ConstantTimeByteEq returns 1 if x == y and 0 otherwise.

ConstantTimeCompare returns 1 iff the two equal length slices, x and y, have equal contents.

ConstantTimeCopy copies the contents of y into x iff v == 1.

ConstantTimeEq returns 1 if x == y and 0 otherwise.

ConstantTimeSelect returns x if v is 1 and y if v is 0.