Eric Dumazet wrote, On 12/14/2007 12:09 PM: ... > + /* > + * Instead of returning hash % ht->cfg.size (implying a divide) > + * we return the high 32 bits of the (hash * ht->cfg.size) that will > + * give results between [0 and cfg.size-1] and same hash distribution, > + * but using a multiply, less expensive than a divide > + */ > + return ((u64)hash * ht->cfg.size) >> 32;
Are we sure of the same hash distribution? Probably I miss something, but: if this 'hash' is well distributed on 32 bits, and ht->cfg.size is smaller than 32 bits, e.g. 256 (8 bits), then this multiplication moves to the higher 32 of u64 only max. 8 bits of the most significant byte, and the other three bytes are never used, while division is always affected by all four bytes... Regards, Jarek P. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
