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114 lines
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<title>s390 Operands - Using as</title>
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="s390-Syntax.html#s390-Syntax" title="s390 Syntax">
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<link rel="prev" href="s390-Mnemonics.html#s390-Mnemonics" title="s390 Mnemonics">
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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</head>
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<body>
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<div class="node">
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<a name="s390-Operands"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="s390-Formats.html#s390-Formats">s390 Formats</a>,
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Previous: <a rel="previous" accesskey="p" href="s390-Mnemonics.html#s390-Mnemonics">s390 Mnemonics</a>,
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Up: <a rel="up" accesskey="u" href="s390-Syntax.html#s390-Syntax">s390 Syntax</a>
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<hr>
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</div>
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<h5 class="subsubsection">9.41.3.3 Instruction Operands</h5>
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<p><a name="index-instruction-operands_002c-s390-2072"></a><a name="index-s390-instruction-operands-2073"></a>
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Instruction operands can be grouped into three classes, operands located
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in registers, immediate operands, and operands in storage.
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<p>A register operand can be located in general, floating-point, access,
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or control register. The register is identified by a four-bit field.
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The field containing the register operand is called the R field.
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<p>Immediate operands are contained within the instruction and can have
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8, 16 or 32 bits. The field containing the immediate operand is called
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the I field. Dependent on the instruction the I field is either signed
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or unsigned.
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<p>A storage operand consists of an address and a length. The address of a
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storage operands can be specified in any of these ways:
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<ul>
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<li>The content of a single general R
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<li>The sum of the content of a general register called the base
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register B plus the content of a displacement field D
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<li>The sum of the contents of two general registers called the
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index register X and the base register B plus the content of a
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displacement field
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<li>The sum of the current instruction address and a 32-bit signed
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immediate field multiplied by two.
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</ul>
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<p>The length of a storage operand can be:
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<ul>
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<li>Implied by the instruction
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<li>Specified by a bitmask
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<li>Specified by a four-bit or eight-bit length field L
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<li>Specified by the content of a general register
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</ul>
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<p>The notation for storage operand addresses formed from multiple fields is
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as follows:
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<dl>
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<dt><code>Dn(Bn)</code><dd>the address for operand number n is formed from the content of general
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register Bn called the base register and the displacement field Dn.
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<br><dt><code>Dn(Xn,Bn)</code><dd>the address for operand number n is formed from the content of general
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register Xn called the index register, general register Bn called the
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base register and the displacement field Dn.
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<br><dt><code>Dn(Ln,Bn)</code><dd>the address for operand number n is formed from the content of general
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register Bn called the base register and the displacement field Dn.
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The length of the operand n is specified by the field Ln.
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</dl>
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<p>The base registers Bn and the index registers Xn of a storage operand can
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be skipped. If Bn and Xn are skipped, a zero will be stored to the operand
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field. The notation changes as follows:
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<pre class="display">
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<p><table summary=""><tr align="left"><th valign="top" width="30%">full notation </th><th valign="top" width="30%">short notation
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<br></th></tr><tr align="left"><td valign="top" width="30%">Dn(0,Bn) </td><td valign="top" width="30%">Dn(Bn)
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<br></td></tr><tr align="left"><td valign="top" width="30%">Dn(0,0) </td><td valign="top" width="30%">Dn
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<br></td></tr><tr align="left"><td valign="top" width="30%">Dn(0) </td><td valign="top" width="30%">Dn
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<br></td></tr><tr align="left"><td valign="top" width="30%">Dn(Ln,0) </td><td valign="top" width="30%">Dn(Ln)
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<br></td></tr></table>
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</pre>
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</body></html>
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