Avoid shifts of negative values inflateMark().

madler · madler · commit e54e12994041 · 2015-09-05T17:45:55.000-07:00
The C standard says that bit shifts of negative integers is
undefined.  This casts to unsigned values to assure a known
result.
diff --git a/inflate.c b/inflate.c
@@ -1506,9 +1506,10 @@ 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));
 }

Original file line number	Diff line number	Diff line change
`@@ -1506,9 +1506,10 @@ z_streamp strm;`
`1506`	`1506`	`{`
`1507`	`1507`	`struct inflate_state FAR *state;`
`1508`	`1508`
`1509`		`- if (strm == Z_NULL \|\| strm->state == Z_NULL) return -1L << 16;`
	`1509`	`+ if (strm == Z_NULL \|\| strm->state == Z_NULL)`
	`1510`	`+ return (long)(((unsigned long)0 - 1) << 16);`
`1510`	`1511`	`state = (struct inflate_state FAR *)strm->state;`
`1511`		`- return ((long)(state->back) << 16) +`
	`1512`	`+ return (long)(((unsigned long)((long)state->back)) << 16) +`
`1512`	`1513`	`(state->mode == COPY ? state->length :`
`1513`	`1514`	`(state->mode == MATCH ? state->was - state->length : 0));`
`1514`	`1515`	`}`