C safe enough to use for parsing untrusted input like this needs to be either formally verified to be safe (not to be correct, at least it's it's the canonical implementation), or written in an intrinsically memory-safe way which humans can fully reason about the safety of. And at that latter point it's slower than Rust. (Not too mention that Rust's awareness of memory lifetimes enables substantial optimizations beyond plain C code that quite often result in faster code at the same level of effort.)

People should learn to use profilers, not even C and C++ do zero overhead versus writing in pure Assembly.

Maybe WEBP should have been written in Assembly, all the speed and I bet quite safe. /s