[slededit]

"Visibility" is one of the major drivers of promotion in every organization. They don't know your good if they can't see it.

If there are no mitigating circumstances here, like "actually we worked together but I did most of it". Then it should be a simple matter to talk to the boss and get to the bottom of how it was misattributed. No accusations, no assumptions but a fact finding mission. The goal here is to find out how it happened so you can avoid it in the future, and as a secondary bonus it will obviously alert your boss to the fact you are the real author.

If people are able to take credit for your work it indicates a larger problem with your visibility in the organization and it should be dealt with swiftly if you care about your career.

[nuna]

There wasn't collaboration other than plugging it into his code. It was not an oversight it was very clear he claimed to have written it all.You are correct though, partly my fault, why not mention it first myself, why wait for someone else to.

[slededit]

One final suggestion, if when bringing this up you come off as emotional as you do in your original post it won't be effective. Approach it as just a big misunderstanding. There is nothing wrong with ensuring correct attribution to work where its something big (which a library qualifies for).