• mask-field bytespec integer → masked-integer (setf (mask-field bytespec place) new-masked-integer)

• bytespec - a byte specifier.
• integer - an integer.
• masked-integer, new-masked-integer - a non-negative integer.

mask-field performs a "mask" operation on integer. It returns an integer that has the same bits as integer in the byte specified by bytespec, but that has zero-bits everywhere else.

setf may be used with mask-field to modify a byte within the integer that is stored in a given place. The effect is to perform a deposit-field operation and then store the result back into the place.

(mask-field (byte 1 5) -1) 

→

32 



(defparameter *a* 15) 

→

15 



(mask-field (byte 2 0) *a*) 

→

3 



*a* 

→

15 



(setf (mask-field (byte 2 0) *a*) 1) 

→

1 



*a* 

→

13

None.

None.

None.

• Function BYTE
• Function LDB

(ldb bs (mask-field bs n)) 
  ≡ (ldb bs n)
(logbitp j (mask-field (byte s p) n)) 
  ≡ (and (>= j p) 
         (< j s) 
         (logbitp j n)) 
(mask-field bs n) 
  ≡ (logand n (dpb -1 bs 0))