diff options
Diffstat (limited to 'net/batman-adv/main.h')
| -rw-r--r-- | net/batman-adv/main.h | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/net/batman-adv/main.h b/net/batman-adv/main.h index 0150897acf63..80be5ad4fc9c 100644 --- a/net/batman-adv/main.h +++ b/net/batman-adv/main.h @@ -182,4 +182,20 @@ static inline int compare_eth(const void *data1, const void *data2) #define atomic_dec_not_zero(v) atomic_add_unless((v), -1, 0) +/* Returns the smallest signed integer in two's complement with the sizeof x */ +#define smallest_signed_int(x) (1u << (7u + 8u * (sizeof(x) - 1u))) + +/* Checks if a sequence number x is a predecessor/successor of y. + * they handle overflows/underflows and can correctly check for a + * predecessor/successor unless the variable sequence number has grown by + * more then 2**(bitwidth(x)-1)-1. + * This means that for a uint8_t with the maximum value 255, it would think: + * - when adding nothing - it is neither a predecessor nor a successor + * - before adding more than 127 to the starting value - it is a predecessor, + * - when adding 128 - it is neither a predecessor nor a successor, + * - after adding more than 127 to the starting value - it is a successor */ +#define seq_before(x, y) ({typeof(x) _dummy = (x - y); \ + _dummy > smallest_signed_int(_dummy); }) +#define seq_after(x, y) seq_before(y, x) + #endif /* _NET_BATMAN_ADV_MAIN_H_ */ |