| From e6735556ed0a5e791ea81a015a90c130a0eea060 Mon Sep 17 00:00:00 2001 |
| From: Xi Wang <xi@mit.edu> |
| 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 <xi@mit.edu> |
| Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com> |
| --- |
| 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 |
| |
