This is a potential security issue, you are being redirected to https://csrc.nist.gov.
A truncation function that outputs the most significant (i.e., leftmost) MacTagBits bits of the input string, X, when the bit length of X is greater than MacTagBits; otherwise, the function outputs X. For example, T2(1011) = 10, T3(1011) = 101, and T4(1011) = 1011.
NIST SP 800-56B Rev. 2