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do not depend on signed integer overflow

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Signed integer overflow is not defined in C, so do not depend on it.

This fixes a problem with GCC 4.4.0 and -O3 where the optimizer would
consider "consumed_bytes > consumed_bytes + bytes" as a constant
expression, and never execute the die()-call.

Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Erik Faye-Lund 2010-10-05 09:24:10 +02:00 committed by Junio C Hamano
parent b90d9b8895
commit c03c83152d
4 changed files with 15 additions and 3 deletions
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2
builtin/index-pack.c
View File

@ -161,7 +161,7 @@ static void use(int bytes)
input_offset += bytes;
/* make sure off_t is sufficiently large not to wrap */
if (consumed_bytes > consumed_bytes + bytes)
if (signed_add_overflows(consumed_bytes, bytes))
die("pack too large for current definition of off_t");
consumed_bytes += bytes;
}

2
builtin/pack-objects.c
View File

@ -431,7 +431,7 @@ static int write_one(struct sha1file *f,
written_list[nr_written++] = &e->idx;
/* make sure off_t is sufficiently large not to wrap */
if (*offset > *offset + size)
if (signed_add_overflows(*offset, size))
die("pack too large for current definition of off_t");
*offset += size;
return 1;

2
builtin/unpack-objects.c
View File

@ -83,7 +83,7 @@ static void use(int bytes)
offset += bytes;
/* make sure off_t is sufficiently large not to wrap */
if (consumed_bytes > consumed_bytes + bytes)
if (signed_add_overflows(consumed_bytes, bytes))
die("pack too large for current definition of off_t");
consumed_bytes += bytes;
}

12
git-compat-util.h
View File

@ -28,6 +28,18 @@
#define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))
#define bitsizeof(x) (CHAR_BIT * sizeof(x))
#define maximum_signed_value_of_type(a) \
(INTMAX_MAX >> (bitsizeof(intmax_t) - bitsizeof(a)))
/*
* Signed integer overflow is undefined in C, so here's a helper macro
* to detect if the sum of two integers will overflow.
*
* Requires: a >= 0, typeof(a) equals typeof(b)
*/
#define signed_add_overflows(a, b) \
((b) > maximum_signed_value_of_type(a) - (a))
#ifdef __GNUC__
#define TYPEOF(x) (__typeof__(x))
#else