most platforms come with their own libraries for this, which are usually a mix of hand coded assembly and C. You #include the whole library/sdk, but the lin

most platforms come with their own libraries for this, which are usually a mix of hand coded assembly and C. You #include the whole library/sdk, but the linker strips out all bits you don't use. Even then, if you read the disassembled code, you can usually find within a few minutes looking some stupid/unused/inefficient code - so you could totally do a better job if you wrote the assembly by hand, but it would take much more time (especially since most of these architectures tend to have very irregular instruction sets)