Added a comment.

git-svn-id: svn://svn.cc65.org/cc65/trunk@5769 b7a2c559-68d2-44c3-8de9-860c34a00d81
2024-07-04 13:29:35 +00:00 · 2012-07-07 19:09:23 +00:00 · 2012-07-07 19:09:23 +00:00 · ae42e3b491
commit ae42e3b491
parent a27bc7774e
1 changed files with 5 additions and 0 deletions
--- a/src/cc65/coptshift.c
+++ b/src/cc65/coptshift.c
@ -444,6 +444,11 @@ unsigned OptShift4 (CodeSeg* S)
                 *     dey
                 *     bpl     L1
                 *     rol     a
+                 * 
+                 * A negative shift count or one that is greater or equal than 
+                 * the bit width of the left operand (which is promoted to 
+                 * integer before the operation) causes undefined behaviour, so
+                 * above transformation is safe.
                 */
                CodeLabel* L;