From e6735556ed0a5e791ea81a015a90c130a0eea060 Mon Sep 17 00:00:00 2001 From: Xi Wang Date: Wed, 20 Feb 2013 12:45:45 -0500 Subject: [PATCH] nice: fix overflow checking in int_add_no_wrap() In C, signed integer overflow is undefined behavior. Many compilers optimize away checks like `a + b < a'. Use safe precondition testing instead. Signed-off-by: Xi Wang Signed-off-by: Bernhard Reutner-Fischer --- libc/sysdeps/linux/common/nice.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/libc/sysdeps/linux/common/nice.c b/libc/sysdeps/linux/common/nice.c index 3694db8..ed39946 100644 --- a/libc/sysdeps/linux/common/nice.c +++ b/libc/sysdeps/linux/common/nice.c @@ -25,15 +25,15 @@ static __inline__ _syscall1(int, __syscall_nice, int, incr) static __inline__ int int_add_no_wrap(int a, int b) { - int s = a + b; - if (b < 0) { - if (s > a) s = INT_MIN; + if (a < INT_MIN - b) + return INT_MIN; } else { - if (s < a) s = INT_MAX; + if (a > INT_MAX - b) + return INT_MAX; } - return s; + return a + b; } static __inline__ int __syscall_nice(int incr) -- 1.7.10.4