[PATCH 14/16] compat: helper for detecting unsigned overflow
From: Jonathan Nieder <hidden>
Date: 2016-06-15 22:49:45
Subsystem:
the rest · Maintainer:
Linus Torvalds
The idiom (a + b < a) works fine for detecting that an unsigned integer has overflowed, but the 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 this macro with arguments that have side-effects. Signed-off-by: Jonathan Nieder <redacted> --- 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 2af8d3e..817f045 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
--
1.7.2.3