dpb

dpb newbyte bytespec integer → result-integer

[ dϵ pib ] or [ dϵ pϵb ] or [ dē pē bē ]

newbyte — an integer.

bytespec — a byte specifier.

integer — an integer.

result-integer — an integer.

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.

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

byte, deposit-field, ldb

(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.”