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<h3 class="section">Comparison of Numbers</h3> <p>To test numbers for numerical equality, you should normally use <code>=</code> instead of non-numeric comparison predicates like <code>eq</code>, <code>eql</code> and <code>equal</code>. Distinct floating-point and large integer objects can be numerically equal. If you use <code>eq</code> to compare them, you test whether they are the same <em>object</em>; if you use <code>eql</code> or <code>equal</code>, you test whether their values are <em>indistinguishable</em>. In contrast, <code>=</code> uses numeric comparison, and sometimes returns <code>t</code> when a non-numeric comparison would return <code>nil</code> and vice versa. See <a href="float-basics">Float Basics</a>. </p> <p>In Emacs Lisp, if two fixnums are numerically equal, they are the same Lisp object. That is, <code>eq</code> is equivalent to <code>=</code> on fixnums. It is sometimes convenient to use <code>eq</code> for comparing an unknown value with a fixnum, because <code>eq</code> does not report an error if the unknown value is not a number—it accepts arguments of any type. By contrast, <code>=</code> signals an error if the arguments are not numbers or markers. However, it is better programming practice to use <code>=</code> if you can, even for comparing integers. </p> <p>Sometimes it is useful to compare numbers with <code>eql</code> or <code>equal</code>, which treat two numbers as equal if they have the same data type (both integers, or both floating point) and the same value. By contrast, <code>=</code> can treat an integer and a floating-point number as equal. See <a href="equality-predicates">Equality Predicates</a>. </p> <p>There is another wrinkle: because floating-point arithmetic is not exact, it is often a bad idea to check for equality of floating-point values. Usually it is better to test for approximate equality. Here’s a function to do this: </p> <div class="example"> <pre class="example">(defvar fuzz-factor 1.0e-6)
(defun approx-equal (x y)
(or (= x y)
(< (/ (abs (- x y))
(max (abs x) (abs y)))
fuzz-factor)))
</pre>
</div> <dl> <dt id="=">Function: <strong>=</strong> <em>number-or-marker &rest number-or-markers</em>
</dt> <dd><p>This function tests whether all its arguments are numerically equal, and returns <code>t</code> if so, <code>nil</code> otherwise. </p></dd>
</dl> <dl> <dt id="eql">Function: <strong>eql</strong> <em>value1 value2</em>
</dt> <dd><p>This function acts like <code>eq</code> except when both arguments are numbers. It compares numbers by type and numeric value, so that <code>(eql 1.0 1)</code> returns <code>nil</code>, but <code>(eql 1.0 1.0)</code> and <code>(eql 1 1)</code> both return <code>t</code>. This can be used to compare large integers as well as small ones. Floating-point values with the same sign, exponent and fraction are <code>eql</code>. This differs from numeric comparison: <code>(eql 0.0 -0.0)</code> returns <code>nil</code> and <code>(eql 0.0e+NaN 0.0e+NaN)</code> returns <code>t</code>, whereas <code>=</code> does the opposite. </p></dd>
</dl> <dl> <dt id="/=">Function: <strong>/=</strong> <em>number-or-marker1 number-or-marker2</em>
</dt> <dd><p>This function tests whether its arguments are numerically equal, and returns <code>t</code> if they are not, and <code>nil</code> if they are. </p></dd>
</dl> <dl> <dt id="<">Function: <strong><</strong> <em>number-or-marker &rest number-or-markers</em>
</dt> <dd><p>This function tests whether each argument is strictly less than the following argument. It returns <code>t</code> if so, <code>nil</code> otherwise. </p></dd>
</dl> <dl> <dt id="<=">Function: <strong><=</strong> <em>number-or-marker &rest number-or-markers</em>
</dt> <dd><p>This function tests whether each argument is less than or equal to the following argument. It returns <code>t</code> if so, <code>nil</code> otherwise. </p></dd>
</dl> <dl> <dt id=">">Function: <strong>></strong> <em>number-or-marker &rest number-or-markers</em>
</dt> <dd><p>This function tests whether each argument is strictly greater than the following argument. It returns <code>t</code> if so, <code>nil</code> otherwise. </p></dd>
</dl> <dl> <dt id=">=">Function: <strong>>=</strong> <em>number-or-marker &rest number-or-markers</em>
</dt> <dd><p>This function tests whether each argument is greater than or equal to the following argument. It returns <code>t</code> if so, <code>nil</code> otherwise. </p></dd>
</dl> <dl> <dt id="max">Function: <strong>max</strong> <em>number-or-marker &rest numbers-or-markers</em>
</dt> <dd>
<p>This function returns the largest of its arguments. </p> <div class="example"> <pre class="example">(max 20)
⇒ 20
(max 1 2.5)
⇒ 2.5
(max 1 3 2.5)
⇒ 3
</pre>
</div> </dd>
</dl> <dl> <dt id="min">Function: <strong>min</strong> <em>number-or-marker &rest numbers-or-markers</em>
</dt> <dd>
<p>This function returns the smallest of its arguments. </p> <div class="example"> <pre class="example">(min -4 1)
⇒ -4
</pre>
</div> </dd>
</dl> <dl> <dt id="abs">Function: <strong>abs</strong> <em>number</em>
</dt> <dd><p>This function returns the absolute value of <var>number</var>. </p></dd>
</dl><div class="_attribution">
<p class="_attribution-p">
Copyright © 1990-1996, 1998-2022 Free Software Foundation, Inc. <br>Licensed under the GNU GPL license.<br>
<a href="https://www.gnu.org/software/emacs/manual/html_node/elisp/Comparison-of-Numbers.html" class="_attribution-link">https://www.gnu.org/software/emacs/manual/html_node/elisp/Comparison-of-Numbers.html</a>
</p>
</div>
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