dpb (Function)

Syntax:

Pronunciation:

[ˌdə ˈpib] or [ˌdə ˈpə b] or [ˈdēˈpēˈbē]

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.”