SYN_HIST_SIZE
if (count >= SYN_HIST_SIZE) {
a = (history[(count - 2) % SYN_HIST_SIZE] +
history[(count - 1) % SYN_HIST_SIZE]) / 2;
b = (value + history[(count - 1) % SYN_HIST_SIZE]) / 2;
history[(count + 0) % SYN_HIST_SIZE] = value;
int history_x[SYN_MAX_FINGERS][SYN_HIST_SIZE];
int history_y[SYN_MAX_FINGERS][SYN_HIST_SIZE];
int history_z[SYN_MAX_FINGERS][SYN_HIST_SIZE];