turing_tarpit.html

   1 <html>
   2 <title>Turing Tarpit Simulator</title>
   3 <script>
   4
   5 /* internal values for simulated computer */
   6 var ins_pointer = 0;                    /* instruction pointer */
   7 var dat_pointer = 0;                    /* data pointer */
   8 var dat_pointer_changed = 0;            /* bool set to 1 if data pointer has changed in the last step */
   9 var dat_pointer_last_address = 0;       /* address of data pointer in last step */
  10 var ram_last_address = 0;               /* address of RAM updated in last step */
  11 var breakpoints = 1;                    /* bool set to 0 to ignore breakpoints */
  12 var ram = new Array();                  /* memory of virtual machine */
  13 var jmp = new Array();                  /* used as a stack to jump from one command to another */
  14 var ins = null;                         /* current instruction from code */
  15 var halt = false;                       /* halts program ASAP */
  16
  17 /* objects that display data to the user */
  18 var disp_docs;
  19 var disp_code;
  20 var disp_ram;
  21 var disp_ins_pointer;
  22 var disp_dat_pointer;
  23 var disp_pointer = "<div id=disp_pointer>&#8658;</div>"; /* data pointer displayed in memory block */
  24
  25 /* highlight current instruction running on machine */
  26 function code_highlight(inputEl, selStart, selEnd) {
  27         if (inputEl.setSelectionRange) {
  28                 inputEl.focus();
  29                 inputEl.setSelectionRange(selStart, selEnd);
  30         } else if (inputEl.createTextRange) {
  31                 var range = inputEl.createTextRange();
  32                 range.collapse(true);
  33                 range.moveEnd('character', selEnd);
  34                 range.moveStart('character', selStart);
  35                 range.select();
  36         }
  37 }
  38
  39 /* turns breakpoints on and off */
  40 function debug_toggle_breakpoints()
  41 {
  42         var button = document.getElementById("dbg_status");
  43         if(breakpoints) {
  44                 breakpoints=0;
  45                 button.innerHTML='<img src="http://opentextbook.info/icons/32x32/bug_delete.png">';
  46         }else {
  47                 breakpoints=1;
  48                 button.innerHTML='<img src="http://opentextbook.info/icons/32x32/bug_add.png">';
  49         }
  50 }
  51
  52 /* removes all breakpoints in source code */
  53 function debug_remove_breakpoints()
  54 {
  55         /* ask user for permission first */
  56         var ans = confirm("Permanently remove all breakpoints from code?");
  57         var code = document.getElementById("code");
  58         if(ans) { code.value = code.value.replace( /\*/g , '' ); }
  59 }
  60
  61 /* test current code character - return true if it is an instruction */
  62 /* tried to use regex on this and could not get it to work :( */
  63 function tst_inst()
  64 {
  65         if(ins == '+' ||  ins == '-' ||  ins == '>' ||  ins == '<' ||
  66           ins == '*' ||  ins == '.' ||  ins == '[' ||  ins == ']' ||  ins == ',') {
  67                 return true;
  68         }
  69         return false;
  70 }
  71
  72 /* find next instruction in code and move instruction pointer to it */
  73 function fnd_nxt_inst()
  74 {
  75         do {
  76                 if(ins_pointer > disp_code.value.length) { break; } /* must stop at end of code */
  77                 update_ins_pointer(1);
  78                 ins = disp_code.value.substring(ins_pointer-1,ins_pointer); /* get data at ins_pointer location */
  79         }while(!tst_inst());
  80         if(ins_pointer > disp_code.value.length) {
  81                 alert("HALT: Program is Complete");
  82                 halt = true;
  83                 reset();
  84         }
  85
  86         /* highlight code currently executing on screen */
  87         code_highlight(disp_code, ins_pointer-1, ins_pointer);
  88 }
  89
  90 /* find previous instruction in code and move instruction pointer to it */
  91 function fnd_prv_inst()
  92 {
  93         ins_pointer--;
  94         while(ins_pointer >= 0)
  95         {
  96                 ins = disp_code.value.substring(ins_pointer-1, ins_pointer); /* get data at ins_pointer location */
  97                 if(tst_inst()) { return; }
  98                 ins_pointer--;
  99         }
 100         if(ins_pointer == 0) {
 101                 alert("SEGFAULT: Program could not find corresponding jump instruction");
 102                 halt = true;
 103                 reset();
 104         }
 105 }
 106
 107 /* execute next instruction from input */
 108 function exe_nxt_inst()
 109 {
 110         var temp_count = 0;
 111         fnd_nxt_inst();
 112         switch(ins)
 113         {
 114                 case '+':
 115                         ram_modify(dat_pointer, 1);
 116                         break;
 117                 case '-':
 118                         ram_modify(dat_pointer, -1);
 119                         break;
 120                 case '>':
 121                         dat_point_modify(1);
 122                         break;
 123                 case '<':
 124                         dat_point_modify(-1);
 125                         break;
 126                 case '*': /* these are comments - a break from the standard language */
 127                         if(breakpoints) { stop(); }
 128                         break;
 129                 case '.':
 130                         print_mem();
 131                         break;
 132                 case '[':
 133                         jump_fwd();
 134                         break;
 135                 case ']':
 136                         jump_bak();
 137                         break;
 138                 case ',':
 139                         break;
 140                 default:
 141                         /* must be a comment :) */
 142         }
 143 }
 144
 145 /* if byte at data pointer is = 0, jump forward to instruction after matching ']' command */
 146 function jump_fwd()
 147 {
 148         if(ram[dat_pointer] != 0) { return; }
 149         /* add this jump to stack */
 150         jmp.push('[');
 151         /* loop through code, pushing and popping stack until stack is empty */
 152         while(jmp.length > 0) {
 153                 fnd_nxt_inst();
 154                 if(ins == ']') { jmp.pop();
 155                 } else if (ins == '[') { jmp.push(']'); }
 156         }
 157 }
 158
 159 /* if byte at data pointer is != 0, jump back to instruction after matching '[' command */
 160 function jump_bak()
 161 {
 162         if(ram[dat_pointer] == 0) { return; }
 163         /* add this jump to stack */
 164         jmp.push(']');
 165         /* loop through code, pushing and popping stack until stack is empty */
 166         while(jmp.length > 0 && ins_pointer > 0) {
 167                 fnd_prv_inst();
 168                 if(ins == '[') { jmp.pop();
 169                 } else if (ins == ']') { jmp.push(']'); }
 170         }
 171 }
 172
 173 /*
 174         rewind code to beginning reset all memory locations
 175         this simulates rebooting the computer
 176 */
 177 function reset()
 178 {
 179         update_ins_pointer(0);
 180         dat_point_modify(0);
 181         ram_reset();
 182         ram_highlight_clear();
 183         dat_point_highlight();
 184         document.getElementById("output_disp").innerHTML = '';
 185         document.getElementById("addr_0").innerHTML = "0" + disp_pointer;
 186         dat_point_highlight_clear();
 187 }
 188
 189 /* stop stepping through code on timer if breakpoints enabled */
 190 function stop()
 191 {
 192         halt = true;
 193 }
 194
 195 /* run through program on timer, stopping at breakpoints if enabled */
 196 function run()
 197 {
 198         var total_steps = document.getElementById("code").value.length;
 199         while(ins_pointer <= total_steps && halt == false) { step_next(); }
 200 }
 201
 202 /* step forward one instruction */
 203 function step_next()
 204 {
 205         //update_ins_pointer(1);
 206         exe_nxt_inst();
 207         dat_point_highlight();
 208 }
 209
 210 /* more back one instruction - undoes work of previous instruction */
 211 function step_back()
 212 {
 213         update_ins_pointer(-1);
 214         dat_point_highlight();
 215 }
 216
 217 /* update instruction pointer
 218         direction:
 219
 220         1 increment pointer by one
 221         0 set pointer to 0
 222         -1 decrement pointer by one
 223 */
 224 function update_ins_pointer(direction)
 225 {
 226         if(direction < 0 && ins_pointer != 0 ) { ins_pointer--; }
 227         else if (direction == 0 ) { ins_pointer = 0; }
 228         else { ins_pointer++; }
 229         disp_ins_pointer.value =  ins_pointer;
 230 }
 231
 232 /* update instruction pointer and set to new value */
 233 function ins_point_modify_by_address(val)
 234 {
 235         /* instruction pointer can never be less than 0 */
 236         if(val < 0) {
 237                 alert("Instruction Pointer cannot be set less than Zero.");
 238                 disp_ins_pointer.value =  ins_pointer; /* reset val to previous */
 239                 return;
 240         }
 241         if(val > disp_code.value.length) {
 242                 alert("Instruction Pointer cannot be set beyond end of code.\n Current length of code: " + disp_code.value.length);
 243                 disp_ins_pointer.value =  ins_pointer; /* reset val to previous */
 244                 return;
 245         }
 246         ins_pointer = disp_ins_pointer.value;
 247 }
 248
 249 /* setup virtual machine - must be called on page load */
 250 function init_form()
 251 {
 252         disp_code  = document.getElementById("code");
 253         disp_ins_pointer = document.getElementById("ins_pointer_disp");
 254         disp_dat_pointer = document.getElementById("dat_pointer_disp");
 255         disp_ram = document.getElementById("ram_disp");
 256         ram_reset();
 257         ram_init();
 258         document.getElementById("addr_0").innerHTML = "0" + disp_pointer;
 259         disp_docs = document.getElementById("docs");
 260         /* reset_output(); */
 261 }
 262
 263 /* reset all RAM to 0 */
 264 function ram_reset()
 265 {
 266         var i;
 267         for(i=0; i < 64; i++) { ram[i] = 0; }
 268 }
 269
 270 /* update highlight of one memory address and release other highlight if needed */
 271 function ram_highlight(address)
 272 {
 273         var disp_last_address = document.getElementById("ram_"+ram_last_address);
 274         /* highlight background of current address */
 275         document.getElementById("ram_"+address).style.backgroundColor = "#ff0";
 276
 277         /* remove highlight from last address modified */
 278         if(ram_last_address != address){
 279                 if(ram_last_address%2==0) {
 280                         disp_last_address.style.backgroundColor = "#fff";
 281                 } else {
 282                         disp_last_address.style.backgroundColor = "#def";
 283                 }
 284         }
 285 }
 286
 287 /* remove highlight from all memory cells regardless of current status */
 288 function ram_highlight_clear()
 289 {
 290         var i;
 291         for(i=0; i < 64; i++)
 292         {
 293                 if(i%2==0) {
 294                         document.getElementById("ram_"+i).style.backgroundColor = "#fff";
 295                 } else {
 296                         document.getElementById("ram_"+i).style.backgroundColor = "#def";
 297                 }
 298                 document.getElementById("ram_"+i).innerHTML = ram[i];
 299         }
 300 }
 301
 302 /* define RAM on screen */
 303 function ram_init()
 304 {
 305         var i;
 306         var table = "<table id=memory_table>\n";
 307         for(i=0; i < 16; i++){
 308                 if(i%2==0) {
 309                         table += "\t<tr class=even>";
 310                 } else {
 311                         table += "\t<tr class=odd>";
 312                 }
 313                 table += "<td width='35' class=addr id=addr_"+i+">"+i+"</td><td width='35' class=ram id=ram_"+i+">"+ram[i]+"</td>";
 314                 table += "<td width='35' class=addr id=addr_"+(i+16)+">"+(i+16)+"</td><td class=ram id=ram_"+(i+16)+">"+ram[i+16]+"</td>\n";
 315                 table += "<td class=addr id=addr_"+(i+32)+">"+(i+32)+"</td><td width='35' class=ram id=ram_"+(i+32)+">"+ram[i+32]+"</td>\n";
 316                 table += "<td class=addr id=addr_"+(i+48)+">"+(i+48)+"</td><td width='35' class=ram id=ram_"+(i+48)+">"+ram[i+48]+"</td></tr>\n";
 317         }
 318         table +=  "</table>\n";
 319         disp_ram.innerHTML = table;
 320 }
 321
 322 /*
 323         modify the value at this address - reset RAM highlights for all addresses
 324         1 increment RAM by one
 325         0 set RAM to 0
 326         -1 decrement RAM by one
 327 */
 328 function ram_modify(address, change)
 329 {
 330         if(address < 0 || address > 63) {
 331                 alert("SEGFAULT: Cannot Modify Data Outside of Memory Range");
 332                 halt = true;
 333                 reset();
 334                 return;
 335         }
 336
 337         if (change > 0 ) {
 338                 ram[address]++;
 339         } else if(change < 0 ) {
 340                 ram[address]--;
 341         } else {
 342                 ram[address] = 0;
 343         }
 344         ram_highlight(address);
 345         document.getElementById("ram_"+address).innerHTML = ram[address];
 346         ram_last_address = address;
 347 }
 348
 349 /*
 350         modify state of data pointer
 351         1 increment data pointer by one
 352         0 set data pointer to 0
 353         -1 decrement data pointer by one
 354
 355 */
 356 function dat_point_modify(change)
 357 {
 358         dat_pointer_last_address = dat_pointer;
 359         if (change > 0 ) {
 360                 dat_pointer++;
 361         } else if(change < 0 ) {
 362                 /* could put SEGFAULT here, but C does not have a check for this, so neither will I ;) */
 363                 dat_pointer--;
 364         } else {
 365                 dat_pointer = 0;
 366         }
 367
 368         /* place '>' char next to memory address in table */
 369         if(dat_pointer >= 0 && dat_pointer < 64) {
 370                 document.getElementById("addr_"+dat_pointer).innerHTML = dat_pointer + disp_pointer;
 371         }
 372
 373         /* remove '>' char next to memory address in table */
 374         if(dat_pointer_last_address >= 0 && dat_pointer_last_address < 64) {
 375                 document.getElementById("addr_"+dat_pointer_last_address).innerHTML = dat_pointer_last_address;
 376         }
 377
 378         disp_dat_pointer.value = dat_pointer;
 379         dat_pointer_changed = 1;
 380 }
 381
 382 function dat_point_modify_by_address(val)
 383 {
 384         dat_pointer_last_address = dat_pointer;
 385         dat_pointer = disp_dat_pointer.value;
 386         /* place '>' char next to memory address in table */
 387         if(dat_pointer >= 0 && dat_pointer < 64) {
 388                 document.getElementById("addr_"+dat_pointer).innerHTML = dat_pointer + disp_pointer;
 389         }
 390
 391         /* remove '>' char next to memory address in table */
 392         if(dat_pointer_last_address >= 0 && dat_pointer_last_address < 64) {
 393                 document.getElementById("addr_"+dat_pointer_last_address).innerHTML = dat_pointer_last_address;
 394         }
 395         dat_pointer_changed = 1;
 396         dat_point_highlight();
 397 }
 398
 399 /* turns on and off data pointer highlight if it has changed this step */
 400 function dat_point_highlight()
 401 {
 402         if(dat_pointer_changed) {
 403                 disp_dat_pointer.style.backgroundColor = "#ff0";
 404                 dat_pointer_changed = 0;
 405         } else {
 406                 disp_dat_pointer.style.backgroundColor = "#fff";
 407         }
 408
 409         /* as a convenience to the user, set to red if pointer is out of memory range */
 410         if(dat_pointer < 0 || dat_pointer > 63) {
 411                 disp_dat_pointer.style.backgroundColor = "#f00";
 412         }
 413 }
 414
 415 /* remove highlight from data pointer */
 416 function dat_point_highlight_clear()
 417 {
 418         disp_dat_pointer.style.backgroundColor = "#fff";
 419 }
 420
 421 /* print ASCII representation of memory at data pointer */
 422 function print_mem()
 423 {
 424         var x = String.fromCharCode(ram[dat_pointer]);
 425         document.getElementById("output_disp").innerHTML += x;
 426 }
 427
 428 /* documentation stored inside invisible div. This shows its contents. */
 429 function display_docs()
 430 {
 431         disp_docs.style.visibility = "visible";
 432         docs_select("docs_main");
 433 }
 434
 435 /* hide documentation from user */
 436 function hide_docs()
 437 {
 438         disp_docs.style.visibility = "hidden";
 439 }
 440
 441 function docs_select(page)
 442 {
 443         if(page == "basic") {
 444                 document.getElementById("docs_content").innerHTML = document.getElementById("docs_basic").innerHTML;
 445         } else if(page == "features") {
 446                 document.getElementById("docs_content").innerHTML = document.getElementById("docs_features").innerHTML;
 447         } else if(page == "examples") {
 448                 document.getElementById("docs_content").innerHTML = document.getElementById("docs_examples").innerHTML;
 449         } else if(page == "examples2") {
 450                 document.getElementById("docs_content").innerHTML = document.getElementById("docs_examples2").innerHTML;
 451         } else {
 452                 document.getElementById("docs_content").innerHTML = document.getElementById("docs_main").innerHTML;
 453         }
 454 }
 455
 456 </script>
 457
 458 <style type="text/css">
 459
 460 body {
 461         font-family: Tahoma, Arial, Helvetica, sans-serif;
 462 }
 463
 464 #disp_pointer {
 465         float:right;
 466         color: #f00;
 467 }
 468
 469 #code_buttons {
 470         position: absolute;
 471         top: 570px;
 472         left: 10px;
 473 }
 474
 475 #input_banner {
 476         position: absolute;
 477         top: 120px;
 478         left: 10px;
 479 }
 480
 481 #da_banner {
 482         position: absolute;
 483         top: 360px;
 484         left: 625px;
 485 }
 486
 487 #ref_banner {
 488         position: absolute;
 489         top: 410px;
 490         left: 625px;
 491 }
 492
 493 #ip_banner {
 494         position: absolute;
 495         top: 315px;
 496         left: 625px;
 497 }
 498
 499 #output_banner {
 500         position: absolute;
 501         top: 120px;
 502         left: 625px;
 503 }
 504
 505 #memory_banner {
 506         position: absolute;
 507         top: 120px;
 508         left: 315px;
 509 }
 510
 511 #input {
 512         position: absolute;
 513         top: 140px;
 514         left: 10px;
 515 }
 516
 517 #ram_disp {
 518         position: absolute;
 519         top: 140px;
 520         left: 315px;
 521 }
 522
 523 #memory_table {
 524         border:1px solid #000;
 525         border-collapse: collapse;
 526 }
 527
 528 .even td {
 529         padding: 4px;
 530         border-bottom:1px solid #000;
 531 }
 532
 533 .odd td {
 534         padding: 4px;
 535         background-color: #def;
 536         border-bottom: 1px solid #000;
 537 }
 538
 539 .addr {
 540         color: #00f;
 541 }
 542
 543 .ram {
 544         border-right:1px solid #000;
 545 }
 546
 547 #output {
 548         position: absolute;
 549         top: 140px;
 550         left: 625px;
 551 }
 552
 553 #docs {
 554         border:1px solid #000;
 555         background-color: #dfd;
 556         position: absolute;
 557         top: 10px;
 558         left: 10px;
 559         width: 1000px;
 560         height:700px;
 561         visibility: hidden;
 562 }
 563
 564 #docs_top_banner {
 565         color: #fff;
 566         background-color: #88f;
 567         border-bottom:1px solid #000;
 568         position: absolute;
 569         top: 0px;
 570         left: 0px;
 571         height: 25px;
 572         padding-top: 5px;
 573         padding-left: 5px;
 574         width: 995px;
 575 }
 576
 577 #docs_close_btn {
 578         background-color: #f00;
 579         border:3px solid #000;
 580         position: absolute;
 581         top: 0px;
 582         right: 0px;
 583         height: 25px;
 584         cursor: pointer;
 585 }
 586
 587 #docs_mnu_btn {
 588         border:2px solid #000;
 589         background-color: #faa;
 590         color: #000;
 591         position: absolute;
 592         top: 0px;
 593         left: 375px;
 594         height: 25px;
 595         padding-top: 3px;
 596         padding-left: 20px;
 597         padding-right: 20px;
 598         cursor: pointer;
 599 }
 600
 601 #docs_content {
 602         position: absolute;
 603         top: 35px;
 604         padding: 10px;
 605 }
 606
 607 #docs_link:hover {
 608         background-color: #faa;
 609         cursor: pointer;
 610
 611 }
 612
 613 .docs_code_ex {
 614         background-color: #fff;
 615         border: 1px solid #ddd;
 616         padding: 5px;
 617 }
 618
 619 .docs_hidden {
 620         visibility: hidden;
 621 }
 622
 623 #instruction {
 624         position: absolute;
 625         top: 335px;
 626         left: 625px;
 627 }
 628
 629 #data {
 630         position: absolute;
 631         top: 385px;
 632         left: 625px;
 633 }
 634
 635 #reference {
 636         position: absolute;
 637         top: 430px;
 638         left: 625px;
 639         width: 280px;
 640 }
 641
 642 </style>
 643 <body onLoad="init_form();">
 644
 645 <center><h2>Turing Tarpit Simulator</h2></center>
 646
 647 <center>
 648 <button onClick='reset();'><img src="http://opentextbook.info/icons/32x32/resultset_first.png"></button>
 649 &nbsp;&nbsp;
 650 <button onClick='step_back();'><img src="http://opentextbook.info/icons/32x32/resultset_previous.png"></button>
 651 &nbsp;&nbsp;
 652 <button onClick='step_next();'><img src="http://opentextbook.info/icons/32x32/resultset_next.png"></button>
 653 &nbsp;&nbsp;
 654 <button onClick='run();'><img src="http://opentextbook.info/icons/32x32/resultset_last.png"></button>
 655 &nbsp;&nbsp;
 656 <button onClick='halt();'><img src="http://opentextbook.info/icons/32x32/cancel.png"></button>
 657 &nbsp;&nbsp;
 658 <button disabled><img src="http://opentextbook.info/icons/32x32/disk.png"></button>
 659 &nbsp;&nbsp;
 660 <button onClick='display_docs();'><img src="http://opentextbook.info/icons/32x32/book_open.png"></button>
 661 </center>
 662
 663 <div id="code_buttons">
 664 <button id="dbg_status" onClick='debug_toggle_breakpoints();'>
 665         <img src="http://opentextbook.info/icons/32x32/bug_add.png">
 666 </button>
 667 &nbsp;&nbsp;
 668 <button id="dbg_status" onClick='debug_remove_breakpoints();'>
 669         <img src="http://opentextbook.info/icons/32x32/bin.png">
 670 </button>
 671 </div>
 672
 673 <div id="input_banner">INPUT</div>
 674 <div id="input"><textarea id="code" rows="27" cols="38"></textarea></div>
 675
 676 <div id="ip_banner">INSTRUCTION POINTER</div>
 677 <div id="instruction"><input  onBlur="ins_point_modify_by_address(disp_ins_pointer.value);" id="ins_pointer_disp" type="text" diabled value=0></div>
 678
 679 <div id="da_banner">DATA POINTER</div>
 680 <div id="data"><input onBlur="dat_point_modify_by_address(disp_dat_pointer.value);" id="dat_pointer_disp" type="text" diabled value=0></div>
 681
 682 <div id="ref_banner">INSTRUCTION REFERENCE</div>
 683 <table id="reference">
 684         <tr><td>+</td><td>increment byte at data pointer</td></tr>
 685         <tr><td>-</td><td>decrement byte at data pointer</td></tr>
 686         <tr><td>></td><td>increment data pointer</td></tr>
 687         <tr><td><</td><td>decrement data pointer</td></tr>
 688         <tr><td>.</td><td>print byte at data pointer</td></tr>
 689         <tr><td>,</td><td>accept one byte of input</td></tr>
 690         <tr><td>*</td><td>set breakpoint</td></tr>
 691 </table>
 692
 693 <div id="memory_banner">MEMORY</div>
 694 <div id="ram_disp"></div>
 695 <div id="output_banner">OUTPUT</div>
 696 <div id="output">
 697 <textarea name=code id=output_disp rows="10" cols="38" disabled ></textarea>
 698 </div>
 699 <div id="docs">
 700         <div id="docs_top_banner">
 701                 Turing Tarpit Simulator Documentation&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 702                 <div id="docs_mnu_btn" onClick="docs_select('main');">Main Menu</div>
 703                 <div id="docs_close_btn" onClick="hide_docs();">X</div></div>
 704
 705         <div id="docs_content"></div>
 706 </div>
 707
 708 <div id="docs_main" class="docs_hidden">
 709                 <div id="docs_link" onClick="docs_select('basic');">Basic Operation</div>
 710                 <div id="docs_link" onClick="docs_select('features');">Features and Hints</div>
 711                 <div id="docs_link" onClick="docs_select('examples');">Example Code 1</div>
 712                 <div id="docs_link" onClick="docs_select('examples2');">Example Code 2</div>
 713
 714 </div>
 715
 716 <div id="docs_basic" class="docs_hidden">
 717
 718 Basic
 719
 720 <p>This program is completely self contained in one HTML document.  You are free do use it how you wish, subject to the terms and conditions of the GNU GPL license (version 3).
 721
 722 <p>Although it has not been tested in all browsers, it should work well under most any modern web browser that supports Dynamic HTML and JavaScript.  You must have JavaScript enabled for this application to work properly.
 723
 724 <p>No server interaction or outside service is needed for this program to operate.
 725
 726 </div>
 727
 728 <div id="docs_features" class="docs_hidden">
 729
 730 Features and Hints
 731
 732 <p>All characters outside the Instruction Set are considered comments and will be skipped over during runtime.
 733
 734 <p>While program executes, the Input cursor is moved over the current instruction.
 735
 736 <p>User can change the address of the Data Pointer and Instruction Pointer at any time.
 737 Memory and pointers that have been modified are highlighted in yellow until the next step.
 738
 739 <p>The Data Pointer can point to any location. If you de-reference a pointer out of memory range, a segfault error will occur. This causes the computer to reboot without warning.
 740
 741 <p>The Instruction Pointer can point to a location range of 1 to the number of characters in the input.
 742
 743 <p>Restarting the machine will reset all Memory, Data and Instruction Pointers to zero.
 744
 745 <p>The output of the program cannot be edited.
 746
 747 <p>A user can add a break instruction in the code using an asterisk '*'. This will cause the machine to pause when in Run Mode. Breaks can be disabled and enabled with the debug button, and can be permanently deleted with the delete button.
 748
 749 <p>In this version the programs you type in are not saved to your computer.  This must be done as a manual operation.
 750
 751 <p>As this program is reliant on the speed and efficiency of your browsers JavaScript implementation some computers will be able to execute programs faster than others.
 752
 753 </div>
 754
 755 <div id="docs_examples" class="docs_hidden">
 756 These are some examples of programs and snippets to get you started. Click the "Load" button to apply these to the Input of the simulator. (Please Note: You will erase the current program stored there.) Many of these examples can be found at Wikipedia.
 757
 758 <p><b>Clear Byte:</b>
 759 Sets value at current Data Pointer to Zero.
 760 <div class=docs_code_ex>
 761 [-]
 762 </div>
 763 <p><b>Clear Previous Cells:</b>
 764 Sets value of all previous bytes including current byte to Zero.
 765 <div class=docs_code_ex>
 766 [[-]<]
 767 </div>
 768 <p><b>Rewind:</b>
 769 Goes back to byte Zero.
 770 <div class=docs_code_ex>
 771 [<]>
 772 </div>
 773 <p><b>Fast-forward:</b>
 774 Increments the data pointer until a 0 is found then decrements if until the current cell is non-zero.
 775 <div class=docs_code_ex>
 776 [>]<
 777 </div>
 778 <p><b>Simple Loop:</b>
 779 Accepts input from the user and echos it to the screen, similar to the UNIX cat program.
 780 <div class=docs_code_ex>
 781  ,[.,]
 782 </div>
 783 <p><b>Moving the Data Pointer:</b>
 784 Accepts input from the user and saves all input in the memory for future use.
 785 <div class=docs_code_ex>
 786  >,[.>,]
 787 </div>
 788 </div>
 789
 790
 791 <div id="docs_examples2" class="docs_hidden">
 792 <p><b>Add Two Bytes:</b>
 793 Adds current location to the next location and leaves behind a Zero for the first value.
 794 <div class=docs_code_ex>
 795 [->+<]
 796 </div>
 797 <p><b>Lower To Upper:</b>
 798 Accepts lower case input from the user and makes it uppercase. Stops when user presses the enter key.
 799 <div class=docs_code_ex>
 800 ,----------[----------------------.,----------]
 801 </div>
 802 <p><b>Copy Value:</b>
 803 Copy value of byte Zero to byte One.
 804 <div class=docs_code_ex>
 805 >[-]>[-]<<[->+>+<<]>>[-<<+>>]<<
 806 </div>
 807 <p><b>Seek:</b>
 808 Move Data Pointer forward until it lands on a byte with a value of 1, preserving all bytes it passes.
 809 <div class=docs_code_ex>
 810 -[+>-]+
 811 </div>
 812 <p><b>Single Digit Add:</b>
 813 Adds two single digit numbers and display result. Works on one-digit results only.
 814 <div class=docs_code_ex>
 815 ,>++++++[<-------->-],[<+>-]<.
 816 </div>
 817 <p><b>Single Digit Multiplication:</b>
 818 Multiply two single digit numbers and display result. Works on one-digit results only.
 819 <div class=docs_code_ex>
 820  ,>,>++++++++[<------<------>>-]
 821  <<[>[>+>+<<-]>>[<<+>>-]<<<-]
 822  >>>++++++[<++++++++>-]<.>.
 823 </div>
 824 <p><b>Single Digit Division:</b>
 825 Accepts two single-digit numbers from the user, divides them and displays the truncated quotient. Dividend is stored in byte Zero and Divisor is stored in byte One.
 826 <div class=docs_code_ex>
 827 ,>,>++++++[-<--------<-------->>]<<[>[->+>+<<]>[-<<-[>]>>>[<[>>>-<<<[-]]>>]<<]>>>+<<[-<<+>>]<<<]>[-]>>>>[-<<<<<+>>>>>]<<<<++++++[-<++++++++>]<.
 828 </div>
 829 </div>
 830 </body>
 831 </html>
 832