Plan 9 from Bell Labs’s /usr/web/sources/contrib/anothy/src/lib/djb-ape/byte/case_lowerb.c
#include "case.h" void case_lowerb(char *s,unsigned int len) { unsigned char x; while (len > 0) { --len; x = *s - 'A'; if (x <= 'Z' - 'A') *s = x + 'a'; ++s; } }