78 lines
4.3 KiB
HTML
78 lines
4.3 KiB
HTML
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<TITLE>CLHS: Function DPB</TITLE>
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<A NAME="dpb"><I>Function</I> <B>DPB</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>dpb</B> <I>newbyte bytespec integer</I> => <I>result-integer</I><P>
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<P>
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<P><B>Pronunciation:</B><P>
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<P>
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[,duh'pib] or [,duh'puhb] or ['dee'pee'bee] <P>
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<P><B>Arguments and Values:</B><P>
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<P>
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<I>newbyte</I>---an <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A>. <P>
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<I>bytespec</I>---a <A REL=DEFINITION HREF="26_glo_b.htm#byte_specifier"><I>byte specifier</I></A>. <P>
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<I>integer</I>---an <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A>. <P>
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<I>result-integer</I>---an <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#dpb"><B>dpb</B></A> (deposit byte) is used to replace a field of bits within <I>integer</I>. <A REL=DEFINITION HREF="#dpb"><B>dpb</B></A> returns an <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A> that is the same as <I>integer</I> except in the bits specified by <I>bytespec</I>. <P>
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Let <TT>s</TT> be the size specified by <I>bytespec</I>; then the low <TT>s</TT> bits of <I>newbyte</I> appear in the result in the byte specified by <I>bytespec</I>. <I>Newbyte</I> is interpreted as being right-justified, as if it were the result of <A REL=DEFINITION HREF="f_ldb.htm#ldb"><B>ldb</B></A>. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(dpb 1 (byte 1 10) 0) => 1024
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(dpb -2 (byte 2 10) 0) => 2048
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(dpb 1 (byte 2 10) 2048) => 1024
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</PRE>
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</TT> <P>
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<P><B>Side Effects:</B> None.
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<P>
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<P><B>Affected By:</B> None.
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<P>
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<P><B>Exceptional Situations:</B> None.
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<P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=DEFINITION HREF="f_by_by.htm#byte"><B>byte</B></A>, <A REL=DEFINITION HREF="f_deposi.htm#deposit-field"><B>deposit-field</B></A>, <A REL=DEFINITION HREF="f_ldb.htm#ldb"><B>ldb</B></A> <P>
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<P><B>Notes:</B><P>
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<P>
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<PRE>
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(logbitp j (dpb m (byte s p) n))
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== (if (and (>= j p) (< j (+ p s)))
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(logbitp (- j p) m)
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(logbitp j n))
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</PRE>
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</TT> <P>
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In general, <P>
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<PRE>
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(dpb x (byte 0 y) z) => z
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</PRE>
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</TT> <P>
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for all valid values of <I>x</I>, <I>y</I>, and <I>z</I>. <P>
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Historically, the name ``dpb'' comes from a DEC PDP-10 assembly language instruction meaning ``deposit byte.'' <P>
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