129 lines
7.9 KiB
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129 lines
7.9 KiB
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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN">
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<!Converted with LaTeX2HTML 0.6.5 (Tue Nov 15 1994) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds >
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<HEAD>
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<TITLE>12.10. Implementation Parameters</TITLE>
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<meta name="description" value=" Implementation Parameters">
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<meta name="keywords" value="clm">
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<meta name="resource-type" value="document">
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<meta name="distribution" value="global">
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<P>
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<b>Common Lisp the Language, 2nd Edition</b>
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<BR> <HR><A NAME=tex2html3197 HREF="node135.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html3195 HREF="node121.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html3191 HREF="node133.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html3199 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html3200 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html3198 HREF="node135.html"> Characters</A>
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<B>Up:</B> <A NAME=tex2html3196 HREF="node121.html"> Numbers</A>
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<B> Previous:</B> <A NAME=tex2html3192 HREF="node133.html"> Random Numbers</A>
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<HR> <P>
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<H1><A NAME=SECTION0016100000000000000000>12.10 Implementation Parameters</A></H1>
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<P>
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The values of the named constants defined in this section are
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implementation-dependent. They may be useful for parameterizing
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code in some situations.
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<P>
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<BR><b>[Constant]</b><BR>
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<tt>most-positive-fixnum <BR></tt><tt>most-negative-fixnum</tt><P>The value of <tt>most-positive-fixnum</tt> is that fixnum closest in value to
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positive infinity provided by the implementation.
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<P>
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The value of <tt>most-negative-fixnum</tt> is that fixnum closest in value to
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negative infinity provided by the implementation.
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<P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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X3J13 voted in January 1989
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(FIXNUM-NON-PORTABLE) <A NAME=13813> </A>
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to specify that <tt>fixnum</tt> must be a supertype
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of the type <tt>(signed-byte 16)</tt>, and additionally that the value
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of <tt>array-dimension-limit</tt> must be a fixnum. This implies that the value
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of <tt>most-negative-fixnum</tt> must be less than or equal to <IMG ALIGN=BOTTOM ALT="" SRC="_24769_tex2html_wrap41917.gif">,
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and the value of <tt>most-positive-fixnum</tt> must be greater than or equal to
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both <IMG ALIGN=BOTTOM ALT="" SRC="_24769_tex2html_wrap41919.gif"> and the value of <tt>array-dimension-limit</tt>.
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<BR><b>[Constant]</b><BR>
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<tt>most-positive-short-float <BR></tt><tt>least-positive-short-float <BR></tt><tt>least-negative-short-float <BR></tt><tt>most-negative-short-float</tt><P>The value of <tt>most-positive-short-float</tt> is that short-format
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floating-point number closest in value to (but not equal to)
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positive infinity provided by the implementation.
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<P>
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The value of <tt>least-positive-short-float</tt> is that positive short-format
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floating-point number closest in value to (but not equal to) zero provided by
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the implementation.
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<P>
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The value of <tt>least-negative-short-float</tt> is that negative short-format
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floating-point number closest in value to (but not equal to) zero provided by
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the implementation. (Note that even if an implementation supports
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minus zero as a distinct short floating-point value,
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<tt>least-negative-short-float</tt> must not be minus zero.)
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<P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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X3J13 voted in June 1989 (FLOAT-UNDERFLOW) <A NAME=13830> </A>
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to clarify that these definitions are to be taken quite literally.
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In implementations that support denormalized numbers,
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the values of <tt>least-positive-short-float</tt> and
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<tt>least-negative-short-float</tt> may be denormalized.
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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The value of <tt>most-negative-short-float</tt> is that short-format
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floating-point number closest in value to (but not equal to)
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negative infinity provided by the implementation.
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<P>
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<BR><b>[Constant]</b><BR>
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<tt>most-positive-single-float <BR></tt><tt>least-positive-single-float <BR></tt><tt>least-negative-single-float <BR></tt><tt>most-negative-single-float <BR></tt><tt>most-positive-double-float <BR></tt><tt>least-positive-double-float <BR></tt><tt>least-negative-double-float <BR></tt><tt>most-negative-double-float <BR></tt><tt>most-positive-long-float <BR></tt><tt>least-positive-long-float <BR></tt><tt>least-negative-long-float <BR></tt><tt>most-negative-long-float</tt><P>These are analogous to the constants defined above for short-format
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floating-point numbers.
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<P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif">
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<BR><b>[Constant]</b><BR>
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<tt>least-positive-normalized-short-float <BR></tt><tt>least-negative-normalized-short-float</tt><P>X3J13 voted in June 1989 (FLOAT-UNDERFLOW) <A NAME=13840> </A>
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to add these constants to the language.
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<P>
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The value of <tt>least-positive-normalized-short-float</tt> is that positive normalized
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short-format
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floating-point number closest in value to (but not equal to) zero provided by
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the implementation. In implementations that do not support denormalized numbers
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this may be the same as the value of
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<tt>least-positive-short-float</tt>.
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<P>
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The value of <tt>least-negative-normalized-short-float</tt> is that negative normalized short-format
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floating-point number closest in value to (but not equal to) zero provided by
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the implementation.
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(Note that even if an implementation supports
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minus zero as a distinct short floating-point value,
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<tt>least-negative-normalized-short-float</tt> must not be minus zero.)
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In implementations that do not support denormalized numbers
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this may be the same as the value of <tt>least-positive-short-float</tt>.
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<P>
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<BR><b>[Constant]</b><BR>
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<tt>least-positive-normalized-single-float <BR></tt><tt>least-negative-normalized-single-float <BR></tt><tt>least-positive-normalized-double-float <BR></tt><tt>least-negative-normalized-double-float <BR></tt><tt>least-positive-normalized-long-float <BR></tt><tt>least-negative-normalized-long-float</tt><P>These are analogous to the constants defined above for short-format
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floating-point numbers.
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<BR><b>[Constant]</b><BR>
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<tt>short-float-epsilon <BR></tt><tt>single-float-epsilon <BR></tt><tt>double-float-epsilon <BR></tt><tt>long-float-epsilon</tt><P>These constants have as value, for each floating-point format,
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the smallest positive floating-point number <i>e</i> of that format such that
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the expression
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<P><pre>
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(not (= (float 1 <i>e</i>) (+ (float 1 <i>e</i>) <i>e</i>)))
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</pre><P>
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is true when actually evaluated.
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<P>
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<BR><b>[Constant]</b><BR>
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<tt>short-float-negative-epsilon <BR></tt><tt>single-float-negative-epsilon <BR></tt><tt>double-float-negative-epsilon <BR></tt><tt>long-float-negative-epsilon</tt><P>These constants have as value, for each floating-point format,
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the smallest positive floating-point number <i>e</i> of that format such that
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the expression
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<P><pre>
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(not (= (float 1 <i>e</i>) (- (float 1 <i>e</i>) <i>e</i>)))
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</pre><P>
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is true when actually evaluated.
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<P>
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<P>
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<BR> <HR><A NAME=tex2html3197 HREF="node135.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html3195 HREF="node121.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html3191 HREF="node133.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html3199 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html3200 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html3198 HREF="node135.html"> Characters</A>
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<B>Up:</B> <A NAME=tex2html3196 HREF="node121.html"> Numbers</A>
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<B> Previous:</B> <A NAME=tex2html3192 HREF="node133.html"> Random Numbers</A>
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<HR> <P>
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<HR>
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<P><ADDRESS>
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AI.Repository@cs.cmu.edu
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</ADDRESS>
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