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| <a name="s390-Operands"></a> |
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| Next: <a href="s390-Formats.html#s390-Formats" accesskey="n" rel="next">s390 Formats</a>, Previous: <a href="s390-Mnemonics.html#s390-Mnemonics" accesskey="p" rel="prev">s390 Mnemonics</a>, Up: <a href="s390-Syntax.html#s390-Syntax" accesskey="u" rel="up">s390 Syntax</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Instruction-Operands"></a> |
| <h4 class="subsubsection">9.38.3.3 Instruction Operands</h4> |
| <a name="index-instruction-operands_002c-s390"></a> |
| <a name="index-s390-instruction-operands"></a> |
| |
| <p>Instruction operands can be grouped into three classes, operands located |
| in registers, immediate operands, and operands in storage. |
| </p> |
| <p>A register operand can be located in general, floating-point, access, |
| or control register. The register is identified by a four-bit field. |
| The field containing the register operand is called the R field. |
| </p> |
| <p>Immediate operands are contained within the instruction and can have |
| 8, 16 or 32 bits. The field containing the immediate operand is called |
| the I field. Dependent on the instruction the I field is either signed |
| or unsigned. |
| </p> |
| <p>A storage operand consists of an address and a length. The address of a |
| storage operands can be specified in any of these ways: |
| </p> |
| <ul> |
| <li> The content of a single general R |
| </li><li> The sum of the content of a general register called the base |
| register B plus the content of a displacement field D |
| </li><li> The sum of the contents of two general registers called the |
| index register X and the base register B plus the content of a |
| displacement field |
| </li><li> The sum of the current instruction address and a 32-bit signed |
| immediate field multiplied by two. |
| </li></ul> |
| |
| <p>The length of a storage operand can be: |
| </p> |
| <ul> |
| <li> Implied by the instruction |
| </li><li> Specified by a bitmask |
| </li><li> Specified by a four-bit or eight-bit length field L |
| </li><li> Specified by the content of a general register |
| </li></ul> |
| |
| <p>The notation for storage operand addresses formed from multiple fields is |
| as follows: |
| </p> |
| <dl compact="compact"> |
| <dt><code>Dn(Bn)</code></dt> |
| <dd><p>the address for operand number n is formed from the content of general |
| register Bn called the base register and the displacement field Dn. |
| </p></dd> |
| <dt><code>Dn(Xn,Bn)</code></dt> |
| <dd><p>the address for operand number n is formed from the content of general |
| register Xn called the index register, general register Bn called the |
| base register and the displacement field Dn. |
| </p></dd> |
| <dt><code>Dn(Ln,Bn)</code></dt> |
| <dd><p>the address for operand number n is formed from the content of general |
| regiser Bn called the base register and the displacement field Dn. |
| The length of the operand n is specified by the field Ln. |
| </p></dd> |
| </dl> |
| |
| <p>The base registers Bn and the index registers Xn of a storage operand can |
| be skipped. If Bn and Xn are skipped, a zero will be stored to the operand |
| field. The notation changes as follows: |
| </p> |
| <div class="display"> |
| <table> |
| <thead><tr><th width="30%"><pre class="display">full notation</pre></th><th width="30%"><pre class="display">short notation</pre></th></tr></thead> |
| <tr><td width="30%"><pre class="display">Dn(0,Bn)</pre></td><td width="30%"><pre class="display">Dn(Bn)</pre></td></tr> |
| <tr><td width="30%"><pre class="display">Dn(0,0)</pre></td><td width="30%"><pre class="display">Dn</pre></td></tr> |
| <tr><td width="30%"><pre class="display">Dn(0)</pre></td><td width="30%"><pre class="display">Dn</pre></td></tr> |
| <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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