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The length of an integer x in bits.
NIST SP 800-125B under len(x)
The length of the string x in bits.
NIST SP 800-135 Rev. 1 under len(x)
For a bit string X, len(X) is the length of X in bits.
NIST SP 800-185 under len(X)
The bit length of the bit string X.
NIST SP 800-38F under len(X)
For the non-negative integer x, the bit length of the shortest bit string that can be interpreted as a binary (i.e., base two) representation of the integer x. For integer x > 0, len(x) = ëlog2(x)û + 1. (In the case of 0, len(0) = 1.)