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| <h5 class="subsubsection">9.41.3.3 Instruction Operands</h5> |
| |
| <p><a name="index-instruction-operands_002c-s390-2072"></a><a name="index-s390-instruction-operands-2073"></a> |
| Instruction operands can be grouped into three classes, operands located |
| in registers, immediate operands, and operands in storage. |
| |
| <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>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>A storage operand consists of an address and a length. The address of a |
| storage operands can be specified in any of these ways: |
| |
| <ul> |
| <li>The content of a single general R |
| <li>The sum of the content of a general register called the base |
| register B plus the content of a displacement field D |
| <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>The sum of the current instruction address and a 32-bit signed |
| immediate field multiplied by two. |
| </ul> |
| |
| <p>The length of a storage operand can be: |
| |
| <ul> |
| <li>Implied by the instruction |
| <li>Specified by a bitmask |
| <li>Specified by a four-bit or eight-bit length field L |
| <li>Specified by the content of a general register |
| </ul> |
| |
| <p>The notation for storage operand addresses formed from multiple fields is |
| as follows: |
| |
| <dl> |
| <dt><code>Dn(Bn)</code><dd>the address for operand number n is formed from the content of general |
| register Bn called the base register and the displacement field Dn. |
| <br><dt><code>Dn(Xn,Bn)</code><dd>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. |
| <br><dt><code>Dn(Ln,Bn)</code><dd>the address for operand number n is formed from the content of general |
| register Bn called the base register and the displacement field Dn. |
| The length of the operand n is specified by the field Ln. |
| </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: |
| |
| <pre class="display"> |
| <p><table summary=""><tr align="left"><th valign="top" width="30%">full notation </th><th valign="top" width="30%">short notation |
| <br></th></tr><tr align="left"><td valign="top" width="30%">Dn(0,Bn) </td><td valign="top" width="30%">Dn(Bn) |
| <br></td></tr><tr align="left"><td valign="top" width="30%">Dn(0,0) </td><td valign="top" width="30%">Dn |
| <br></td></tr><tr align="left"><td valign="top" width="30%">Dn(0) </td><td valign="top" width="30%">Dn |
| <br></td></tr><tr align="left"><td valign="top" width="30%">Dn(Ln,0) </td><td valign="top" width="30%">Dn(Ln) |
| <br></td></tr></table> |
| </pre> |
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