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| <a name="Constant-expressions"></a> |
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| Next: <a href="Storage-References.html#Storage-References" accesskey="n" rel="next">Storage References</a>, Up: <a href="Expression-trees.html#Expression-trees" accesskey="u" rel="up">Expression trees</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Constant-expressions-1"></a> |
| <h4 class="subsection">10.6.1 Constant expressions</h4> |
| <a name="index-INTEGER_005fCST"></a> |
| <a name="index-TREE_005fINT_005fCST_005fHIGH"></a> |
| <a name="index-TREE_005fINT_005fCST_005fLOW"></a> |
| <a name="index-tree_005fint_005fcst_005flt"></a> |
| <a name="index-tree_005fint_005fcst_005fequal"></a> |
| <a name="index-REAL_005fCST"></a> |
| <a name="index-FIXED_005fCST"></a> |
| <a name="index-COMPLEX_005fCST"></a> |
| <a name="index-VECTOR_005fCST"></a> |
| <a name="index-STRING_005fCST"></a> |
| <a name="index-TREE_005fSTRING_005fLENGTH"></a> |
| <a name="index-TREE_005fSTRING_005fPOINTER"></a> |
| |
| <p>The table below begins with constants, moves on to unary expressions, |
| then proceeds to binary expressions, and concludes with various other |
| kinds of expressions: |
| </p> |
| <dl compact="compact"> |
| <dt><code>INTEGER_CST</code></dt> |
| <dd><p>These nodes represent integer constants. Note that the type of these |
| constants is obtained with <code>TREE_TYPE</code>; they are not always of type |
| <code>int</code>. In particular, <code>char</code> constants are represented with |
| <code>INTEGER_CST</code> nodes. The value of the integer constant <code>e</code> is |
| given by |
| </p><div class="smallexample"> |
| <pre class="smallexample">((TREE_INT_CST_HIGH (e) << HOST_BITS_PER_WIDE_INT) |
| + TREE_INST_CST_LOW (e)) |
| </pre></div> |
| <p>HOST_BITS_PER_WIDE_INT is at least thirty-two on all platforms. Both |
| <code>TREE_INT_CST_HIGH</code> and <code>TREE_INT_CST_LOW</code> return a |
| <code>HOST_WIDE_INT</code>. The value of an <code>INTEGER_CST</code> is interpreted |
| as a signed or unsigned quantity depending on the type of the constant. |
| In general, the expression given above will overflow, so it should not |
| be used to calculate the value of the constant. |
| </p> |
| <p>The variable <code>integer_zero_node</code> is an integer constant with value |
| zero. Similarly, <code>integer_one_node</code> is an integer constant with |
| value one. The <code>size_zero_node</code> and <code>size_one_node</code> variables |
| are analogous, but have type <code>size_t</code> rather than <code>int</code>. |
| </p> |
| <p>The function <code>tree_int_cst_lt</code> is a predicate which holds if its |
| first argument is less than its second. Both constants are assumed to |
| have the same signedness (i.e., either both should be signed or both |
| should be unsigned.) The full width of the constant is used when doing |
| the comparison; the usual rules about promotions and conversions are |
| ignored. Similarly, <code>tree_int_cst_equal</code> holds if the two |
| constants are equal. The <code>tree_int_cst_sgn</code> function returns the |
| sign of a constant. The value is <code>1</code>, <code>0</code>, or <code>-1</code> |
| according on whether the constant is greater than, equal to, or less |
| than zero. Again, the signedness of the constant’s type is taken into |
| account; an unsigned constant is never less than zero, no matter what |
| its bit-pattern. |
| </p> |
| </dd> |
| <dt><code>REAL_CST</code></dt> |
| <dd> |
| <p>FIXME: Talk about how to obtain representations of this constant, do |
| comparisons, and so forth. |
| </p> |
| </dd> |
| <dt><code>FIXED_CST</code></dt> |
| <dd> |
| <p>These nodes represent fixed-point constants. The type of these constants |
| is obtained with <code>TREE_TYPE</code>. <code>TREE_FIXED_CST_PTR</code> points to |
| a <code>struct fixed_value</code>; <code>TREE_FIXED_CST</code> returns the structure |
| itself. <code>struct fixed_value</code> contains <code>data</code> with the size of two |
| <code>HOST_BITS_PER_WIDE_INT</code> and <code>mode</code> as the associated fixed-point |
| machine mode for <code>data</code>. |
| </p> |
| </dd> |
| <dt><code>COMPLEX_CST</code></dt> |
| <dd><p>These nodes are used to represent complex number constants, that is a |
| <code>__complex__</code> whose parts are constant nodes. The |
| <code>TREE_REALPART</code> and <code>TREE_IMAGPART</code> return the real and the |
| imaginary parts respectively. |
| </p> |
| </dd> |
| <dt><code>VECTOR_CST</code></dt> |
| <dd><p>These nodes are used to represent vector constants, whose parts are |
| constant nodes. Each individual constant node is either an integer or a |
| double constant node. The first operand is a <code>TREE_LIST</code> of the |
| constant nodes and is accessed through <code>TREE_VECTOR_CST_ELTS</code>. |
| </p> |
| </dd> |
| <dt><code>STRING_CST</code></dt> |
| <dd><p>These nodes represent string-constants. The <code>TREE_STRING_LENGTH</code> |
| returns the length of the string, as an <code>int</code>. The |
| <code>TREE_STRING_POINTER</code> is a <code>char*</code> containing the string |
| itself. The string may not be <code>NUL</code>-terminated, and it may contain |
| embedded <code>NUL</code> characters. Therefore, the |
| <code>TREE_STRING_LENGTH</code> includes the trailing <code>NUL</code> if it is |
| present. |
| </p> |
| <p>For wide string constants, the <code>TREE_STRING_LENGTH</code> is the number |
| of bytes in the string, and the <code>TREE_STRING_POINTER</code> |
| points to an array of the bytes of the string, as represented on the |
| target system (that is, as integers in the target endianness). Wide and |
| non-wide string constants are distinguished only by the <code>TREE_TYPE</code> |
| of the <code>STRING_CST</code>. |
| </p> |
| <p>FIXME: The formats of string constants are not well-defined when the |
| target system bytes are not the same width as host system bytes. |
| </p> |
| </dd> |
| </dl> |
| |
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