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 ins_pointer_changed = 0;    /* bool set to 1 if ins pointer has changed in the last step */
   8 var ins_pointer_last_address = 0;       /* address of ins pointer in last step */
   9 var dat_pointer = 0;                    /* data pointer */
  10 var dat_pointer_changed = 0;            /* bool set to 1 if data pointer has changed in the last step */
  11 var dat_pointer_last_address = 0;       /* address of data pointer in last step */
  12 var ram_last_address = 0;               /* address of RAM updated in last step */
  13 var breakpoints = 1;                    /* bool set to 0 to ignore breakpoints */
  14 var ram = new Array();                  /* memory of virtual machine */
  15 var jmp = new Array();                  /* used as a stack to jump from one command to another */
  16 var ins = null;                         /* current instruction from code */
  17 var halt = false;                       /* halts program ASAP */
  18
  19 /* objects that display data to the user */
  20 var disp_docs;
  21 var disp_code;
  22 var disp_ram;
  23 var disp_ins_pointer;
  24 var disp_dat_pointer;
  25 var disp_pointer = "<div id=disp_pointer>&#8658;</div>"; /* data pointer displayed in memory block */
  26
  27 /* select all contents of this input for the convenience of the user */
  28 function select_all(e)
  29 {
  30         document.getElementById(e).focus();
  31         document.getElementById(e).select();
  32 }
  33
  34 /* highlight current instruction running on machine */
  35 function code_highlight(inputEl, selStart, selEnd)
  36 {
  37         if (inputEl.setSelectionRange) {
  38                 inputEl.focus();
  39                 inputEl.setSelectionRange(selStart, selEnd);
  40         } else if (inputEl.createTextRange) {
  41                 var range = inputEl.createTextRange();
  42                 range.collapse(true);
  43                 range.moveEnd('character', selEnd);
  44                 range.moveStart('character', selStart);
  45                 range.select();
  46         }
  47 }
  48
  49 /* turns breakpoints on and off */
  50 function debug_toggle_breakpoints()
  51 {
  52         var button = document.getElementById("dbg_status");
  53         if(breakpoints) {
  54                 breakpoints=0;
  55                 button.innerHTML='<img src="http://opentextbook.info/icons/32x32/bug_delete.png">';
  56         }else {
  57                 breakpoints=1;
  58                 button.innerHTML='<img src="http://opentextbook.info/icons/32x32/bug_add.png">';
  59         }
  60 }
  61
  62 /* removes all breakpoints in source code */
  63 function debug_remove_breakpoints()
  64 {
  65         /* ask user for permission first */
  66         var ans = confirm("Permanently remove all breakpoints from code?");
  67         var code = document.getElementById("code");
  68         if(ans) { code.value = code.value.replace( /\*/g , '' ); }
  69 }
  70
  71 /* test current code character - return true if it is an instruction */
  72 /* tried to use regex on this and could not get it to work :( */
  73 function tst_inst()
  74 {
  75         if(ins == '+' ||  ins == '-' ||  ins == '>' ||  ins == '<' ||
  76           ins == '*' ||  ins == '.' ||  ins == '[' ||  ins == ']' ||  ins == ',') {
  77                 return true;
  78         }
  79         return false;
  80 }
  81
  82 /* find next instruction in code and move instruction pointer to it */
  83 function fnd_nxt_inst()
  84 {
  85         do {
  86                 if(ins_pointer > disp_code.value.length) { break; } /* must stop at end of code */
  87                 update_ins_pointer(1);
  88                 ins = disp_code.value.substring(ins_pointer-1,ins_pointer); /* get data at ins_pointer location */
  89         }while(!tst_inst());
  90         if(ins_pointer > disp_code.value.length) {
  91                 alert("HALT: Program is Complete");
  92                 halt = true;
  93                 reset();
  94         }
  95
  96         /* highlight code currently executing on screen */
  97         code_highlight(disp_code, ins_pointer-1, ins_pointer);
  98 }
  99
 100 /* find previous instruction in code and move instruction pointer to it */
 101 function fnd_prv_inst()
 102 {
 103         ins_pointer--;
 104         while(ins_pointer >= 0)
 105         {
 106                 ins = disp_code.value.substring(ins_pointer-1, ins_pointer); /* get data at ins_pointer location */
 107                 if(tst_inst()) { return; }
 108                 ins_pointer--;
 109         }
 110         if(ins_pointer == 0) {
 111                 alert("SEGFAULT: Program could not find corresponding jump instruction");
 112                 halt = true;
 113                 reset();
 114         }
 115 }
 116
 117 /* execute next instruction from input */
 118 function exe_nxt_inst()
 119 {
 120         var temp_count = 0;
 121         fnd_nxt_inst();
 122         switch(ins)
 123         {
 124                 case '+':
 125                         ram_modify(dat_pointer, 1);
 126                         break;
 127                 case '-':
 128                         ram_modify(dat_pointer, -1);
 129                         break;
 130                 case '>':
 131                         dat_point_modify(1);
 132                         break;
 133                 case '<':
 134                         dat_point_modify(-1);
 135                         break;
 136                 case '*': /* these are comments - a break from the standard language */
 137                         if(breakpoints) { stop(); }
 138                         break;
 139                 case '.':
 140                         print_mem();
 141                         break;
 142                 case '[':
 143                         jump_fwd();
 144                         break;
 145                 case ']':
 146                         jump_bak();
 147                         break;
 148                 case ',':
 149                         get_byte();
 150                         break;
 151                 default:
 152                         /* must be a comment :) */
 153         }
 154 }
 155
 156 /* if byte at data pointer is = 0, jump forward to instruction after matching ']' command */
 157 function jump_fwd()
 158 {
 159         if(ram[dat_pointer] != 0) { return; }
 160         /* add this jump to stack */
 161         jmp.push('[');
 162         /* loop through code, pushing and popping stack until stack is empty */
 163         while(jmp.length > 0) {
 164                 fnd_nxt_inst();
 165                 if(ins == ']') { jmp.pop();
 166                 } else if (ins == '[') { jmp.push(']'); }
 167         }
 168 }
 169
 170 /* if byte at data pointer is != 0, jump back to instruction after matching '[' command */
 171 function jump_bak()
 172 {
 173         if(ram[dat_pointer] == 0) { return; }
 174         /* add this jump to stack */
 175         jmp.push(']');
 176         /* loop through code, pushing and popping stack until stack is empty */
 177         while(jmp.length > 0 && ins_pointer > 0) {
 178                 fnd_prv_inst();
 179                 if(ins == '[') { jmp.pop();
 180                 } else if (ins == ']') { jmp.push(']'); }
 181         }
 182 }
 183
 184 /* get single byte of input from the user */
 185 function get_byte()
 186 {
 187         var b = prompt("Please Single Byte of Data","");
 188         alert(b);
 189         ram_set(dat_pointer, b.charCodeAt(b));
 190 }
 191
 192 /*
 193         rewind code to beginning reset all memory locations
 194         this simulates rebooting the computer
 195 */
 196 function reset()
 197 {
 198         update_ins_pointer(0);
 199         dat_point_modify(0);
 200         ram_reset();
 201         ram_highlight_clear();
 202         dat_point_highlight();
 203         document.getElementById("output_disp").innerHTML = '';
 204         document.getElementById("addr_0").innerHTML = "0" + disp_pointer;
 205         disp_ins_pointer.style.backgroundColor = "#fff";
 206         dat_point_highlight_clear();
 207         code_highlight(disp_code, 0, 1);
 208 }
 209
 210 /* stop stepping through code on timer if breakpoints enabled */
 211 function stop()
 212 {
 213         halt = true;
 214 }
 215
 216 /* run through program on timer, stopping at breakpoints if enabled */
 217 function run()
 218 {
 219         var total_steps = document.getElementById("code").value.length;
 220         halt = false; /* seems weird, but this is the only way to make the halt work */
 221         while(ins_pointer <= total_steps && halt == false) { step_next(); }
 222 }
 223
 224 /* step forward one instruction */
 225 function step_next()
 226 {
 227         //update_ins_pointer(1);
 228         exe_nxt_inst();
 229         dat_point_highlight();
 230 }
 231
 232 /* more back one instruction - undoes work of previous instruction */
 233 function step_back()
 234 {
 235         update_ins_pointer(-1);
 236         dat_point_highlight();
 237 }
 238
 239 /* update instruction pointer
 240         direction:
 241
 242         1 increment pointer by one
 243         0 set pointer to 0
 244         -1 decrement pointer by one
 245 */
 246 function update_ins_pointer(direction)
 247 {
 248         if(direction < 0 && ins_pointer != 0 ) { ins_pointer--; }
 249         else if (direction == 0 ) { ins_pointer = 0; }
 250         else { ins_pointer++; }
 251         disp_ins_pointer.value =  ins_pointer;
 252         ins_pointer_changed = 1;
 253         ins_point_highlight();
 254 }
 255
 256 /* update instruction pointer and set to new value */
 257 function ins_point_modify_by_address(val)
 258 {
 259         /* instruction pointer can never be less than 0 */
 260         if(val < 0) {
 261                 alert("Instruction Pointer cannot be set less than Zero.");
 262                 disp_ins_pointer.value =  ins_pointer; /* reset val to previous */
 263                 return;
 264         }
 265         if(val > disp_code.value.length) {
 266                 alert("Instruction Pointer cannot be set beyond end of code.\n Current length of code: " + disp_code.value.length);
 267                 disp_ins_pointer.value =  ins_pointer; /* reset val to previous */
 268                 return;
 269         }
 270         ins_pointer = disp_ins_pointer.value;
 271         if(ins_pointer_last_address != ins_pointer) { ins_pointer_changed = 1; }
 272         ins_point_highlight();
 273 }
 274
 275 /* turns on and off data pointer highlight if it has changed this step */
 276 function ins_point_highlight()
 277 {
 278         if(ins_pointer_changed) {
 279                 disp_ins_pointer.style.backgroundColor = "#ff0";
 280                 ins_pointer_changed = 0;
 281         } else {
 282                 disp_ins_pointer.style.backgroundColor = "#fff";
 283         }
 284 }
 285
 286 /* setup virtual machine - must be called on page load */
 287 function init_form()
 288 {
 289         disp_code  = document.getElementById("code");
 290         disp_ins_pointer = document.getElementById("ins_pointer_disp");
 291         disp_dat_pointer = document.getElementById("dat_pointer_disp");
 292         disp_ram = document.getElementById("ram_disp");
 293         ram_reset();
 294         ram_init();
 295         document.getElementById("addr_0").innerHTML = "0" + disp_pointer;
 296         disp_docs = document.getElementById("docs");
 297         /* reset_output(); */
 298 }
 299
 300 /* reset all RAM to 0 */
 301 function ram_reset()
 302 {
 303         var i;
 304         for(i=0; i < 64; i++) { ram[i] = 0; }
 305 }
 306
 307 /* update highlight of one memory address and release other highlight if needed */
 308 function ram_highlight(address)
 309 {
 310         var disp_last_address = document.getElementById("ram_"+ram_last_address);
 311         /* highlight background of current address */
 312         document.getElementById("ram_"+address).style.backgroundColor = "#ff0";
 313
 314         /* remove highlight from last address modified */
 315         if(ram_last_address != address){
 316                 if(ram_last_address%2==0) {
 317                         disp_last_address.style.backgroundColor = "#fff";
 318                 } else {
 319                         disp_last_address.style.backgroundColor = "#def";
 320                 }
 321         }
 322 }
 323
 324 /* remove highlight from all memory cells regardless of current status */
 325 function ram_highlight_clear()
 326 {
 327         var i;
 328         for(i=0; i < 64; i++)
 329         {
 330                 if(i%2==0) {
 331                         document.getElementById("ram_"+i).style.backgroundColor = "#fff";
 332                 } else {
 333                         document.getElementById("ram_"+i).style.backgroundColor = "#def";
 334                 }
 335                 document.getElementById("ram_"+i).innerHTML = ram[i];
 336         }
 337 }
 338
 339 /* define RAM on screen */
 340 function ram_init()
 341 {
 342         var i;
 343         var table = "<table id=memory_table>\n";
 344         for(i=0; i < 16; i++){
 345                 if(i%2==0) {
 346                         table += "\t<tr class=even>";
 347                 } else {
 348                         table += "\t<tr class=odd>";
 349                 }
 350                 table += "<td width='35' class=addr id=addr_"+i+">"+i+"</td><td width='35' class=ram id=ram_"+i+">"+ram[i]+"</td>";
 351                 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";
 352                 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";
 353                 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";
 354         }
 355         table +=  "</table>\n";
 356         disp_ram.innerHTML = table;
 357 }
 358
 359 /*
 360         modify the value at this address - reset RAM highlights for all addresses
 361         1 increment RAM by one
 362         0 set RAM to 0
 363         -1 decrement RAM by one
 364 */
 365 function ram_modify(address, change)
 366 {
 367         if(address < 0 || address > 63) {
 368                 alert("SEGFAULT: Cannot Modify Data Outside of Memory Range");
 369                 halt = true;
 370                 reset();
 371                 return;
 372         }
 373
 374         if (change > 0 ) {
 375                 ram[address]++;
 376         } else if(change < 0 ) {
 377                 ram[address]--;
 378         } else {
 379                 ram[address] = 0;
 380         }
 381         ram_highlight(address);
 382         document.getElementById("ram_"+address).innerHTML = ram[address];
 383         ram_last_address = address;
 384 }
 385
 386 /* modify one byte of memory - set to address */
 387 function ram_set(address, val)
 388 {
 389         if(address < 0 || address > 63) {
 390                 alert("SEGFAULT: Cannot Modify Data Outside of Memory Range");
 391                 halt = true;
 392                 reset();
 393                 return;
 394         }
 395
 396         ram[address] = val;
 397         ram_highlight(address);
 398         document.getElementById("ram_"+address).innerHTML = ram[address];
 399         ram_last_address = address;
 400 }
 401
 402 /*
 403         modify state of data pointer
 404         1 increment data pointer by one
 405         0 set data pointer to 0
 406         -1 decrement data pointer by one
 407
 408 */
 409 function dat_point_modify(change)
 410 {
 411         dat_pointer_last_address = dat_pointer;
 412         if (change > 0 ) {
 413                 dat_pointer++;
 414         } else if(change < 0 ) {
 415                 /* could put SEGFAULT here, but C does not have a check for this, so neither will I ;) */
 416                 dat_pointer--;
 417         } else {
 418                 dat_pointer = 0;
 419         }
 420
 421         /* place '>' char next to memory address in table */
 422         if(dat_pointer >= 0 && dat_pointer < 64) {
 423                 document.getElementById("addr_"+dat_pointer).innerHTML = dat_pointer + disp_pointer;
 424         }
 425
 426         /* remove '>' char next to memory address in table */
 427         if(dat_pointer_last_address >= 0 && dat_pointer_last_address < 64) {
 428                 document.getElementById("addr_"+dat_pointer_last_address).innerHTML = dat_pointer_last_address;
 429         }
 430
 431         disp_dat_pointer.value = dat_pointer;
 432         dat_pointer_changed = 1;
 433 }
 434
 435 function dat_point_modify_by_address(val)
 436 {
 437         dat_pointer_last_address = dat_pointer;
 438         dat_pointer = disp_dat_pointer.value;
 439         /* place '>' char next to memory address in table */
 440         if(dat_pointer >= 0 && dat_pointer < 64) {
 441                 document.getElementById("addr_"+dat_pointer).innerHTML = dat_pointer + disp_pointer;
 442         }
 443
 444         /* remove '>' char next to memory address in table */
 445         if(dat_pointer_last_address >= 0 && dat_pointer_last_address < 64) {
 446                 document.getElementById("addr_"+dat_pointer_last_address).innerHTML = dat_pointer_last_address;
 447         }
 448         dat_pointer_changed = 1;
 449         dat_point_highlight();
 450 }
 451
 452 /* turns on and off data pointer highlight if it has changed this step */
 453 function dat_point_highlight()
 454 {
 455         if(dat_pointer_changed) {
 456                 disp_dat_pointer.style.backgroundColor = "#ff0";
 457                 dat_pointer_changed = 0;
 458         } else {
 459                 disp_dat_pointer.style.backgroundColor = "#fff";
 460         }
 461
 462         /* as a convenience to the user, set to red if pointer is out of memory range */
 463         if(dat_pointer < 0 || dat_pointer > 63) {
 464                 disp_dat_pointer.style.backgroundColor = "#f00";
 465         }
 466 }
 467
 468 /* remove highlight from data pointer */
 469 function dat_point_highlight_clear()
 470 {
 471         disp_dat_pointer.style.backgroundColor = "#fff";
 472 }
 473
 474 /* print ASCII representation of memory at data pointer */
 475 function print_mem()
 476 {
 477         var x = String.fromCharCode(ram[dat_pointer]);
 478         document.getElementById("output_disp").innerHTML += x;
 479 }
 480
 481 /* documentation stored inside invisible div. This shows its contents. */
 482 function display_docs()
 483 {
 484         disp_docs.style.visibility = "visible";
 485         docs_select("docs_main");
 486 }
 487
 488 /* hide documentation from user */
 489 function hide_docs()
 490 {
 491         disp_docs.style.visibility = "hidden";
 492 }
 493
 494 function docs_select(page)
 495 {
 496         if(page == "basic") {
 497                 document.getElementById("docs_content").innerHTML = document.getElementById("docs_basic").innerHTML;
 498         } else if(page == "features") {
 499                 document.getElementById("docs_content").innerHTML = document.getElementById("docs_features").innerHTML;
 500         } else if(page == "examples") {
 501                 document.getElementById("docs_content").innerHTML = document.getElementById("docs_examples").innerHTML;
 502         } else if(page == "examples2") {
 503                 document.getElementById("docs_content").innerHTML = document.getElementById("docs_examples2").innerHTML;
 504         } else if(page == "ascii") {
 505                 document.getElementById("docs_content").innerHTML = document.getElementById("docs_ascii").innerHTML;
 506         } else {
 507                 document.getElementById("docs_content").innerHTML = document.getElementById("docs_main").innerHTML;
 508         }
 509 }
 510
 511 /*
 512
 513 allows user to kick off example from the help menu.
 514 closes documentation menu, overwrites code with example.
 515 prints error message if something goes wrong.
 516
 517 */
 518 function docs_try(ex)
 519 {
 520         var ans = confirm("This will delete code currently loaded in machine.");
 521         if(!ans) { return; }
 522         hide_docs();                    /* close documentation window */
 523         reset();                                /* reset computer */
 524         if(ex == null) { alert("Example not setup correctly."); return; }
 525         disp_code.innerHTML = document.getElementById(ex).innerHTML;                            /* write data out to code textarea */
 526 }
 527
 528 </script>
 529
 530 <style type="text/css">
 531
 532 body {
 533         font-family: Tahoma, Arial, Helvetica, sans-serif;
 534 }
 535
 536 #disp_pointer {
 537         float:right;
 538         color: #f00;
 539 }
 540
 541 #code_buttons {
 542         position: absolute;
 543         top: 570px;
 544         left: 10px;
 545 }
 546
 547 #input_banner {
 548         position: absolute;
 549         top: 120px;
 550         left: 10px;
 551 }
 552
 553 #da_banner {
 554         position: absolute;
 555         top: 360px;
 556         left: 625px;
 557 }
 558
 559 #ref_banner {
 560         position: absolute;
 561         top: 410px;
 562         left: 625px;
 563 }
 564
 565 #ip_banner {
 566         position: absolute;
 567         top: 315px;
 568         left: 625px;
 569 }
 570
 571 #output_banner {
 572         position: absolute;
 573         top: 120px;
 574         left: 625px;
 575 }
 576
 577 #memory_banner {
 578         position: absolute;
 579         top: 120px;
 580         left: 315px;
 581 }
 582
 583 #input {
 584         position: absolute;
 585         top: 140px;
 586         left: 10px;
 587 }
 588
 589 #ram_disp {
 590         position: absolute;
 591         top: 140px;
 592         left: 315px;
 593 }
 594
 595 #memory_table {
 596         border:1px solid #000;
 597         border-collapse: collapse;
 598 }
 599
 600 .even td {
 601         padding: 4px;
 602         border-bottom:1px solid #000;
 603 }
 604
 605 .odd td {
 606         padding: 4px;
 607         background-color: #def;
 608         border-bottom: 1px solid #000;
 609 }
 610
 611 .addr {
 612         color: #00f;
 613 }
 614
 615 .ram {
 616         border-right:1px solid #000;
 617 }
 618
 619 #output {
 620         position: absolute;
 621         top: 140px;
 622         left: 625px;
 623 }
 624
 625 #docs {
 626         border:1px solid #000;
 627         background-color: #fff;
 628         position: absolute;
 629         top: 10px;
 630         left: 10px;
 631         width: 950px;
 632         height:700px;
 633         visibility: hidden;
 634 }
 635
 636 #docs_top_banner {
 637         color: #000;
 638         background-color: #def;
 639         border-bottom:1px solid #000;
 640         position: absolute;
 641         top: 0px;
 642         left: 0px;
 643         height: 25px;
 644         padding-top: 5px;
 645         padding-left: 5px;
 646         width: 945px;
 647 }
 648
 649 #docs_close_btn {
 650         background: #fff;
 651         border:1px solid #000;
 652         position: absolute;
 653         top: 0px;
 654         right: 0px;
 655         cursor: pointer;
 656         padding: 6px;
 657 }
 658
 659 #docs_mnu_btn {
 660         border:2px solid #000;
 661         color: #000;
 662         position: absolute;
 663         top: 0px;
 664         left: 375px;
 665         padding-top: 3px;
 666         padding-left: 20px;
 667         padding-right: 20px;
 668 }
 669
 670 #docs_content {
 671         position: absolute;
 672         top: 35px;
 673         padding: 10px;
 674 }
 675
 676 #docs_link:hover {
 677         background-color: #faa;
 678         cursor: pointer;
 679
 680 }
 681
 682 .docs_code_ex {
 683         background-color: #def;
 684         border: 1px solid #ddd;
 685         padding: 5px;
 686 }
 687
 688 .docs_hidden {
 689         visibility: hidden;
 690 }
 691
 692 #instruction {
 693         position: absolute;
 694         top: 335px;
 695         left: 625px;
 696 }
 697
 698 #data {
 699         position: absolute;
 700         top: 385px;
 701         left: 625px;
 702 }
 703
 704 #ascii {
 705         border-collapse: collapse;
 706         border: 1px solid #ddd;
 707 }
 708
 709 #reference {
 710         border-collapse: collapse;
 711         border: 1px solid #ddd;
 712         position: absolute;
 713         top: 430px;
 714         left: 625px;
 715         width: 280px;
 716 }
 717
 718 .ref_even td {
 719         border-bottom: 1px solid #ddd;
 720 }
 721
 722 .ref_odd td {
 723         border-bottom: 1px solid #ddd;
 724         background-color: #def;
 725 }
 726
 727 .ref_ins {
 728         font-size: 18px;
 729         font-weight:bold;
 730         color: #00f;
 731 }
 732
 733 </style>
 734 <body onLoad="init_form();">
 735
 736 <center><h2>Turing Tarpit Simulator</h2></center>
 737
 738 <center>
 739 <button onClick='reset();'><img src="http://opentextbook.info/icons/32x32/resultset_first.png" title="Restart" alt="Restart"></button>
 740 &nbsp;&nbsp;
 741 <button onClick='step_back();'><img src="http://opentextbook.info/icons/32x32/resultset_previous.png" title="Step Back" alt="Step Back"></button>
 742 &nbsp;&nbsp;
 743 <button onClick='step_next();'><img src="http://opentextbook.info/icons/32x32/resultset_next.png" title="Next Step" alt="Next Step"></button>
 744 &nbsp;&nbsp;
 745 <button onClick='run();'><img src="http://opentextbook.info/icons/32x32/resultset_last.png" title="Run" alt="Run"></button>
 746 &nbsp;&nbsp;
 747 <button onClick='halt();'><img src="http://opentextbook.info/icons/32x32/cancel.png" title="Halt Execution" alt="Halt Execution"></button>
 748 &nbsp;&nbsp;
 749 <button disabled><img src="http://opentextbook.info/icons/32x32/disk.png" title="Save Code" alt="Save Code"></button>
 750 &nbsp;&nbsp;
 751 <button onClick='display_docs();'><img src="http://opentextbook.info/icons/32x32/book_open.png" title="Open Documentation" alt="Open Documentation"></button>
 752 </center>
 753
 754 <div id="code_buttons">
 755 <button id="dbg_status" onClick='debug_toggle_breakpoints();'  title="Enable/Disable Breakpoints" alt="Enable/Disable Breakpoints">
 756         <img src="http://opentextbook.info/icons/32x32/bug_add.png">
 757 </button>
 758 &nbsp;&nbsp;
 759 <button id="dbg_status" onClick='debug_remove_breakpoints();'  title="Remove Breakpoints" alt="Remove Breakpoints">
 760         <img src="http://opentextbook.info/icons/32x32/bin.png">
 761 </button>
 762 </div>
 763
 764 <div id="input_banner">INPUT</div>
 765 <div id="input"><textarea id="code" rows="27" cols="38"></textarea></div>
 766
 767 <div id="ip_banner">INSTRUCTION POINTER</div>
 768 <div id="instruction"><input onClick="select_all('ins_pointer_disp');" onBlur="ins_point_modify_by_address(disp_ins_pointer.value);" id="ins_pointer_disp" type="text" diabled value=0></div>
 769
 770 <div id="da_banner">DATA POINTER</div>
 771 <div id="data"><input  onClick="select_all('dat_pointer_disp');" onBlur="dat_point_modify_by_address(disp_dat_pointer.value);" id="dat_pointer_disp" type="text" diabled value=0></div>
 772
 773 <div id="ref_banner">INSTRUCTION REFERENCE</div>
 774 <table id="reference">
 775         <tr class="ref_even"><td class="ref_ins">+</td><td>increment byte at data pointer</td></tr>
 776         <tr class="ref_odd" ><td class="ref_ins">-</td><td>decrement byte at data pointer</td></tr>
 777         <tr class="ref_even"><td class="ref_ins">></td><td>increment data pointer</td></tr>
 778         <tr class="ref_odd" ><td class="ref_ins"><</td><td>decrement data pointer</td></tr>
 779         <tr class="ref_even"><td class="ref_ins">.</td><td>print byte at data pointer</td></tr>
 780         <tr class="ref_odd" ><td class="ref_ins">,</td><td>accept one byte of input</td></tr>
 781         <tr class="ref_even"><td class="ref_ins">*</td><td>set breakpoint</td></tr>
 782 </table>
 783
 784 <div id="memory_banner">MEMORY</div>
 785 <div id="ram_disp"></div>
 786 <div id="output_banner">OUTPUT</div>
 787 <div id="output">
 788 <textarea name=code id=output_disp rows="10" cols="38" disabled ></textarea>
 789 </div>
 790 <div id="docs">
 791         <div id="docs_top_banner">
 792                 Turing Tarpit Simulator Documentation&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 793                 <button id="docs_mnu_btn" onClick="docs_select('main');"><img src="http://opentextbook.info/icons/16x16/house.png">Main Menu</button>
 794                 <div id="docs_close_btn" onClick="hide_docs();"><img src="http://opentextbook.info/icons/16x16/cross.png"></div></div>
 795
 796         <div id="docs_content"></div>
 797 </div>
 798
 799 <div id="docs_main" class="docs_hidden">
 800                 <div id="docs_link" onClick="docs_select('basic');">Basic Operation</div>
 801                 <div id="docs_link" onClick="docs_select('features');">Features and Hints</div>
 802                 <div id="docs_link" onClick="docs_select('examples');">Example Code 1</div>
 803                 <div id="docs_link" onClick="docs_select('examples2');">Example Code 2</div>
 804                 <div id="docs_link" onClick="docs_select('ascii');">ASCII Chart</div>
 805 </div>
 806
 807 <div id="docs_basic" class="docs_hidden">
 808
 809 <b>Basic Operation</b>
 810
 811 <p>This Turing Tarpit is an abstract machine or a theoretical model of computer hardware.  The machine has 64 bytes of memory (RAM) and an almost unlimited amount of program storage (ROM). The instruction set is very simple. A user can program the tool by performing one of seven operations:
 812
 813 <p>The <b>'>'</b> and <b>'<'</b> symbols modify the Data Pointer to point to a new location in the Memory. It is possible to set the Data Pointer to a byte outside the machine's Memory. This does not cause an error. If you attempt to modify the memory at this location, the computer will crash and reboot with a SEGFAULT error.
 814
 815 <p>The <b>'+'</b> and <b>'-'</b> symbols allow the user to increment and decrement the Memory at the Data Pointer. Only one byte of Memory can be modified at any time. The byte of memory has a minimum and maximum value. When you exceed this value, the byte wraps around to zero.
 816
 817 <p>Another instruction <b>'.'</b> prints the contents of the byte at the Data Pointer. These numerical values listed in the Memory are converted into ASCII and printed as characters in the OUTPUT. A small chart of common ASCII values can be found in this documentation.
 818
 819 <p>The computer can interactively request data from the user with the <b>','</b> instruction. This opens up a dialog to request one byte of data from the user.
 820
 821 <p>An additional instruction <b>'*'</b> halts the execution of the program to allow the user to examine the machine at that point.  This is known as a BREAKPOINT. These breakpoints can be toggled on and off as well as automatically deleted from the code with the user interface below the INPUT.
 822
 823 <p>You can execute the program one step at a time or run the program at full speed until it needs user input or halts. Both methods are useful during development.
 824
 825 <p>More documentation is included in this manual. One section is dedicated to Features and Hints that will aid you in getting the most of this tool.  Another section is devoted to working code examples that provide a tutorial on how to best make use of the language.
 826
 827 </div>
 828
 829 <div id="docs_features" class="docs_hidden">
 830
 831 <b>Features and Hints</b>
 832
 833 <p>All characters outside the Instruction Set are considered comments and will be skipped over during runtime.
 834
 835 <p>While program executes, the Input cursor is moved over the current instruction.
 836
 837 <p>User can change the address of the Data Pointer and Instruction Pointer at any time.
 838 Memory and pointers that have been modified are highlighted in yellow until the next step.
 839
 840 <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.
 841
 842 <p>The Instruction Pointer can point to a location range of 1 to the number of characters in the input.
 843
 844 <p>Restarting the machine will reset all Memory, Data and Instruction Pointers to zero.
 845
 846 <p>The output of the program cannot be edited.
 847
 848 <p>A user can add a break instruction in the code using an asterisk <b>'*'</b>. 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.
 849
 850 <p>In this version the programs you type in are not saved to your computer.  This must be done as a manual operation.
 851
 852 <p>As this program is reliant on the speed and efficiency of your browser's JavaScript implementation some computers will be able to execute programs faster than others.
 853
 854 <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).
 855
 856 <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.
 857
 858 <p>No server interaction or outside service is needed for this program to operate.
 859 </div>
 860
 861
 862
 863
 864
 865 <div id="docs_examples" class="docs_hidden">
 866 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.
 867
 868 <p><button id="docs_try" onClick="docs_try('docs_example_clear_btye');"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Clear Byte:</b>
 869 Sets value at current Data Pointer to Zero.
 870 <div class=docs_code_ex>
 871 [-]
 872 </div>
 873 <p><button id="docs_try" onClick="docs_try('bad example');"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Clear Previous Cells:</b>
 874 Sets value of all previous bytes including current byte to Zero.
 875 <div class=docs_code_ex>
 876 [[-]<]
 877 </div>
 878 <p><button id="docs_try" onClick="docs_try();"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Rewind:</b>
 879 Goes back to byte Zero.
 880 <div class=docs_code_ex>
 881 [<]>
 882 </div>
 883 <p><button id="docs_try" onClick="docs_try();"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Fast-forward:</b>
 884 Increments the data pointer until a 0 is found then decrements if until the current cell is non-zero.
 885 <div class=docs_code_ex>
 886 [>]<
 887 </div>
 888 <p><button id="docs_try" onClick="docs_try();"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Simple Loop:</b>
 889 Accepts input from the user and echos it to the screen, similar to the UNIX cat program.
 890 <div class=docs_code_ex>
 891  ,[.,]
 892 </div>
 893 <p><button id="docs_try" onClick="docs_try();"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Moving the Data Pointer:</b>
 894 Accepts input from the user and saves all input in the memory for future use.
 895 <div class=docs_code_ex>
 896  >,[.>,]
 897 </div>
 898 </div>
 899
 900
 901
 902
 903
 904 <div id="docs_examples2" class="docs_hidden">
 905 <p><button id="docs_try" onClick="docs_try();"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Add Two Bytes:</b>
 906 Adds current location to the next location and leaves behind a Zero for the first value.
 907 <div class=docs_code_ex>
 908 [->+<]
 909 </div>
 910 <p><button id="docs_try" onClick="docs_try();"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Lower To Upper:</b>
 911 Accepts lower case input from the user and makes it uppercase. Stops when user presses the enter key.
 912 <div class=docs_code_ex>
 913 ,----------[----------------------.,----------]
 914 </div>
 915 <p><button id="docs_try" onClick="docs_try();"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Copy Value:</b>
 916 Copy value of byte Zero to byte One.
 917 <div class=docs_code_ex>
 918 >[-]>[-]<<[->+>+<<]>>[-<<+>>]<<
 919 </div>
 920 <p><button id="docs_try" onClick="docs_try();"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Seek:</b>
 921 Move Data Pointer forward until it lands on a byte with a value of 1, preserving all bytes it passes.
 922 <div class=docs_code_ex>
 923 -[+>-]+
 924 </div>
 925 <p><button id="docs_try" onClick="docs_try();"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Single Digit Add:</b>
 926 Adds two single digit numbers and display result. Works on one-digit results only.
 927 <div class=docs_code_ex>
 928 ,>++++++[<-------->-],[<+>-]<.
 929 </div>
 930 <p><button id="docs_try" onClick="docs_try();"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Single Digit Multiplication:</b>
 931 Multiply two single digit numbers and display result. Works on one-digit results only.
 932 <div class=docs_code_ex>
 933  ,>,>++++++++[<------<------>>-]
 934  <<[>[>+>+<<-]>>[<<+>>-]<<<-]
 935  >>>++++++[<++++++++>-]<.>.
 936 </div>
 937 <p><button id="docs_try" onClick="docs_try();"><img src="http://opentextbook.info/icons/16x16/bricks.png">Try</button><b>Single Digit Division:</b>
 938 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.
 939 <div class=docs_code_ex>
 940 ,>,>++++++[-<--------<-------->>]<<[>[->+>+<<]>[-<<-[>]>>>[<[>>>-<<<[-]]>>]<<]>>>+<<[-<<+>>]<<<]>[-]>>>>[-<<<<<+>>>>>]<<<<++++++[-<++++++++>]<.
 941 </div>
 942 </div>
 943
 944
 945
 946
 947
 948 <div id="docs_example_clear_btye" class="docs_hidden">
 949
 950 This is an example of clearing a byte
 951
 952 update first byte to higher number
 953 ++++++
 954
 955 set this byte to zero regardless of current value
 956 [-]
 957
 958 </div>
 959
 960 <div id="docs_ascii" class="docs_hidden">
 961
 962 <table id="ascii" width="900px">
 963 <caption><b>ASCII Chart</b></caption>
 964 <tr><th class="val_col"></th><th class="dat_col"></th><th class="val_col"></th><th class="dat_col"></th><th class="val_col"></th><th class="dat_col"></th><th class="val_col"></th><th class="dat_col"></th><th class="val_col"></th><th class="dat_col"></th><th class="val_col"></th><th class="dat_col"></th><th class="val_col"></th><th class="dat_col"></th><th class="val_col"></th><th class="dat_col"></th></tr>
 965
 966 <tr class="ref_even"><td>0</td><td class="ctrl">NUL</td><td>16</td><td class="ctrl">DLE</td><td>32</td><td class="ctrl">SP</td><td>48</td><td>0</td><td>64</td><td>@</td><td>80</td><td>P</td><td>96</td><td>`</td><td>112</td><td>p</td></tr>
 967
 968 <tr class="ref_odd"><td>1</td><td class="ctrl">SOH</td><td>17</td><td class="ctrl">DC1</td><td>33</td><td>!</td><td>49</td><td>1</td><td>65</td><td>A</td><td>81</td><td>Q</td><td>97</td><td>a</td><td>113</td><td>q</td></tr>
 969
 970 <tr class="ref_even"><td>2</td><td class="ctrl">STX</td><td>18</td><td class="ctrl">DC2</td><td>34</td><td>"</td><td>50</td><td>2</td><td>66</td><td>B</td><td>82</td><td>R</td><td>98</td><td>b</td><td>114</td><td>r</td></tr>
 971
 972 <tr class="ref_odd"><td>3</td><td class="ctrl">ETX</td><td>19</td><td class="ctrl">DC3</td><td>35</td><td>#</td><td>51</td><td>3</td><td>67</td><td>C</td><td>83</td><td>S</td><td>99</td><td>c</td><td>115</td><td>s</td></tr>
 973
 974 <tr class="ref_even"><td>4</td><td class="ctrl">EOT</td><td>20</td><td class="ctrl">DC4</td><td>36</td><td>$</td><td>52</td><td>4</td><td>68</td><td>D</td><td>84</td><td>T</td><td>100</td><td>d</td><td>116</td><td>t</td></tr>
 975
 976 <tr class="ref_odd"><td>5</td><td class="ctrl">ENQ</td><td>21</td><td class="ctrl">NAK</td><td>37</td><td>%</td><td>53</td><td>5</td><td>69</td><td>E</td><td>85</td><td>U</td><td>101</td><td>e</td><td>117</td><td>u</td></tr>
 977
 978 <tr class="ref_even"><td>6</td><td class="ctrl">ACK</td><td>22</td><td class="ctrl">SYN</td><td>38</td><td>&amp;</td><td>54</td><td>6</td><td>70</td><td>F</td><td>86</td><td>V</td><td>102</td><td>f</td><td>118</td><td>v</td></tr>
 979 <tr class="ref_odd"><td>7</td><td class="ctrl">BEL</td><td>23</td><td class="ctrl">ETB</td><td>39</td><td>'</td><td>55</td><td>7</td><td>71</td><td>G</td><td>87</td><td>W</td><td>103</td><td>g</td><td>119</td><td>w</td></tr>
 980
 981 <tr class="ref_even"><td>8</td><td class="ctrl">BS</td><td>24</td><td class="ctrl">CAN</td><td>40</td><td>(</td><td>56</td><td>8</td><td>72</td><td>H</td><td>88</td><td>X</td><td>104</td><td>h</td><td>120</td><td>x</td></tr>
 982
 983 <tr class="ref_odd"><td>9</td><td class="ctrl">HT</td><td>25</td><td class="ctrl">EM</td><td>41</td><td>)</td><td>57</td><td>9</td><td>73</td><td>I</td><td>89</td><td>Y</td><td>105</td><td>i</td><td>121</td><td>y</td></tr>
 984
 985 <tr class="ref_even"><td>10</td><td class="ctrl">LF</td><td>26</td><td class="ctrl">SUB</td><td>42</td><td>*</td><td>58</td><td>:</td><td>74</td><td>J</td><td>90</td><td>Z</td><td>106</td><td>j</td><td>122</td><td>z</td></tr>
 986
 987 <tr class="ref_odd"><td>11</td><td class="ctrl">VT</td><td>27</td><td class="ctrl">ESC</td><td>43</td><td>+</td><td>59</td><td>;</td><td>75</td><td>K</td><td>91</td><td>[</td><td>107</td><td>k</td><td>123</td><td>{</td></tr>
 988
 989 <tr class="ref_even"><td>12</td><td class="ctrl">FF</td><td>28</td><td class="ctrl">FS</td><td>44</td><td>,</td><td>60</td><td>&lt;</td><td>76</td><td>L</td><td>92</td><td>\</td><td>108</td><td>l</td><td>124</td><td>|</td></tr>
 990 <tr class="ref_odd"><td>13</td><td class="ctrl">CR</td><td>29</td><td class="ctrl">GS</td><td>45</td><td>-</td><td>61</td><td>=</td><td>77</td><td>M</td><td>93</td><td>]</td><td>109</td><td>m</td><td>125</td><td>}</td></tr>
 991
 992 <tr class="ref_even"><td>14</td><td class="ctrl">SO</td><td>30</td><td class="ctrl">RS</td><td>46</td><td>.</td><td>62</td><td>></td><td>78</td><td>N</td><td>94</td><td>^</td><td>110</td><td>n</td><td>126</td><td>~</td></tr>
 993
 994 <tr class="ref_odd"><td>15</td><td class="ctrl">SI</td><td>31</td><td class="ctrl">US</td><td>47</td><td>/</td><td>63</td><td>?</td><td>79</td><td>O</td><td>95</td><td>_</td><td>111</td><td>o</td><td>127</td><td class="ctrl">DEL</td></tr>
 995
 996 </table>
 997 </div>
 998
 999 </body>
1000 </html>
1001