dpb

dpb Function

Syntax:

dpb newbyte bytespec integer → result-integer

Pronunciation:

[ d* pib ] or [ d* p* b ] or [ d—e p—e b—e ]

Arguments and Values:

newbyte—an integer .

bytespec—a byte specifier .

integer—an integer .

result-integer—an integer .

Description:

dpb (deposit byte) is used to replace a field of bits within integer. dpb returns an integer that is the same as integer except in the bits specified by bytespec.

Let s be the size specified by bytespec; then the low s bits of newbyte appear in the result in the byte specified by bytespec. Newbyte is interpreted as being right-justified, as if it were the result of ldb.

Examples:

(dpb 1 (byte 1 10) 0) → 1024 
(dpb -2 (byte 2 10) 0) → 2048 
(dpb 1 (byte 2 10) 2048) → 1024 

See Also:

byte, deposit-field, ldb

Notes:

(logbitp j (dpb m (byte s p) n))

≡ (if (and (>= j p) (< j (+ p s)))

(logbitp (- j p) m)

(logbitp j n))

In general,

(dpb x (byte 0 y) z) ! z

for all valid values of x, y, and z.

Historically, the name “dpb” comes from a DEC PDP-10 assembly language instruction meaning “deposit byte.”

Expanded Reference: dpb

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(dpb )