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>array-length</title> 7 <link rel=stylesheet href="opcode.css"> 8 </head> 9 10 <body> 11 12 <h1>array-length</h1> 13 14 <h2>Purpose</h2> 15 16 <p> 17 Store in the given destination register the length of the indicated array, 18 in entries. 19 </p> 20 21 <h2>Details</h2> 22 23 <table class="instruc"> 24 <thead> 25 <tr> 26 <th>Op & Format</th> 27 <th>Mnemonic / Syntax</th> 28 <th>Arguments</th> 29 </tr> 30 </thead> 31 <tbody> 32 <tr> 33 <td>21 12x</td> 34 <td>array-length vA, vB</td> 35 <td><code>A:</code> destination register (4 bits)<br/> 36 <code>B:</code> array reference-bearing register (4 bits)</td> 37 </tr> 38 </tbody> 39 </table> 40 41 <h2>Constraints</h2> 42 43 <ul> 44 <li> 45 Both A and B must be valid register indices for the current stack frame. 46 </li> 47 <li> 48 Register vB must contain a reference to an array. 49 </li> 50 </ul> 51 52 <h2>Behavior</h2> 53 54 <ul> 55 <li> 56 The length of the array referenced by vB is stored in vA, that is 57 vA' = length(vB). 58 </li> 59 <li> 60 If register v(A-1) is the lower half of a register pair, register v(A-1)' 61 becomes undefined. 62 </li> 63 <li> 64 If register v(A+1) is the upper half of a register pair, register v(A+1)' 65 becomes undefined. 66 </li> 67 </ul> 68 69 <h2>Exceptions</h2> 70 71 <ul> 72 <li> 73 NullPointerException is thrown if the value of register vB is null. 74 </li> 75 </ul> 76 77 </body> 78 </html> 79
