ref: 1f6de2fe3823cc6e749b8254187e81e20589bae8
dir: /libkern/utfnlen.c/
#include "lib9.h" int utfnlen(char *s, long m) { int c; long n; Rune rune; char *es; es = s + m; for(n = 0; s < es; n++) { c = *(uchar*)s; if(c < Runeself){ if(c == '\0') break; s++; continue; } if(!fullrune(s, es-s)) break; s += chartorune(&rune, s); } return n; }