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<title>Using the GNU Compiler Collection (GCC): Long Long</title>

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<a name="Double_002dWord-Integers"></a>
<h3 class="section">6.9 Double-Word Integers</h3>
<a name="index-long-long-data-types"></a>
<a name="index-double_002dword-arithmetic"></a>
<a name="index-multiprecision-arithmetic"></a>
<a name="index-LL-integer-suffix"></a>
<a name="index-ULL-integer-suffix"></a>

<p>ISO C99 supports data types for integers that are at least 64 bits wide,
and as an extension GCC supports them in C90 mode and in C++.
Simply write <code>long long int</code> for a signed integer, or
<code>unsigned long long int</code> for an unsigned integer.  To make an
integer constant of type <code>long long int</code>, add the suffix &lsquo;<samp>LL</samp>&rsquo;
to the integer.  To make an integer constant of type <code>unsigned long
long int</code>, add the suffix &lsquo;<samp>ULL</samp>&rsquo; to the integer.
</p>
<p>You can use these types in arithmetic like any other integer types.
Addition, subtraction, and bitwise boolean operations on these types
are open-coded on all types of machines.  Multiplication is open-coded
if the machine supports a fullword-to-doubleword widening multiply
instruction.  Division and shifts are open-coded only on machines that
provide special support.  The operations that are not open-coded use
special library routines that come with GCC.
</p>
<p>There may be pitfalls when you use <code>long long</code> types for function
arguments without function prototypes.  If a function
expects type <code>int</code> for its argument, and you pass a value of type
<code>long long int</code>, confusion results because the caller and the
subroutine disagree about the number of bytes for the argument.
Likewise, if the function expects <code>long long int</code> and you pass
<code>int</code>.  The best way to avoid such problems is to use prototypes.
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