qsort() ptrdiff_t may be larger than int

Junio C Hamano · Junio C Hamano · commit e23eff8be92a · 2005-12-06T17:28:26.000-08:00
Morten Welinder &lt;mwelinder@gmail.com&gt; writes:

&gt; The code looks wrong.  It assumes that pointers are no larger than ints.
&gt; If pointers are larger than ints, the code does not necessarily compute
&gt; a consistent ordering and qsort is allowed to do whatever it wants.
&gt;
&gt; Morten
&gt;
&gt; static int compare_object_pointers(const void *a, const void *b)
&gt; {
&gt; 	const struct object * const *pa = a;
&gt; 	const struct object * const *pb = b;
&gt; 	return *pa - *pb;
&gt; }

Signed-off-by: Junio C Hamano &lt;junkio@cox.net&gt;
diff --git a/object.c b/object.c
@@ -82,7 +82,12 @@ static int compare_object_pointers(const void *a, const void *b)
 {
 	const struct object * const *pa = a;
 	const struct object * const *pb = b;
-	return *pa - *pb;
+	if (*pa == *pb)
+		return 0;
+	else if (*pa < *pb)
+		return -1;
+	else
+		return 1;
 }
 
 void set_object_refs(struct object *obj, struct object_refs *refs)

Original file line number	Diff line number	Diff line change
`@@ -82,7 +82,12 @@ static int compare_object_pointers(const void a, const void b)`
`82`	`82`	`{`
`83`	`83`	`const struct object * const *pa = a;`
`84`	`84`	`const struct object * const *pb = b;`
`85`		`- return pa - pb;`
	`85`	`+ if (pa == pb)`
	`86`	`+ return 0;`
	`87`	`+ else if (pa < pb)`
	`88`	`+ return -1;`
	`89`	`+ else`
	`90`	`+ return 1;`
`86`	`91`	`}`
`87`	`92`
`88`	`93`	`void set_object_refs(struct object obj, struct object_refs refs)`