| The Android Open Source Project | f6c3871 | 2009-03-03 19:28:47 -0800 | [diff] [blame^] | 1 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> |
| 2 | |
| 3 | <html> |
| 4 | |
| 5 | <head> |
| 6 | <title>if-test</title> |
| 7 | <link rel=stylesheet href="opcode.css"> |
| 8 | </head> |
| 9 | |
| 10 | <body> |
| 11 | |
| 12 | <h1>if-test</h1> |
| 13 | |
| 14 | <h2>Purpose</h2> |
| 15 | |
| 16 | <p> |
| 17 | Branch to the given destination if the given two registers' values compare as |
| 18 | specified. |
| 19 | </p> |
| 20 | <p> |
| 21 | Note: The branch offset may not be 0. (A spin loop may be legally constructed |
| 22 | either by branching around a backward goto or by including a nop as a target |
| 23 | before the branch.) |
| 24 | </p> |
| 25 | |
| 26 | <h2>Details</h2> |
| 27 | |
| 28 | <table class="instruc"> |
| 29 | <thead> |
| 30 | <tr> |
| 31 | <th>Op & Format</th> |
| 32 | <th>Mnemonic / Syntax</th> |
| 33 | <th>Arguments</th> |
| 34 | </tr> |
| 35 | </thead> |
| 36 | <tbody> |
| 37 | <tr> |
| 38 | <td>32..37 22t</td> |
| 39 | <td>if-<i>test</i> vA, vB, +CCCC<br/> |
| 40 | 32: if-eq<br/> |
| 41 | 33: if-ne<br/> |
| 42 | 34: if-lt<br/> |
| 43 | 35: if-ge<br/> |
| 44 | 36: if-gt<br/> |
| 45 | 37: if-le<br/> |
| 46 | </td> |
| 47 | <td><code>A:</code> first register to test (4 bits)<br/> |
| 48 | <code>B:</code> second register to test (4 bits)<br/> |
| 49 | <code>C:</code> signed branch offset (16 bits)</td> |
| 50 | </tr> |
| 51 | </tbody> |
| 52 | </table> |
| 53 | |
| 54 | <h2>Constraints</h2> |
| 55 | |
| 56 | <ul> |
| 57 | <li> |
| 58 | A and B must be valid register indices for the current stack frame. |
| 59 | </li> |
| 60 | <li> |
| 61 | Registers vA and vB must not contain a reference value. |
| 62 | </li> |
| 63 | <li> |
| 64 | Registers vA and vB must not be part of a register pair. |
| 65 | </li> |
| 66 | <li> |
| 67 | Registers vA and vB must not contain a floating point value (???). |
| 68 | </li> |
| 69 | C must of a signed offset that, when added to the PC of the instruction, |
| 70 | points to a valid bytecode instruction inside the same method. |
| 71 | </li> |
| 72 | </ul> |
| 73 | |
| 74 | <h2>Behavior</h2> |
| 75 | |
| 76 | <ul> |
| 77 | <li> |
| 78 | The values of registers vA and vB are compared according to the <test> |
| 79 | condition. Two results are possible: |
| 80 | <ul> |
| 81 | <li> |
| 82 | The condition holds. The value of C is used as a signed offset to the |
| 83 | address of the if-<test> instruction. Execution continues at the |
| 84 | resulting address. |
| 85 | </li> |
| 86 | <li> |
| 87 | The condition does not hold. Execution continues at the instruction |
| 88 | following the if-<test> instruction. |
| 89 | </li> |
| 90 | </ul> |
| 91 | </li> |
| 92 | </ul> |
| 93 | |
| 94 | <h2>Exceptions</h2> |
| 95 | |
| 96 | <p> |
| 97 | None. |
| 98 | </p> |
| 99 | |
| 100 | </body> |
| 101 | </html> |