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<a name="Negative-Type-Numbers"></a>
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Previous: <a href="Builtin-Type-Descriptors.html#Builtin-Type-Descriptors" accesskey="p" rel="prev">Builtin Type Descriptors</a>, Up: <a href="Builtin-Types.html#Builtin-Types" accesskey="u" rel="up">Builtin Types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Negative-Type-Numbers-1"></a>
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<h4 class="subsection">5.1.3 Negative Type Numbers</h4>
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<p>This is the method used in XCOFF for defining builtin types.
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Since the debugger knows about the builtin types anyway, the idea of
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negative type numbers is simply to give a special type number which
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indicates the builtin type. There is no stab defining these types.
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</p>
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<p>There are several subtle issues with negative type numbers.
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</p>
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<p>One is the size of the type. A builtin type (for example the C types
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<code>int</code> or <code>long</code>) might have different sizes depending on
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compiler options, the target architecture, the ABI, etc. This issue
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doesn’t come up for IBM tools since (so far) they just target the
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RS/6000; the sizes indicated below for each size are what the IBM
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RS/6000 tools use. To deal with differing sizes, either define separate
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negative type numbers for each size (which works but requires changing
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the debugger, and, unless you get both AIX dbx and GDB to accept the
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change, introduces an incompatibility), or use a type attribute
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(see <a href="String-Field.html#String-Field">String Field</a>) to define a new type with the appropriate size
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(which merely requires a debugger which understands type attributes,
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like AIX dbx or GDB). For example,
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</p>
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<div class="example">
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<pre class="example">.stabs "boolean:t10=@s8;-16",128,0,0,0
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</pre></div>
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<p>defines an 8-bit boolean type, and
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</p>
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<div class="example">
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<pre class="example">.stabs "boolean:t10=@s64;-16",128,0,0,0
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</pre></div>
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<p>defines a 64-bit boolean type.
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</p>
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<p>A similar issue is the format of the type. This comes up most often for
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floating-point types, which could have various formats (particularly
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extended doubles, which vary quite a bit even among IEEE systems).
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Again, it is best to define a new negative type number for each
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different format; changing the format based on the target system has
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various problems. One such problem is that the Alpha has both VAX and
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IEEE floating types. One can easily imagine one library using the VAX
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types and another library in the same executable using the IEEE types.
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Another example is that the interpretation of whether a boolean is true
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or false can be based on the least significant bit, most significant
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bit, whether it is zero, etc., and different compilers (or different
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options to the same compiler) might provide different kinds of boolean.
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</p>
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<p>The last major issue is the names of the types. The name of a given
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type depends <em>only</em> on the negative type number given; these do not
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vary depending on the language, the target system, or anything else.
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One can always define separate type numbers—in the following list you
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will see for example separate <code>int</code> and <code>integer*4</code> types
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which are identical except for the name. But compatibility can be
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maintained by not inventing new negative type numbers and instead just
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defining a new type with a new name. For example:
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</p>
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<div class="example">
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<pre class="example">.stabs "CARDINAL:t10=-8",128,0,0,0
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</pre></div>
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<p>Here is the list of negative type numbers. The phrase <em>integral
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type</em> is used to mean twos-complement (I strongly suspect that all
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machines which use stabs use twos-complement; most machines use
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twos-complement these days).
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</p>
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<dl compact="compact">
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<dt><code>-1</code></dt>
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<dd><p><code>int</code>, 32 bit signed integral type.
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</p>
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</dd>
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<dt><code>-2</code></dt>
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<dd><p><code>char</code>, 8 bit type holding a character. Both GDB and dbx on AIX
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treat this as signed. GCC uses this type whether <code>char</code> is signed
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or not, which seems like a bad idea. The AIX compiler (<code>xlc</code>) seems to
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avoid this type; it uses -5 instead for <code>char</code>.
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</p>
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</dd>
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<dt><code>-3</code></dt>
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<dd><p><code>short</code>, 16 bit signed integral type.
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</p>
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</dd>
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<dt><code>-4</code></dt>
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<dd><p><code>long</code>, 32 bit signed integral type.
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</p>
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</dd>
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<dt><code>-5</code></dt>
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<dd><p><code>unsigned char</code>, 8 bit unsigned integral type.
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</p>
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</dd>
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<dt><code>-6</code></dt>
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<dd><p><code>signed char</code>, 8 bit signed integral type.
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</p>
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</dd>
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<dt><code>-7</code></dt>
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<dd><p><code>unsigned short</code>, 16 bit unsigned integral type.
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</p>
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</dd>
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<dt><code>-8</code></dt>
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<dd><p><code>unsigned int</code>, 32 bit unsigned integral type.
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</p>
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</dd>
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<dt><code>-9</code></dt>
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<dd><p><code>unsigned</code>, 32 bit unsigned integral type.
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</p>
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</dd>
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<dt><code>-10</code></dt>
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<dd><p><code>unsigned long</code>, 32 bit unsigned integral type.
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</p>
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</dd>
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<dt><code>-11</code></dt>
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<dd><p><code>void</code>, type indicating the lack of a value.
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</p>
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</dd>
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<dt><code>-12</code></dt>
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<dd><p><code>float</code>, IEEE single precision.
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</p>
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</dd>
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<dt><code>-13</code></dt>
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<dd><p><code>double</code>, IEEE double precision.
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</p>
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</dd>
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<dt><code>-14</code></dt>
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<dd><p><code>long double</code>, IEEE double precision. The compiler claims the size
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will increase in a future release, and for binary compatibility you have
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to avoid using <code>long double</code>. I hope when they increase it they
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use a new negative type number.
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</p>
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</dd>
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<dt><code>-15</code></dt>
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<dd><p><code>integer</code>. 32 bit signed integral type.
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</p>
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</dd>
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<dt><code>-16</code></dt>
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<dd><p><code>boolean</code>. 32 bit type. GDB and GCC assume that zero is false,
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one is true, and other values have unspecified meaning. I hope this
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agrees with how the IBM tools use the type.
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</p>
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</dd>
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<dt><code>-17</code></dt>
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<dd><p><code>short real</code>. IEEE single precision.
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</p>
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</dd>
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<dt><code>-18</code></dt>
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<dd><p><code>real</code>. IEEE double precision.
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</p>
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</dd>
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<dt><code>-19</code></dt>
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<dd><p><code>stringptr</code>. See <a href="Strings.html#Strings">Strings</a>.
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</p>
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</dd>
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<dt><code>-20</code></dt>
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<dd><p><code>character</code>, 8 bit unsigned character type.
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</p>
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</dd>
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<dt><code>-21</code></dt>
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<dd><p><code>logical*1</code>, 8 bit type. This Fortran type has a split
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personality in that it is used for boolean variables, but can also be
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used for unsigned integers. 0 is false, 1 is true, and other values are
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non-boolean.
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</p>
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</dd>
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<dt><code>-22</code></dt>
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<dd><p><code>logical*2</code>, 16 bit type. This Fortran type has a split
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personality in that it is used for boolean variables, but can also be
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used for unsigned integers. 0 is false, 1 is true, and other values are
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non-boolean.
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</p>
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</dd>
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<dt><code>-23</code></dt>
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<dd><p><code>logical*4</code>, 32 bit type. This Fortran type has a split
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personality in that it is used for boolean variables, but can also be
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used for unsigned integers. 0 is false, 1 is true, and other values are
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non-boolean.
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</p>
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</dd>
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<dt><code>-24</code></dt>
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<dd><p><code>logical</code>, 32 bit type. This Fortran type has a split
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personality in that it is used for boolean variables, but can also be
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used for unsigned integers. 0 is false, 1 is true, and other values are
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non-boolean.
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</p>
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</dd>
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<dt><code>-25</code></dt>
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<dd><p><code>complex</code>. A complex type consisting of two IEEE single-precision
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floating point values.
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</p>
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</dd>
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<dt><code>-26</code></dt>
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<dd><p><code>complex</code>. A complex type consisting of two IEEE double-precision
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floating point values.
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</p>
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</dd>
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<dt><code>-27</code></dt>
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<dd><p><code>integer*1</code>, 8 bit signed integral type.
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</p>
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</dd>
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<dt><code>-28</code></dt>
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<dd><p><code>integer*2</code>, 16 bit signed integral type.
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</p>
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</dd>
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<dt><code>-29</code></dt>
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<dd><p><code>integer*4</code>, 32 bit signed integral type.
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</p>
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</dd>
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<dt><code>-30</code></dt>
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<dd><p><code>wchar</code>. Wide character, 16 bits wide, unsigned (what format?
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Unicode?).
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</p>
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</dd>
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<dt><code>-31</code></dt>
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<dd><p><code>long long</code>, 64 bit signed integral type.
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</p>
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</dd>
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<dt><code>-32</code></dt>
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<dd><p><code>unsigned long long</code>, 64 bit unsigned integral type.
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</p>
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</dd>
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<dt><code>-33</code></dt>
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<dd><p><code>logical*8</code>, 64 bit unsigned integral type.
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</p>
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</dd>
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<dt><code>-34</code></dt>
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<dd><p><code>integer*8</code>, 64 bit signed integral type.
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</p></dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Previous: <a href="Builtin-Type-Descriptors.html#Builtin-Type-Descriptors" accesskey="p" rel="prev">Builtin Type Descriptors</a>, Up: <a href="Builtin-Types.html#Builtin-Types" accesskey="u" rel="up">Builtin Types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p>
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