Recently I tried to make a Zig program that parses and formats some format containing numbers quickly, and I discovered that (after getting rid of all the place

Recently I tried to make a Zig program that parses and formats some format containing numbers quickly, and I discovered that (after getting rid of all the places where one read function would repeatedly call another function that handles arbitrary-sized reads asking for 1 byte) I was spending a lot of time parsing UTF-8 strings to determine their length. This was surprising, because I didn't write any code that's concerned with that sort of thing! It turns out that any time you ask for a formatted value to be padded, the stdlib fmt routines will helpfully format the value, then determine its number of UTF-8 codepoints, then pad it with whatever padding byte you supplied until the number of padding bytes plus the number of UTF-8 codepoints in the formatted value is at least the width you asked for. It will do this even if you were trying to pad a number with zeroes. So now we're compiling against our own stdlib with one line changed to not parse UTF-8 strings when you ask it to format numbers. Luckily none of this stuff cares about locales.