commit e54e1299404101a5a9d0cf5e45512b543967f958
Author: Mark Adler <madler@alumni.caltech.edu>
Date:   Sat Sep 5 17:45:55 2015 -0700

    Avoid shifts of negative values inflateMark().
    
    The C standard says that bit shifts of negative integers is
    undefined.  This casts to unsigned values to assure a known
    result.

Index: b/src/zlib/inflate.c
===================================================================
--- a/src/zlib/inflate.c
+++ b/src/zlib/inflate.c
@@ -1504,9 +1504,10 @@ z_streamp strm;
 {
     struct inflate_state FAR *state;
 
-    if (strm == Z_NULL || strm->state == Z_NULL) return -1L << 16;
+    if (strm == Z_NULL || strm->state == Z_NULL)
+        return (long)(((unsigned long)0 - 1) << 16);
     state = (struct inflate_state FAR *)strm->state;
-    return ((long)(state->back) << 16) +
+    return (long)(((unsigned long)((long)state->back)) << 16) +
         (state->mode == COPY ? state->length :
             (state->mode == MATCH ? state->was - state->length : 0));
 }