= (~ mask);
+
                (bit_string_word (destination)) =
                  (dest_buffer |
                   ((bit_string_word (destination)) &
                    (low_mask (offset1 - tail))) |
                   (((bit_string_word (source)) >> offset2) &
-                   (any_mask (tail, (offset1 - tail)))));
+                   mask));
              }
            else
              {