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| author | Jonathan Nieder <jrnieder@gmail.com> | 2010-10-11 02:59:26 (GMT) |
|---|---|---|
| committer | Junio C Hamano <gitster@pobox.com> | 2011-02-10 21:47:56 (GMT) |
| commit | 1368f65002bf39fdde7dd736a75ae35475184371 (patch) | |
| tree | cb0d57165c5b1f710bb5e6499fa322185a8deb2f /git-compat-util.h | |
| parent | a8e4a5943a63c8fd4a3a9b70ccf4608bcc973707 (diff) | |
| download | git-1368f65002bf39fdde7dd736a75ae35475184371.zip git-1368f65002bf39fdde7dd736a75ae35475184371.tar.gz git-1368f65002bf39fdde7dd736a75ae35475184371.tar.bz2 | |
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>
Diffstat (limited to 'git-compat-util.h')
| -rw-r--r-- | git-compat-util.h | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/git-compat-util.h b/git-compat-util.h index d6d269f..9c23622 100644 --- a/git-compat-util.h +++ b/git-compat-util.h @@ -31,6 +31,9 @@ #define maximum_signed_value_of_type(a) \ (INTMAX_MAX >> (bitsizeof(intmax_t) - bitsizeof(a))) +#define maximum_unsigned_value_of_type(a) \ + (UINTMAX_MAX >> (bitsizeof(uintmax_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. @@ -40,6 +43,9 @@ #define signed_add_overflows(a, b) \ ((b) > maximum_signed_value_of_type(a) - (a)) +#define unsigned_add_overflows(a, b) \ + ((b) > maximum_unsigned_value_of_type(a) - (a)) + #ifdef __GNUC__ #define TYPEOF(x) (__typeof__(x)) #else |