| <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> |
| |
| <html> |
| |
| <head> |
| <title>if-test</title> |
| <link rel=stylesheet href="opcode.css"> |
| </head> |
| |
| <body> |
| |
| <h1>if-test</h1> |
| |
| <h2>Purpose</h2> |
| |
| <p> |
| Branch to the given destination if the given two registers' values compare as |
| specified. |
| </p> |
| <p> |
| Note: The branch offset may not be 0. (A spin loop may be legally constructed |
| either by branching around a backward goto or by including a nop as a target |
| before the branch.) |
| </p> |
| |
| <h2>Details</h2> |
| |
| <table class="instruc"> |
| <thead> |
| <tr> |
| <th>Op & Format</th> |
| <th>Mnemonic / Syntax</th> |
| <th>Arguments</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td>32..37 22t</td> |
| <td>if-<i>test</i> vA, vB, +CCCC<br/> |
| 32: if-eq<br/> |
| 33: if-ne<br/> |
| 34: if-lt<br/> |
| 35: if-ge<br/> |
| 36: if-gt<br/> |
| 37: if-le<br/> |
| </td> |
| <td><code>A:</code> first register to test (4 bits)<br/> |
| <code>B:</code> second register to test (4 bits)<br/> |
| <code>C:</code> signed branch offset (16 bits)</td> |
| </tr> |
| </tbody> |
| </table> |
| |
| <h2>Constraints</h2> |
| |
| <ul> |
| <li> |
| A and B must be valid register indices for the current stack frame. |
| </li> |
| <li> |
| Registers vA and vB must not contain a reference value. |
| </li> |
| <li> |
| Registers vA and vB must not be part of a register pair. |
| </li> |
| <li> |
| Registers vA and vB must not contain a floating point value (???). |
| </li> |
| C must of a signed offset that, when added to the PC of the instruction, |
| points to a valid bytecode instruction inside the same method. |
| </li> |
| </ul> |
| |
| <h2>Behavior</h2> |
| |
| <ul> |
| <li> |
| The values of registers vA and vB are compared according to the <test> |
| condition. Two results are possible: |
| <ul> |
| <li> |
| The condition holds. The value of C is used as a signed offset to the |
| address of the if-<test> instruction. Execution continues at the |
| resulting address. |
| </li> |
| <li> |
| The condition does not hold. Execution continues at the instruction |
| following the if-<test> instruction. |
| </li> |
| </ul> |
| </li> |
| </ul> |
| |
| <h2>Exceptions</h2> |
| |
| <p> |
| None. |
| </p> |
| |
| </body> |
| </html> |
