how fastread function is faster than scanf function?

please tell me that how fastread function performs faster than scanf here is the code for fastread

inline void fastread(int* a)
{
    register char c = 0;
    while (c < 33)
        c = getchar();
    *a = 0;
    while (c > 33)
    {
        *a = *a * 10 + c - '0';
        c = getchar();
    }
}