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compat: helper for detecting unsigned overflow

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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>
This commit is contained in:
Jonathan Nieder
2010-10-10 21:59:26 -05:00
committed by Junio C Hamano
parent a8e4a5943a
commit 1368f65002
4 changed files with 11 additions and 4 deletions
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patch-delta.c
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@@ -48,7 +48,7 @@ void *patch_delta(const void *src_buf, unsigned long src_size,
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;