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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>Hyperlinked ECMA C# Language Specification</title><meta name="author" content="Jon Jagger" /><link rel="stylesheet" href="ecma334.css"></link></head><body><div align="right"><em><a href="http://www.jaggersoft.com">Jon Jagger</a></em></div><div align="right"><a href="mailto:jon@jaggersoft.com">jon@jaggersoft.com</a></div><form method="get" action="http://search.atomz.com/search/"><input size="30" name="sp-q"></input><input type="submit" value="Search C# Spec"></input><input type="hidden" name="sp-a" value="sp10024177"></input><input type="hidden" name="sp-f" value="ISO-8859-1"></input></form><a href="toc.htm">Table of Contents</a> <a href="1.htm">1</a> <a href="2.htm">2</a> <a href="3.htm">3</a> <a href="4.htm">4</a> <a href="5.htm">5</a> <a href="6.htm">6</a> <a href="7.htm">7</a> <a href="8.htm">8</a> <a href="9.htm">9</a> <a href="10.htm">10</a> <a href="11.htm">11</a> <a href="12.htm">12</a> <a href="13.htm">13</a> <a href="14.htm">14</a> <a href="15.htm">15</a> <a href="16.htm">16</a> <a href="17.htm">17</a> <a href="18.htm">18</a> <a href="19.htm">19</a> <a href="20.htm">20</a> <a href="21.htm">21</a> <a href="22.htm">22</a> <a href="23.htm">23</a> <a href="24.htm">24</a> <a href="25.htm">25</a> <a href="notes.htm">Notes</a> <a href="HyperlinkedCSharpECMA.zip">Download</a><span class="ruler"></span><span class="heading">ECMA-334 C# Language Specification</span><span class="navigate"><a href="11.1.4.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="11.1.6.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="10.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="12.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="11.htm">11</a></span><span class="clause-title-previous"> Types</span></span><span class="clause-depth"><a href="11.1.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="11.2.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="11.1.htm">11.1</a></span><span class="clause-title-previous"> Value types</span></span><span class="clause-depth"><a href="11.1.4.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="11.1.6.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">11.1.5</span><span class="clause-title"> Floating point types</span></span><span class="locator">
Paragraph 1</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P1S1"></a>C# supports two floating-point types: <span class="keyword">float</span> and <span class="keyword">double</span>.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P1S2"></a>The <span class="keyword">float</span> and <span class="keyword">double</span> types are represented using the 32-bit single-precision and 64-bit double-precision IEEE 754 formats, which provide the following sets of values: </span><ul><li><span class="sentence"><span class="sentence-number">3</span> <a name="P1S3"></a> Positive zero and negative zero.</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P1S4"></a>In most situations, positive zero and negative zero behave identically as the simple value zero, but certain operations distinguish between the two (<a href="14.7.2.htm">§14.7.2</a>).</span> </li><li><span class="sentence"><span class="sentence-number">5</span> <a name="P1S5"></a> Positive infinity and negative infinity.</span> <span class="sentence"><span class="sentence-number">6</span> <a name="P1S6"></a>Infinities are produced by such operations as dividing a non-zero number by zero.</span> <span class="example">[Example: For example, 1.0 / 0.0 yields positive infinity, and -1.0 / 0.0 yields negative infinity. end example]</span> </li><li><span class="sentence"><span class="sentence-number">7</span> <a name="P1S7"></a> The Not-a-Number value, often abbreviated NaN.</span> <span class="sentence"><span class="sentence-number">8</span> <a name="P1S8"></a>NaNs are produced by invalid floating-point operations, such as dividing zero by zero.</span> </li><li><span class="sentence"><span class="sentence-number">9</span> <a name="P1S9"></a> The finite set of non-zero values of the form s × m × 2<sup>e</sup>, where s is 1 or −1, and m and e are determined by the particular floating-point type: For <span class="keyword">float</span>, 0 < m < 2<sup>24</sup> and −149 ≤ e ≤ 104, and for <span class="keyword">double</span>, 0 < m < 2<sup>53</sup> and −1075 ≤ e ≤ 970.</span> <span class="sentence"><span class="sentence-number">10</span> <a name="P1S10"></a>Denormalized floating-point numbers are considered valid non-zero values.</span> </li></ul></span><span class="locator">
Paragraph 2</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P2S1"></a>The <span class="keyword">float</span> type can represent values ranging from approximately 1.5 × 10<sup>-45</sup> to 3.4 × 10<sup>38</sup> with a precision of 7 digits.</span> </span><span class="locator">
Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>The <span class="keyword">double</span> type can represent values ranging from approximately 5.0 × 10<sup>-324</sup> to 1.7 × 10<sup>308</sup> with a precision of 15-16 digits.</span> </span><span class="locator">
Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>If one of the operands of a binary operator is of a floating-point type, then the other operand must be of an integral type or a floating-point type, and the operation is evaluated as follows: </span><ul><li><span class="sentence"><span class="sentence-number">2</span> <a name="P4S2"></a> If one of the operands is of an integral type, then that operand is converted to the floating-point type of the other operand.</span> </li><li><span class="sentence"><span class="sentence-number">3</span> <a name="P4S3"></a> Then, if either of the operands is of type <span class="keyword">double</span>, the other operand is converted to <span class="keyword">double</span>, the operation is performed using at least <span class="keyword">double</span> range and precision, and the type of the result is <span class="keyword">double</span> (or <span class="keyword">bool</span> for the relational operators).</span> </li><li><span class="sentence"><span class="sentence-number">4</span> <a name="P4S4"></a> Otherwise, the operation is performed using at least <span class="keyword">float</span> range and precision, and the type of the result is <span class="keyword">float</span> (or <span class="keyword">bool</span> for the relational operators).</span> </li></ul></span><span class="locator">
Paragraph 5</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P5S1"></a>The floating-point operators, including the assignment operators, never produce exceptions.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P5S2"></a>Instead, in exceptional situations, floating-point operations produce zero, infinity, or NaN, as described below: </span><ul><li><span class="sentence"><span class="sentence-number">3</span> <a name="P5S3"></a> If the result of a floating-point operation is too small for the destination format, the result of the operation becomes positive zero or negative zero.</span> </li><li><span class="sentence"><span class="sentence-number">4</span> <a name="P5S4"></a> If the result of a floating-point operation is too large for the destination format, the result of the operation becomes positive infinity or negative infinity.</span> </li><li><span class="sentence"><span class="sentence-number">5</span> <a name="P5S5"></a> If a floating-point operation is invalid, the result of the operation becomes NaN.</span> </li><li><span class="sentence"><span class="sentence-number">6</span> <a name="P5S6"></a> If one or both operands of a floating-point operation is NaN, the result of the operation becomes NaN.</span> </li></ul></span><span class="locator">
Paragraph 6</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P6S1"></a>Floating-point operations may be performed with higher precision than the result type of the operation.</span> <span class="example">[Example: For example, some hardware architectures support an "extended" or "long double" floating-point type with greater range and precision than the <span class="keyword">double</span> type, and implicitly perform all floating-point operations using this higher precision type. Only at excessive cost in performance can such hardware architectures be made to perform floating-point operations with less precision, and rather than require an implementation to forfeit both performance and precision, C# allows a higher precision type to be used for all floating-point operations. Other than delivering more precise results, this rarely has any measurable effects. However, in expressions of the form x * y / z, where the multiplication produces a result that is outside the <span class="keyword">double</span> range, but the subsequent division brings the temporary result back into the <span class="keyword">double</span> range, the fact that the expression is evaluated in a higher range format may cause a finite result to be produced instead of an infinity. end example]</span> </span><span class="ruler"></span><table><tr><td><table align="left" bgcolor="navy"><tr bgcolor="navy"><td><font face="Arial,sans-serif" size="6" color="yellow"><strong>{ JSL }</strong></font></td></tr></table></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>Jagger Software Ltd</strong></font></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>Company # 4070126</strong></font></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>VAT # 762 5213 42</strong></font></td></tr></table><img src="valid-html401.png" align="left" height="31" width="88" alt="Valid HTML 4.01" /><img src="vcss.gif" align="left" height="31" width="88" alt="Valid CSS" /></body></html>⌨️ 快捷键说明
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