I would not know how to add them up, the 2 types you mentioned are relatively low quality sources, a general rule is the easier it is to get a link, the less ranking value it provides, there are automated tools to speed getting social bookmarks and directory submissions. Things like in body links in articles discussing your site's topic, particularly from a higher ranked site is seen as less prone to being spam. Getting to know an influential blogger by first writing thoughtful comments may help you get to write a guest article including as link to your site, that sort of hard earned link tends to be more valuable.
Blog comments and forum post signatures are also in the lower grade, easy to obtain class. Article directory sites like Ezinearticles mat provide slightly better links, though some say the direct traffic they generate is the most valuable result, in addition to the directory site backlink, sites republishing a good article provide more links.
In addition to the source type and it's page rank and the number of other links on the page, whether the links are NoFollow and whether they have anchor text effect the value of the link. Some links are 1000x more powerful than others.
Getting links from a diversity of sources is important to look natural, ant links believed to be created just to get ranking are ignored.