S_SIZE
#define V_SIZE(x) ((x) << S_SIZE)
#define G_SIZE(x) (((x) >> S_SIZE) & M_SIZE)
char buf[S_SIZE + 1];
if (likely(m->count < S_SIZE)) {
len = vsnprintf(m->buf + m->count, S_SIZE - m->count, f, args);
if (likely(m->count + len < S_SIZE)) {
m->count = S_SIZE;