FWIW, if you don't have to deal with '\r' only line breaks (do those still exist?), successive calls to strchr or memchr can be much faster than a for loop over characters. The reason is that strchr and memchr are typically already optimized to check a machine word at a time or even using SIMD instructions. If you do have to deal with '\r' only line breaks, it might be worth open-coding the strchr/memchr optimizations, but I never tried.

If you're curious to see the difference, compare the running time of `wc` vs. `wc -l` on large / many files (you might have to force the locale to C for wc -l to hit the fast path).