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| <h3 class="section">6.8 Double-Word Integers</h3> |
| |
| <p><a name="index-g_t_0040code_007blong-long_007d-data-types-2216"></a><a name="index-double_002dword-arithmetic-2217"></a><a name="index-multiprecision-arithmetic-2218"></a><a name="index-g_t_0040code_007bLL_007d-integer-suffix-2219"></a><a name="index-g_t_0040code_007bULL_007d-integer-suffix-2220"></a> |
| 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 ‘<samp><span class="samp">LL</span></samp>’ |
| to the integer. To make an integer constant of type <code>unsigned long |
| long int</code>, add the suffix ‘<samp><span class="samp">ULL</span></samp>’ to the integer. |
| |
| <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 fullword-to-doubleword a 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>There may be pitfalls when you use <code>long long</code> types for function |
| arguments, unless you declare 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 will result because the caller and the |
| subroutine will 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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