Fix +loop on 64-bit machines

[pforth] / csrc / pf_inner.c

diff --git a/csrc/pf_inner.c b/csrc/pf_inner.c
index 8ecdec7..7cdaeb1 100644 (file)
--- a/csrc/pf_inner.c
+++ b/csrc/pf_inner.c
@@ -1391,15 +1391,18 @@ DBUG(("XX ah,m,l = 0x%8x,%8x,%8x - qh,l = 0x%8x,%8x\n", ah,am,al, qh,ql ));
 
         case ID_PLUSLOOP_P: /* ( delta -- ) ( R: index limit -- | index limit ) */
             {
 
         case ID_PLUSLOOP_P: /* ( delta -- ) ( R: index limit -- | index limit ) */
             {

-                ucell_t OldIndex, NewIndex, Limit;
-
-                Limit = M_R_POP;
-                OldIndex = M_R_POP;
-                NewIndex = OldIndex + TOS; /* add TOS to index, not 1 */
-/* Do indices cross boundary between LIMIT-1 and LIMIT ? */
-                if( ( (OldIndex - Limit) & ((Limit-1) - NewIndex) & 0x80000000 ) ||
-                    ( (NewIndex - Limit) & ((Limit-1) - OldIndex) & 0x80000000 ) )
-                {
+               cell_t Limit = M_R_POP;
+               cell_t OldIndex = M_R_POP;
+               cell_t Delta = TOS; /* add TOS to index, not 1 */
+               cell_t NewIndex = OldIndex + Delta;
+               cell_t OldDiff = OldIndex - Limit;
+
+               /* This exploits this idea (lifted from Gforth):
+                  (x^y)<0 is equivalent to (x<0) != (y<0) */
+                if( ((OldDiff ^ (OldDiff + Delta)) /* is the limit crossed? */
+                    & (OldDiff ^ Delta))          /* is it a wrap-around? */
+                   < 0 )
+               {

                     InsPtr++;   /* skip branch offset, exit loop */
                 }
                 else
                     InsPtr++;   /* skip branch offset, exit loop */
                 }
                 else