Per the Portal 64 creator in the comments of their Patreon, the library in question was libultra,[1] which is owned and was distributed exclusively by Nintendo but has been extensively pirated.<p>There are open source alternatives, including libdragon[2] and libn64[3]. Not sure how feasible replacing libultra with either of those would be considering the scale of the project.<p>1: <a href="https://n64brew.dev/wiki/Libultra" rel="nofollow">https://n64brew.dev/wiki/Libultra</a><p>2: <a href="https://libdragon.dev/" rel="nofollow">https://libdragon.dev/</a>, <a href="https://github.com/DragonMinded/libdragon">https://github.com/DragonMinded/libdragon</a><p>3: <a href="https://github.com/mikeryan/n64dev/">https://github.com/mikeryan/n64dev/</a>