compat: helper for detecting unsigned overflow
The idiom (a + b < a) works fine for detecting that an unsigned
integer has overflowed, but a more explicit
unsigned_add_overflows(a, b)
might be easier to read.
Define such a macro, expanding roughly to ((a) < UINT_MAX - (b)).
Because the expansion uses each argument only once outside of sizeof()
expressions, it is safe to use with arguments that have side effects.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/patch-delta.c b/patch-delta.c
index d218faa..56e0a5e 100644
--- a/patch-delta.c
+++ b/patch-delta.c
@@ -48,7 +48,7 @@
if (cmd & 0x20) cp_size |= (*data++ << 8);
if (cmd & 0x40) cp_size |= (*data++ << 16);
if (cp_size == 0) cp_size = 0x10000;
- if (cp_off + cp_size < cp_size ||
+ if (unsigned_add_overflows(cp_off, cp_size) ||
cp_off + cp_size > src_size ||
cp_size > size)
break;
