12.2.68 dpb [Function]

dpb newbyte bytespec integer ⇒ result-integer

Pronunciation::

pronounced ,de ’pib or pronounced ,de ’pe b or pronounced ’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.”