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| <h3 class="section">4.7 Arrays and pointers</h3> |
| |
| <ul> |
| <li><cite>The result of converting a pointer to an integer or |
| vice versa (C90 6.3.4, C99 6.3.2.3).</cite> |
| |
| <p>A cast from pointer to integer discards most-significant bits if the |
| pointer representation is larger than the integer type, |
| sign-extends<a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a> |
| if the pointer representation is smaller than the integer type, otherwise |
| the bits are unchanged. |
| <!-- ??? We've always claimed that pointers were unsigned entities. --> |
| <!-- Shouldn't we therefore be doing zero-extension? If so, the bug --> |
| <!-- is in convert_to_integer, where we call type_for_size and request --> |
| <!-- a signed integral type. On the other hand, it might be most useful --> |
| <!-- for the target if we extend according to POINTERS_EXTEND_UNSIGNED. --> |
| |
| <p>A cast from integer to pointer discards most-significant bits if the |
| pointer representation is smaller than the integer type, extends according |
| to the signedness of the integer type if the pointer representation |
| is larger than the integer type, otherwise the bits are unchanged. |
| |
| <p>When casting from pointer to integer and back again, the resulting |
| pointer must reference the same object as the original pointer, otherwise |
| the behavior is undefined. That is, one may not use integer arithmetic to |
| avoid the undefined behavior of pointer arithmetic as proscribed in |
| C99 6.5.6/8. |
| |
| <li><cite>The size of the result of subtracting two pointers to elements |
| of the same array (C90 6.3.6, C99 6.5.6).</cite> |
| |
| <p>The value is as specified in the standard and the type is determined |
| by the ABI. |
| |
| </ul> |
| |
| <div class="footnote"> |
| <hr> |
| <h4>Footnotes</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> Future versions of GCC may zero-extend, or use |
| a target-defined <code>ptr_extend</code> pattern. Do not rely on sign extension.</p> |
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