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mask-field

mask-field Accessor

Syntax:

mask-field bytespec integer ! masked-integer

(setf (mask-field bytespec place**)** new-masked-integer**)**

Arguments and Values:

bytespec—a byte specifier .

integer—an integer .

masked-integer, new-masked-integer—a non-negative integer .

Description:

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 e↵ect is to perform a deposit-field operation and then store the result back into the place.

Examples:

(mask-field (byte 1 5) -1) *!* 32 
(setq a 15) *!* 15
(mask-field (byte 2 0) a) *!* 3
a *!* 15
(setf (mask-field (byte 2 0) a) 1) *!* 1
a *!* 13

See Also:

byte, ldb

Notes:

(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))

Expanded Reference: mask-field

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(mask-field )