s390-Operands.html 6.7 KB

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  63. <a name="Instruction-Operands"></a>
  64. <h4 class="subsubsection">9.39.3.3 Instruction Operands</h4>
  65. <a name="index-instruction-operands_002c-s390"></a>
  66. <a name="index-s390-instruction-operands"></a>
  67. <p>Instruction operands can be grouped into three classes, operands located
  68. in registers, immediate operands, and operands in storage.
  69. </p>
  70. <p>A register operand can be located in general, floating-point, access,
  71. or control register. The register is identified by a four-bit field.
  72. The field containing the register operand is called the R field.
  73. </p>
  74. <p>Immediate operands are contained within the instruction and can have
  75. 8, 16 or 32 bits. The field containing the immediate operand is called
  76. the I field. Dependent on the instruction the I field is either signed
  77. or unsigned.
  78. </p>
  79. <p>A storage operand consists of an address and a length. The address of a
  80. storage operands can be specified in any of these ways:
  81. </p>
  82. <ul>
  83. <li> The content of a single general R
  84. </li><li> The sum of the content of a general register called the base
  85. register B plus the content of a displacement field D
  86. </li><li> The sum of the contents of two general registers called the
  87. index register X and the base register B plus the content of a
  88. displacement field
  89. </li><li> The sum of the current instruction address and a 32-bit signed
  90. immediate field multiplied by two.
  91. </li></ul>
  92. <p>The length of a storage operand can be:
  93. </p>
  94. <ul>
  95. <li> Implied by the instruction
  96. </li><li> Specified by a bitmask
  97. </li><li> Specified by a four-bit or eight-bit length field L
  98. </li><li> Specified by the content of a general register
  99. </li></ul>
  100. <p>The notation for storage operand addresses formed from multiple fields is
  101. as follows:
  102. </p>
  103. <dl compact="compact">
  104. <dt><code>Dn(Bn)</code></dt>
  105. <dd><p>the address for operand number n is formed from the content of general
  106. register Bn called the base register and the displacement field Dn.
  107. </p></dd>
  108. <dt><code>Dn(Xn,Bn)</code></dt>
  109. <dd><p>the address for operand number n is formed from the content of general
  110. register Xn called the index register, general register Bn called the
  111. base register and the displacement field Dn.
  112. </p></dd>
  113. <dt><code>Dn(Ln,Bn)</code></dt>
  114. <dd><p>the address for operand number n is formed from the content of general
  115. regiser Bn called the base register and the displacement field Dn.
  116. The length of the operand n is specified by the field Ln.
  117. </p></dd>
  118. </dl>
  119. <p>The base registers Bn and the index registers Xn of a storage operand can
  120. be skipped. If Bn and Xn are skipped, a zero will be stored to the operand
  121. field. The notation changes as follows:
  122. </p>
  123. <div class="display">
  124. <table>
  125. <thead><tr><th width="30%"><pre class="display">full notation</pre></th><th width="30%"><pre class="display">short notation</pre></th></tr></thead>
  126. <tr><td width="30%"><pre class="display">Dn(0,Bn)</pre></td><td width="30%"><pre class="display">Dn(Bn)</pre></td></tr>
  127. <tr><td width="30%"><pre class="display">Dn(0,0)</pre></td><td width="30%"><pre class="display">Dn</pre></td></tr>
  128. <tr><td width="30%"><pre class="display">Dn(0)</pre></td><td width="30%"><pre class="display">Dn</pre></td></tr>
  129. <tr><td width="30%"><pre class="display">Dn(Ln,0)</pre></td><td width="30%"><pre class="display">Dn(Ln)</pre></td></tr>
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