Function posrelat

Source/Misc/lua/src/lua.c:13713–13717

static ptrdiff_t posrelat (ptrdiff_t pos, size_t len) {
/* relative string position: negative means back from end */
if (pos < 0) pos += (ptrdiff_t)len + 1;
return (pos >= 0) ? pos : 0;
}


static int str_sub (lua_State *L) {