ldb extracts and returns the byte of integer specified by bytespec.
ldb returns an integer in which the bits with weights
2^(s - 1) through
2^0 are the same as those in integer with weights
2^(p + s - 1) through
2^p, and all other bits zero;
(byte-size bytespec) and
setf may be used with ldb to modify a byte within the integer that is stored in a given place.
The order of evaluation, when an ldb form is supplied to setf, is exactly left-to-right.
The effect is to perform a dpb operation and then store the result back into the place.
(ldb (byte 2 1) 10)