64 lines
4.6 KiB
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64 lines
4.6 KiB
HTML
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<TITLE>CLHS: Function ASH</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="f_rati_1.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_number.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="f_intege.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<HR>
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<A NAME="ash"><I>Function</I> <B>ASH</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>ash</B> <I>integer count</I> => <I>shifted-integer</I><P>
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<P>
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<P><B>Arguments and Values:</B><P>
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<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>count</I>---an <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A>. <P>
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<I>shifted-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="#ash"><B>ash</B></A> performs the arithmetic shift operation on the binary representation of <I>integer</I>, which is treated as if it were binary. <P>
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<A REL=DEFINITION HREF="#ash"><B>ash</B></A> shifts <I>integer</I> arithmetically left by <I>count</I> bit positions if <I>count</I> is positive, or right <I>count</I> bit positions if <I>count</I> is negative. The shifted value of the same sign as <I>integer</I> is returned. <P>
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Mathematically speaking, <A REL=DEFINITION HREF="#ash"><B>ash</B></A> performs the computation <TT>floor</TT>(<I>integer</I>*2^<I>count</I>). Logically, <A REL=DEFINITION HREF="#ash"><B>ash</B></A> moves all of the bits in <I>integer</I> to the left, adding zero-bits at the right, or moves them to the right, discarding bits. <P>
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<A REL=DEFINITION HREF="#ash"><B>ash</B></A> is defined to behave as if <I>integer</I> were represented in two's complement form, regardless of how <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integers</I></A> are represented internally. <P><B>Examples:</B><P>
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<PRE>
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(ash 16 1) => 32
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(ash 16 0) => 16
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(ash 16 -1) => 8
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(ash -100000000000000000000000000000000 -100) => -79
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</PRE>
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</TT> <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><P>
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<P>
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Should signal an error of <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> <A REL=DEFINITION HREF="e_tp_err.htm#type-error"><B>type-error</B></A> if <I>integer</I> is not an <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A>. Should signal an error of <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> <A REL=DEFINITION HREF="e_tp_err.htm#type-error"><B>type-error</B></A> if <I>count</I> is not an <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A>. Might signal <A REL=DEFINITION HREF="e_arithm.htm#arithmetic-error"><B>arithmetic-error</B></A>. <P>
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<P><B>See Also:</B> None.
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<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 (ash n k))
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== (and (>= j k) (logbitp (- j k) n))
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</PRE>
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</TT> <HR>
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