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Primitive-types.html

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  3. <title>Primitive types - avram - a virtual machine code interpreter</title>
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  27. <a name="Primitive-types"></a>
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  28. <p>
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  29. Next:&nbsp;<a rel="next" accesskey="n" href="One-dimensional-arrays.html#One-dimensional-arrays">One dimensional arrays</a>,
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  30. Previous:&nbsp;<a rel="previous" accesskey="p" href="Type-Conversions.html#Type-Conversions">Type Conversions</a>,
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  31. Up:&nbsp;<a rel="up" accesskey="u" href="Type-Conversions.html#Type-Conversions">Type Conversions</a>
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  32. <hr>
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  33. </div>
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  34. 

  35. <h5 class="subsubsection">3.1.4.1 Primitive types</h5>
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  36. 

  37. <p>A pair of functions in support of this abstraction is prototyped in
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  38. <samp><span class="file">listfuns.h</span></samp>.  These functions will be of interest mainly to
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  39. developers wishing to implement an interface to a new library module
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  40. and make it accessible on the virtual side by way of the
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  41. <code>library</code> combinator (<a href="Library-combinator.html#Library-combinator">Library combinator</a>).
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  42. 

  43. <div class="defun">
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  44. &mdash; Function: void <b>*avm_value_of_list</b> (<var>list operand, list *message, int *fault</var>)<var><a name="index-g_t_002aavm_005fvalue_005fof_005flist-440"></a></var><br>
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  45. <blockquote><p>This function takes an <var>operand</var> representing a value used by a
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  46. library function in the format described above (<a href="Type-Conversions.html#Type-Conversions">Type Conversions</a>) and returns a pointer to the value.
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  47. 

  48.         <p>The <code>value</code> field in the <var>operand</var> normally will point to the
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  49. block of memory holding the value, and the <var>operand</var> itself will
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  50. be a list of character representations whose binary encodings spell
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  51. out the value as explained above.
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  52. 

  53.         <p>The <code>value</code> field need not be initialized on entry but it will be
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  54. initialized as a side effect of being computed by this function. If it
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  55. has been initialized due to a previous call with the same
    56. 

  56. <var>operand</var>, this function is a fast constant time operation.
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  57. 

  58.         <p>The caller should not free the pointer returned by this function
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  59. because a reference to its value will remain in the
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  60. <var>operand</var>. When the <var>operand</var> itself is freed by
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  61. <code>avm_dispose</code> (<a href="Simple-Operations.html#Simple-Operations">Simple Operations</a>), the value will go with it.
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  62. 

  63.         <p>If an error occurs during the evaluation of this function, the integer
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  64. referenced by <var>fault</var> will be set to a non-zero value, and the
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  65. list referenced by <var>message</var> will be assigned a representation of
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  66. a list of strings describing the error. The <var>message</var> is freshly
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  67. created and should be freed by the caller with <code>avm_dispose</code>
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  68. when no longer needed.
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  69. 

  70.         <p>Possible error messages are <code>&lt;'missing value'&gt;</code>, in the case of
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  71. <a name="index-missing-value-441"></a>an empty <var>operand</var>, <code>&lt;'invalid value'&gt;</code> in the case of an
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  72. <a name="index-invalid-value-442"></a><var>operand</var> that is not a list of character representations, and
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  73. <code>&lt;'memory overflow'&gt;</code> if there was insufficient space to allocate
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  74. the result. 
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  75. </p></blockquote></div>
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  76. 

  77. <div class="defun">
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  78. &mdash; Function: list <b>avm_list_of_value</b> (<var>void *contents, size_t size, int *fault</var>)<var><a name="index-avm_005flist_005fof_005fvalue-443"></a></var><br>
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  79. <blockquote><p>This function performs the inverse operation of
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  80. <code>avm_value_of_list</code>, taking the address of an area of
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  81. contiguously stored data and its <var>size</var> in bytes to a list
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  82. representation. The length of the list returned is equal to the number
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  83. of bytes of data, <var>size</var>, and each item of the list is a character
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  84. representation for the corresponding byte as given by <a href="Character-Table.html#Character-Table">Character Table</a>.
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  85. 

  86.         <p>A copy of the memory area is made so that the original is no longer
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  87. needed and may be freed by the caller. A pointer to this copy is
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  88. returned by subsequent calls to <code>avm_value_of_list</code> when the
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  89. result returned by this function is used as the <var>operand</var>
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  90. parameter.
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  91. 

  92.         <p>If there is insufficient memory to allocate the result, the integer
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  93. referenced by <var>fault</var> is set to a non-zero value, and a copy of
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  94. the message <code>&lt;'memory overflow'&gt;</code> represented as a list is
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  95. returned. This function could also cause a segmentation fault if it is
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  96. <a name="index-segmentation-fault-444"></a>passed an invalid pointer or a <var>size</var> that overruns the storage
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  97. area.  However, it is acceptable to specify a <var>size</var> that is less
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  98. than the actual size of the given memory area to construct a list
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  99. representing only the first part of it. The <var>size</var> must always be
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  100. greater than zero. 
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  101. </p></blockquote></div>
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