262 lines
5.4 KiB
HTML
262 lines
5.4 KiB
HTML
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<!DOCTYPE HTML>
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<HTML LANG="en-us"
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><HEAD
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><TITLE
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>logcount | Common Lisp Nova Spec</TITLE
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><META CHARSET="US-ASCII"
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><LINK REL="canonical" HREF="f_logcount.html"
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><LINK REL="next" HREF="f_logtest.html" TYPE="text/html" TITLE="logtest"
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><LINK REL="prev" HREF="f_logbitp.html" TYPE="text/html" TITLE="logbitp"
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><LINK REL="up" HREF="12_2_Numbers_Dictionary.html" TYPE="text/html" TITLE="12.2 Numbers Dictionary"
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><LINK REL="start" HREF="index.html" TYPE="text/html" TITLE="Common Lisp Nova Spec"
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><META NAME="VIEWPORT" CONTENT="width=device-width, initial-scale=1.0"
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><LINK REL="STYLESHEET" HREF="dpans.css%3F3909942064.css"
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><SCRIPT SRC="dpans.js%3F3909942064"
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></SCRIPT
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><SCRIPT SRC="apropos.js%3F3909942064"
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></SCRIPT
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></HEAD
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><BODY
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><DIV
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><DIV CLASS="topnav"
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><DIV CLASS="breadcrumb"
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><SPAN CLASS="breadcrumb-item"
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><A HREF="index.html"
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>Common Lisp Nova Spec</A
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></SPAN
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="12_Numbers.html"
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>12. Numbers</A
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></SPAN
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="12_2_Numbers_Dictionary.html"
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>12.2 Numbers Dictionary</A
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></SPAN
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="f_logcount.html"
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>logcount</A
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></SPAN
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></DIV
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><DIV CLASS="apropos"
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><DIV CLASS="apropos-io"
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><A HREF="f_logbitp.html" CLASS="prev"
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>←</A
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><SPAN ID="apropos-label"
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>Apropos </SPAN
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><INPUT ID="apropos" AUTOFOCUS="AUTOFOCUS" PLACEHOLDER="Type here to search" ONINPUT="aproposInput(this);" ONKEYUP="aproposKeyup(event);" ONCHANGE="aproposChange(this);" ONFOCUS="aproposFocus(this);" ONFOCUSOUT="aproposFocusout(this);"
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><A HREF="f_logtest.html" CLASS="next"
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>→</A
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></DIV
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><DIV ID="apropos-res"
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></DIV
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></DIV
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></DIV
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><DIV CLASS="matter"
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><DIV CLASS="com"
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><DIV CLASS="begincom"
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><HR
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><TABLE WIDTH="100%" CELLSPACING="0" CELLPADDING="0"
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><TR
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><TD ALIGN="LEFT" VALIGN="BASELINE" WIDTH="100%" CLASS="name"
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><SPAN CLASS="idx" DATA-KIND="idxref" DATA-TERM="logcount"
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></SPAN
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><B
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>logcount</B
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></TD
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><TD ALIGN="RIGHT" VALIGN="BASELINE" WIDTH="0" NOWRAP="NOWRAP" CLASS="ftype"
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><I
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>Function</I
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></TD
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></TR
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></TABLE
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><HR
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></DIV
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><UL CLASS="subtoc"
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></UL
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><DL
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><DT
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><B
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>Syntax</B
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></DT
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><DD
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><P CLASS="j"
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><B
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>logcount</B
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> <SPAN CLASS="cmssi"
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>integer</SPAN
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> <SPAN CLASS="arrow"
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>→</SPAN
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> <SPAN CLASS="cmssi"
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>number-of-on-bits</SPAN
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></P
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></DD
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><DT
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><B
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>Arguments and Values</B
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></DT
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><DD
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><P CLASS="j"
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><VAR CLASS="param"
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>integer</VAR
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> — an <A HREF="26_1_Glossary.html#integer"
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><EM CLASS="term"
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>integer</EM
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></A
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>. </P
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><P CLASS="j"
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><VAR CLASS="param"
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>number-of-on-bits</VAR
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> — a non-negative <A HREF="26_1_Glossary.html#integer"
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><EM CLASS="term"
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>integer</EM
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></A
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>.</P
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></DD
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><DT
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><B
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>Description</B
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></DT
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><DD
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><P CLASS="j"
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>Computes and returns the number of bits in the two’s-complement binary representation of <VAR CLASS="param"
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>integer</VAR
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> that are ‘on’ or ‘set’. If <VAR CLASS="param"
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>integer</VAR
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> is negative, the <CODE CLASS="f"
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>0</CODE
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> bits are counted; otherwise, the <CODE CLASS="f"
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>1</CODE
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> bits are counted.</P
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></DD
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><DT
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><B
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>Examples</B
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></DT
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><DD
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><PRE CLASS="screen"
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>(logcount 0) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 0
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(logcount -1) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 0
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(logcount 7) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 3
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(logcount 13) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 3 ;Two's-complement binary: ...0001101
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(logcount -13) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 2 ;Two's-complement binary: ...1110011
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(logcount 30) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 4 ;Two's-complement binary: ...0011110
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(logcount -30) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 4 ;Two's-complement binary: ...1100010
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(logcount (expt 2 100)) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 1
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(logcount (- (expt 2 100))) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 100
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(logcount (- (1+ (expt 2 100)))) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 1</PRE
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></DD
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><DT
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><B
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>Exceptional Situations</B
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></DT
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><DD
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><P CLASS="j"
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>Should signal <A HREF="t_type-error.html" CLASS="typeref"
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><B
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>type-error</B
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></A
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> if its argument is not an <A HREF="26_1_Glossary.html#integer"
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><EM CLASS="term"
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>integer</EM
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></A
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>.</P
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></DD
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><DT
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><B
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>Notes</B
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></DT
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><DD
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><P CLASS="j"
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>Even if the <A HREF="26_1_Glossary.html#implementation"
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><EM CLASS="term"
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>implementation</EM
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></A
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> does not represent <A HREF="26_1_Glossary.html#integer"
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><EM CLASS="term"
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>integers</EM
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></A
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> internally in two’s complement binary, <A HREF="f_logcount.html" CLASS="funref"
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><B
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>logcount</B
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></A
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> behaves as if it did. </P
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><P CLASS="j"
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>The following identity always holds:</P
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><PRE CLASS="screen"
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> (logcount <VAR CLASS="param"
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>x</VAR
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>)
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<SPAN CLASS="cmsy"
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><SPAN STYLE="font-size:16px;vertical-align:-2px"
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>≡</SPAN
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></SPAN
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> (logcount (- (+ <VAR CLASS="param"
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>x</VAR
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> 1)))
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<SPAN CLASS="cmsy"
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><SPAN STYLE="font-size:16px;vertical-align:-2px"
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>≡</SPAN
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></SPAN
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> (logcount (lognot <VAR CLASS="param"
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>x</VAR
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>))</PRE
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></DD
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></DL
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></DIV
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></DIV
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><DIV CLASS="footer"
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><DIV CLASS="btmnav"
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><A HREF="f_logbitp.html" CLASS="prev"
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>←</A
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><A HREF="f_logtest.html" CLASS="next"
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>→</A
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></DIV
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><DIV CLASS="trail"
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>Conversion to HTML copyright 2023 by Gilbert Baumann</DIV
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></DIV
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></DIV
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><SCRIPT
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>domReady();</SCRIPT
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></BODY
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></HTML
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>
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