Assorted 80386 and Debugger fixes

apps/c1p/all.xml

@@ -20,6 +20,6 @@
 		<item ref="/apps/c1p/BASIC/OSI/SAMPLE6.BAS">PRESIDENTS</item>
 		<item ref="/sites/www.osiweb.org/programs/basic/OsiBas/spacewar.bas">SPACEWAR</item>
 	</control>
-	<control type="button" binding="loadSerial">Download</control>
+	<control type="button" binding="loadSerial">Load</control>
 	<control type="file" binding="mountSerial" style="padding-left:16px"/>
 </serial>

apps/c1p/samples.xml

@@ -9,6 +9,6 @@
 		<item ref="/apps/c1p/BASIC/OSI/SAMPLE5.BAS">COUNTER</item>
 		<item ref="/apps/c1p/BASIC/OSI/SAMPLE6.BAS">PRESIDENTS</item>
 	</control>
-	<control type="button" binding="loadSerial">Download</control>
+	<control type="button" binding="loadSerial">Load</control>
 	<control type="file" binding="mountSerial" style="padding-left:16px"/>
 </serial>

devices/pc/bios/compaq/deskpro386/README.md

@@ -45,8 +45,8 @@ Similarly, [1989-04-14.json](1989-04-14/1989-04-14.json) was generated by first
 from the two 16Kb BIN files provided by [Al Kossow](http://www.vintage-computer.com/vcforum/member.php?2256-Al-Kossow):
 
 	cd 1989-04-14
-	filedump --file=private/109592-005.U11.bin --merge=private/109591-005.U13.bin --output=private/1989-04-14.rom --format=rom
+	filedump --file=static/109592-005.U11.bin --merge=static/109591-005.U13.bin --output=static/1989-04-14.rom --format=rom
-	filedump --file=private/1989-04-14.rom --output=1989-04-14.json
+	filedump --file=static/1989-04-14.rom --output=1989-04-14.json
 
 Dumping the ROMs
 ---

devices/pc/machine/5160/mda/256kb/fake188/debugger/machine.xml

@@ -23,7 +23,7 @@
 			<manifest ref="/apps/pc/1981/visicalc/manifest.xml" disk="*"/>
 			<manifest ref="/apps/pc/1982/esuite/manifest.xml" disk="*"/>
 		</control>
-		<control type="button" binding="loadDrive">Download</control>
+		<control type="button" binding="loadDrive">Load</control>
 		<control type="description" binding="descDisk" padleft="8px"/>
 		<control type="file" binding="mountDrive" padtop="8px"/>
 	</fdc>

devices/pc/machine/5160/mda/256kb/fake188/machine.xml

@@ -23,7 +23,7 @@
 			<manifest ref="/apps/pc/1981/visicalc/manifest.xml" disk="*"/>
 			<manifest ref="/apps/pc/1982/esuite/manifest.xml" disk="*"/>
 		</control>
-		<control type="button" binding="loadDrive" padright="8px">Download</control>
+		<control type="button" binding="loadDrive" padright="8px">Load</control>
 		<control type="description" binding="descDisk" padright="8px"/>
 		<control type="file" binding="mountDrive"/>
 	</fdc>

disks/pc/games/infocom/disks.xml

@@ -9,6 +9,6 @@
 		<manifest ref="/disks/pc/games/infocom/zork2/manifest.xml" disk="*"/>
 		<manifest ref="/disks/pc/games/infocom/zork3/manifest.xml" disk="*"/>
 	</control>
-	<control type="button" binding="loadDrive" padright="8px">Download</control>
+	<control type="button" binding="loadDrive" padright="8px">Load</control>
 	<control type="description" binding="descDisk" padright="8px"/>
 </fdc>

modules/pcjs/bin/x86gen.js

@@ -299,7 +299,7 @@ function genSIB(sib) {
             sMod = "((this.segData = this.segStack), " + sMod + ")";
         }
     }
-    var sBase = (base == 5? "(mod? " + sMod + " : this.getIPWord())" : "this.reg" + aBase[base]);
+    var sBase = (base == 5? "(mod? " + sMod + " : this.getIPAddr())" : "this.reg" + aBase[base]);
     if (index != 4) sBase += " + " + (scale? ("(this.reg" + aIndex[index] + " << " + scale + ")") : ("this.reg" + aIndex[index]));
     print("        return " + sBase + ";");
     print("    }" + (sib < 255? "," : ""));
@@ -473,7 +473,7 @@ function genMode(a, d, w, mrm, sGroup, sRO) {
                 nCycles = "this.cycleCounts.nEACyclesBase";             // 8086: 5
                 break;
             case 6:
-                sModAddr = "this.getIPWord()";
+                sModAddr = "this.getIPAddr()";
                 sModFunc = "D16";
                 nCycles = "this.cycleCounts.nEACyclesDisp";             // 8086: 6
                 break;
@@ -540,45 +540,45 @@ function genMode(a, d, w, mrm, sGroup, sRO) {
         case 2:
             switch (r_m) {
             case 0:
-                sModAddr = "this.regEBX + this.regESI + this.getIPWord()";
+                sModAddr = "this.regEBX + this.regESI + this.getIPAddr()";
                 sModFunc = "BXSID16";
                 nCycles = "this.cycleCounts.nEACyclesBaseIndexDisp";        // 8086: 11
                 break;
             case 1:
-                sModAddr = "this.regEBX + this.regEDI + this.getIPWord()";
+                sModAddr = "this.regEBX + this.regEDI + this.getIPAddr()";
                 sModFunc = "BXDID16";
                 nCycles = "this.cycleCounts.nEACyclesBaseIndexDispExtra";   // 8086: 12
                 break;
             case 2:
-                sModAddr = "this.regEBP + this.regESI + this.getIPWord()";
+                sModAddr = "this.regEBP + this.regESI + this.getIPAddr()";
                 sModFunc = "BPSID16";
                 sModRegSeg = "Stack";
                 nCycles = "this.cycleCounts.nEACyclesBaseIndexDispExtra";   // 8086: 12
                 break;
             case 3:
-                sModAddr = "this.regEBP + this.regEDI + this.getIPWord()";
+                sModAddr = "this.regEBP + this.regEDI + this.getIPAddr()";
                 sModFunc = "BPDID16";
                 sModRegSeg = "Stack";
                 nCycles = "this.cycleCounts.nEACyclesBaseIndexDisp";        // 8086: 11
                 break;
             case 4:
-                sModAddr = "this.regESI + this.getIPWord()";
+                sModAddr = "this.regESI + this.getIPAddr()";
                 sModFunc = "SID16";
                 nCycles = "this.cycleCounts.nEACyclesBaseDisp";             // 8086: 9
                 break;
             case 5:
-                sModAddr = "this.regEDI + this.getIPWord()";
+                sModAddr = "this.regEDI + this.getIPAddr()";
                 sModFunc = "DID16";
                 nCycles = "this.cycleCounts.nEACyclesBaseDisp";             // 8086: 9
                 break;
             case 6:
-                sModAddr = "this.regEBP + this.getIPWord()";
+                sModAddr = "this.regEBP + this.getIPAddr()";
                 sModFunc = "BPD16";
                 sModRegSeg = "Stack";
                 nCycles = "this.cycleCounts.nEACyclesBaseDisp";             // 8086: 9
                 break;
             case 7:
-                sModAddr = "this.regEBX + this.getIPWord()";
+                sModAddr = "this.regEBX + this.getIPAddr()";
                 sModFunc = "BXD16";
                 nCycles = "this.cycleCounts.nEACyclesBaseDisp";             // 8086: 9
                 break;
@@ -729,7 +729,7 @@ function genMode(a, d, w, mrm, sGroup, sRO) {
                 nCycles = "this.cycleCounts.nEACyclesBase";
                 break;
             case 5:
-                sModAddr = "this.getIPWord()";
+                sModAddr = "this.getIPAddr()";
                 sModFunc = "D32";
                 nCycles = "this.cycleCounts.nEACyclesDisp";
                 break;
@@ -799,43 +799,43 @@ function genMode(a, d, w, mrm, sGroup, sRO) {
         case 2:
             switch (r_m) {
             case 0:
-                sModAddr = "this.regEAX + this.getIPWord()";
+                sModAddr = "this.regEAX + this.getIPAddr()";
                 sModFunc = "EAXD32";
                 nCycles = "this.cycleCounts.nEACyclesBaseDisp";
                 break;
             case 1:
-                sModAddr = "this.regECX + this.getIPWord()";
+                sModAddr = "this.regECX + this.getIPAddr()";
                 sModFunc = "ECXD32";
                 nCycles = "this.cycleCounts.nEACyclesBaseDisp";
                 break;
             case 2:
-                sModAddr = "this.regEDX + this.getIPWord()";
+                sModAddr = "this.regEDX + this.getIPAddr()";
                 sModFunc = "EDXD32";
                 nCycles = "this.cycleCounts.nEACyclesBaseDisp";
                 break;
             case 3:
-                sModAddr = "this.regEBX + this.getIPWord()";
+                sModAddr = "this.regEBX + this.getIPAddr()";
                 sModFunc = "EBXD32";
                 nCycles = "this.cycleCounts.nEACyclesBaseDisp";
                 break;
             case 4:
-                sModAddr = "this.getSIBAddr(2) + this.getIPWord()";
+                sModAddr = "this.getSIBAddr(2) + this.getIPAddr()";
                 sModFunc = "SIBD32";
                 nCycles = "this.cycleCounts.nEACyclesBaseDisp";
                 break;
             case 5:
-                sModAddr = "this.regEBP + this.getIPWord()";
+                sModAddr = "this.regEBP + this.getIPAddr()";
                 sModFunc = "EBPD32";
                 sModRegSeg = "Stack";
                 nCycles = "this.cycleCounts.nEACyclesBaseDisp";
                 break;
             case 6:
-                sModAddr = "this.regESI + this.getIPWord()";
+                sModAddr = "this.regESI + this.getIPAddr()";
                 sModFunc = "ESID32";
                 nCycles = "this.cycleCounts.nEACyclesBaseDisp";
                 break;
             case 7:
-                sModAddr = "this.regEDI + this.getIPWord()";
+                sModAddr = "this.regEDI + this.getIPAddr()";
                 sModFunc = "EDID32";
                 nCycles = "this.cycleCounts.nEACyclesBaseDisp";
                 break;

modules/pcjs/lib/debugger.js

@@ -1373,9 +1373,28 @@ if (DEBUGGER) {
      */
     Debugger.prototype.newAddr = function(off, seg, addr, fData32, fAddr32)
     {
+        if (fData32 === undefined) fData32 = (this.cpu.segCS.dataSize == 4);
+        if (fAddr32 === undefined) fAddr32 = (this.cpu.segCS.addrSize == 4);
         return [off, seg, addr, false, fData32, fAddr32];
     };
 
+    /**
+     * checkLimit(aAddr)
+     *
+     * @this {Debugger}
+     * @param {Array} aAddr containing [off, seg, addr]
+     */
+    Debugger.prototype.checkLimit = function(aAddr)
+    {
+        if (aAddr[1] != null) {
+            var limit = this.getSegment(aAddr[1]).limit;
+            if (aAddr[0] > limit) {
+                aAddr[0] = 0;
+                aAddr[2] = null;
+            }
+        }
+    };
+
     /**
      * incAddr(aAddr, inc)
      *
@@ -1391,11 +1410,7 @@ if (DEBUGGER) {
         }
         if (aAddr[1] != null) {
             aAddr[0] += inc;
-            var limit = this.getSegment(aAddr[1]).limit;
+            this.checkLimit(aAddr);
-            if (aAddr[0] > limit) {
-                aAddr[0] = 0;
-                aAddr[2] = null;
-            }
         }
     };
 
@@ -1408,22 +1423,22 @@ if (DEBUGGER) {
      */
     Debugger.prototype.hexAddr = function(aAddr)
     {
-        return aAddr[1] == null? ("%" + str.toHex(aAddr[2])) : this.hexOffset(aAddr[0], aAddr[1], aAddr[4]);
+        return aAddr[1] == null? ("%" + str.toHex(aAddr[2])) : this.hexOffset(aAddr[0], aAddr[1], aAddr[5]);
     };
 
     /**
-     * hexOffset(off, sel)
+     * hexOffset(off, sel, fAddr32)
      *
      * @this {Debugger}
      * @param {number} off
      * @param {number} [sel]
-     * @param {boolean} [fData32] is true if 32-bit OPERAND size in effect
+     * @param {boolean} [fAddr32] is true to force 32-bit ADDRESS size
      * @return {string} the hex representation of off (or sel:off)
      */
-    Debugger.prototype.hexOffset = function(off, sel, fData32)
+    Debugger.prototype.hexOffset = function(off, sel, fAddr32)
     {
         if (sel !== undefined) {
-            return str.toHex(sel, 4) + ":" + str.toHex(off, fData32? 8 : 4);
+            return str.toHex(sel, 4) + ":" + str.toHex(off, (off & (0xffff0000|0)) || fAddr32? 8 : 4);
         }
         return str.toHex(off);
     };
@@ -2958,14 +2973,16 @@ if (DEBUGGER) {
      */
     Debugger.prototype.getInstruction = function(aAddr, sComment, nSequence)
     {
-        var aAddrIns = this.newAddr(aAddr[0], aAddr[1], aAddr[2], this.cpu.segCS.addrSize == 4);
+        var aAddrIns = this.newAddr(aAddr[0], aAddr[1], aAddr[2]);
 
         var bOpcode = this.getByte(aAddr, 1);
 
         /*
-         * Incorporate the following prefixes into the current instruction's byte stream
+         * Incorporate the following prefixes into the current instruction byte stream.
+         * TODO: Determine the actual effect of multiple OS (and/or multiple AS) prefixes.
          */
-        if (bOpcode == X86.OPCODE.OS || bOpcode == X86.OPCODE.AS) {
+        var cMax = 2;           // let's make sure unfortunate memory contents don't screw us
+        while ((bOpcode == X86.OPCODE.OS || bOpcode == X86.OPCODE.AS) && cMax--) {
             if (bOpcode == X86.OPCODE.OS) {
                 aAddr[4] = !aAddr[4];
             } else {
@@ -3134,7 +3151,7 @@ if (DEBUGGER) {
                 sOperand = str.toHex(this.getShort(aAddr, 2), 4);
                 break;
             case Debugger.TYPE_FARP:
-                sOperand = this.hexAddr(this.newAddr(this.getWord(aAddr, 2), this.getShort(aAddr, 2), null, aAddr[4]));
+                sOperand = this.hexAddr(this.newAddr(this.getWord(aAddr, 2), this.getShort(aAddr, 2), null, aAddr[4], aAddr[5]));
                 break;
             default:
                 sOperand = "imm(" + str.toHexWord(type) + ")";
@@ -3550,7 +3567,9 @@ if (DEBUGGER) {
                 addr = null;
             }
         }
-        return [off, seg, addr];
+        var aAddr = [off, seg, addr];
+        this.checkLimit(aAddr);
+        return aAddr;
     };
 
     /**
@@ -4021,14 +4040,13 @@ if (DEBUGGER) {
      * because we always display whole lines.  If sLen is omitted/undefined, then we default to 8 lines, regardless
      * whether dumping bytes or words.
      *
-     * Also, unlike sAddr, sLen is interpreted as a decimal number, unless a radix specifier in included (eg, "0x100").
+     * Also, unlike sAddr, sLen is interpreted as a decimal number, unless a radix specifier is included (eg, "0x100");
-     *
+     * sLen also supports the DEBUG.COM-style syntax of a preceding "l" (eg, "l16").
-     * And finally, sLen also support the DEBUG.COM-style syntax of a preceding "l" (eg, "l16").
      *
      * @this {Debugger}
      * @param {string} sCmd
      * @param {string|undefined} sAddr
-     * @param {string|undefined} sLen (if present, it can be preceded by an "l", which we simply ignore; this is purely for historical reasons)
+     * @param {string|undefined} sLen (if present, it can be preceded by an "l", which we simply ignore)
      */
     Debugger.prototype.doDump = function(sCmd, sAddr, sLen)
     {
@@ -4046,6 +4064,7 @@ if (DEBUGGER) {
             this.println("\tdb [a] [#]    dump # bytes at address a");
             if (BACKTRACK) this.println("\tdi [a]        dump backtrack info at address a");
             this.println("\tdw [a] [#]    dump # words at address a");
+            this.println("\tdd [a] [#]    dump # dwords at address a");
             if (sDumpers.length) this.println("dump extensions:\n\t" + sDumpers);
             return;
         }
@@ -4085,32 +4104,30 @@ if (DEBUGGER) {
         }
         else {
             var cLines = 0;
-            var fWords = (sCmd == "dw");
+            var cBytes = (sCmd == "dd"? 4 : (sCmd == "dw"? 2 : 1));
-            if (sLen !== undefined) {
+            var cNumbers = (16 / cBytes)|0;
+            if (sLen) {
                 if (sLen.charAt(0) == "l") sLen = sLen.substr(1);
                 cLines = +sLen;
-                if (cLines) cLines = fWords? ((cLines + 7) >> 3) : ((cLines + 15) >> 4);
+                if (cLines) cLines = ((cLines + cNumbers - 1) / cNumbers)|0;
             }
             if (!cLines) cLines = 8;
             for (var iLine = 0; iLine < cLines; iLine++) {
-                var bPrev = 0;
+                var data = 0, iByte = 0;
-                var sBytes = "", sChars = "";
+                var sData = "", sChars = "";
                 sAddr = this.hexAddr(aAddr);
                 for (var i = 0; i < 16; i++) {
                     var b = this.getByte(aAddr, 1);
-                    if (fWords) {
+                    data |= (b << (iByte++ << 3));
-                        if (i & 0x1) {
+                    if (iByte == cBytes) {
-                            sBytes += str.toHex(bPrev | (b << 8), 4) + (i == 7? " - " : "  ");
+                        sData += str.toHex(data, cBytes * 2);
-                        }
+                        sData += (cBytes == 1? (i == 7? '-' : ' ') : "  ");
-                    }
+                        data = iByte = 0;
-                    else {
-                        sBytes += str.toHex(b, 2) + (i == 7? "-" : " ");
                     }
                     sChars += (b >= 32 && b < 128? String.fromCharCode(b) : ".");
-                    bPrev = b;
                 }
                 if (sDump) sDump += "\n";
-                sDump += sAddr + "  " + sBytes + " " + sChars;
+                sDump += sAddr + "  " + sData + " " + sChars;
             }
         }
         if (sDump) this.println(sDump);

modules/pcjs/lib/ram.js

@@ -289,7 +289,7 @@ function CompaqController(ram)
     this.aBlocksDst = null;
 }
 
-CompaqController.ADDR       = 0x80C00000;
+CompaqController.ADDR       =(0x80C00000|0);
 CompaqController.MAP_SRC    = 0x00FE0000;
 CompaqController.MAP_DST    = 0x000E0000;
 CompaqController.MAP_SIZE   = 0x00020000;

modules/pcjs/lib/x86.js

@@ -173,7 +173,7 @@ var X86 = {
     },
     LADDR: {                // linear address
         PDE: {              // index of page directory entry
-            MASK:   0xffc00000,
+            MASK:   0xffc00000|0,
             SHIFT:  20      // (addr & DIR.MASK) >>> DIR.SHIFT yields a page directory offset (ie, index * 4)
         },
         PTE: {              // index of page table entry
@@ -183,7 +183,7 @@ var X86 = {
         OFFSET:     0x00000fff
     },
     PTE: {
-        FRAME:      0xfffff000,
+        FRAME:      0xfffff000|0,
         DIRTY:      0x00000040,         // page has been modified
         ACCESSED:   0x00000020,         // page has been accessed
         USER:       0x00000004,         // set for user level (CPL 3), clear for supervisor level (CPL 0-2)

modules/pcjs/lib/x86cpu.js

@@ -2522,7 +2522,7 @@ X86CPU.prototype.setBinding = function(sHTMLType, sBinding, control)
  * @param {number} addr is a physical (non-segmented) address
  * @return {number} byte (8-bit) value at that address
  */
-X86CPU.prototype.getByte = function(addr)
+X86CPU.prototype.getByte = function getByte(addr)
 {
     if (BACKTRACK) this.backTrack.btiMemLo = this.bus.readBackTrack(addr);
     return this.aMemBlocks[(addr & this.busMask) >>> this.blockShift].readByte(addr & this.blockLimit, addr);
@@ -2535,7 +2535,7 @@ X86CPU.prototype.getByte = function(addr)
  * @param {number} addr is a physical (non-segmented) address
  * @return {number} word (16-bit) value at that address
  */
-X86CPU.prototype.getShort = function(addr)
+X86CPU.prototype.getShort = function getShort(addr)
 {
     var off = addr & this.blockLimit;
     var iBlock = (addr & this.busMask) >>> this.blockShift;
@@ -2562,7 +2562,7 @@ X86CPU.prototype.getShort = function(addr)
  * @param {number} addr is a physical (non-segmented) address
  * @return {number} long (32-bit) value at that address
  */
-X86CPU.prototype.getLong = function(addr)
+X86CPU.prototype.getLong = function getLong(addr)
 {
     var off = addr & this.blockLimit;
     var iBlock = (addr & this.busMask) >>> this.blockShift;
@@ -2584,7 +2584,7 @@ X86CPU.prototype.getLong = function(addr)
  * @param {number} addr is a physical (non-segmented) address
  * @param {number} b is the byte (8-bit) value to write (which we truncate to 8 bits; required by opSTOSb)
  */
-X86CPU.prototype.setByte = function(addr, b)
+X86CPU.prototype.setByte = function setByte(addr, b)
 {
     if (BACKTRACK) this.bus.writeBackTrack(addr, this.backTrack.btiMemLo);
     this.aMemBlocks[(addr & this.busMask) >>> this.blockShift].writeByte(addr & this.blockLimit, b & 0xff, addr);
@@ -2597,7 +2597,7 @@ X86CPU.prototype.setByte = function(addr, b)
  * @param {number} addr is a physical (non-segmented) address
  * @param {number} w is the word (16-bit) value to write (which we truncate to 16 bits to be safe)
  */
-X86CPU.prototype.setShort = function(addr, w)
+X86CPU.prototype.setShort = function setShort(addr, w)
 {
     var off = addr & this.blockLimit;
     var iBlock = (addr & this.busMask) >>> this.blockShift;
@@ -2626,7 +2626,7 @@ X86CPU.prototype.setShort = function(addr, w)
  * @param {number} addr is a physical (non-segmented) address
  * @param {number} l is the long (32-bit) value to write
  */
-X86CPU.prototype.setLong = function(addr, l)
+X86CPU.prototype.setLong = function setLong(addr, l)
 {
     var off = addr & this.blockLimit;
     var iBlock = (addr & this.busMask) >>> this.blockShift;

modules/pcjs/lib/x86func.js

@@ -2629,7 +2629,7 @@ X86.fnSGDT = function SGDT(dst, src)
          *
          * This code is expecting SGDT on an 80286 to set the 6th "undefined" byte to 0xFF.
          */
-        var addr = this.addrGDT | (this.model == X86.MODEL_80286? 0xff000000 : 0);
+        var addr = this.addrGDT | (this.model == X86.MODEL_80286? (0xff000000|0) : 0);
         this.setLong(this.regEA + 2, addr);
         this.nStepCycles -= 11;
     }
@@ -2981,7 +2981,7 @@ X86.fnSIDT = function SIDT(dst, src)
          * As with SGDT, the 6th byte is technically "undefined" on an 80286, but we now set it to 0xFF, for the
          * same reasons discussed in SGDT (above).
          */
-        var addr = this.addrIDT | (this.model == X86.MODEL_80286? 0xff000000 : 0);
+        var addr = this.addrIDT | (this.model == X86.MODEL_80286? (0xff000000|0) : 0);
         this.setLong(this.regEA + 2, addr);
         this.nStepCycles -= 12;
     }

modules/pcjs/lib/x86seg.js

@@ -288,7 +288,11 @@ X86Seg.prototype.checkWriteReal = function checkWriteReal(off, cb, fSuppress)
  */
 X86Seg.prototype.checkReadProt = function checkReadProt(off, cb, fSuppress)
 {
-    if (off + cb - 1 <= this.limit) {
+    /*
+     * Since "off" could be a 32-bit value with the sign bit (bit 31) set, we must convert
+     * it to an unsigned value using ">>>"; limit was already converted at segment load time.
+     */
+    if ((off >>> 0) + cb - 1 <= this.limit) {
         return (this.base + off)|0;
     }
     return this.checkReadProtDisallowed(off, cb, fSuppress);
@@ -305,7 +309,11 @@ X86Seg.prototype.checkReadProt = function checkReadProt(off, cb, fSuppress)
  */
 X86Seg.prototype.checkReadProtDown = function checkReadProtDown(off, cb, fSuppress)
 {
-    if (off + cb - 1 > this.limit) {
+    /*
+     * Since "off" could be a 32-bit value with the sign bit (bit 31) set, we must convert
+     * it to an unsigned value using ">>>"; limit was already converted at segment load time.
+     */
+    if ((off >>> 0) + cb - 1 > this.limit) {
         return (this.base + off)|0;
     }
     return this.checkReadProtDisallowed(off, cb, fSuppress);
@@ -339,7 +347,11 @@ X86Seg.prototype.checkReadProtDisallowed = function checkReadProtDisallowed(off,
  */
 X86Seg.prototype.checkWriteProt = function checkWriteProt(off, cb, fSuppress)
 {
-    if (off + cb - 1 <= this.limit) {
+    /*
+     * Since "off" could be a 32-bit value with the sign bit (bit 31) set, we must convert
+     * it to an unsigned value using ">>>"; limit was already converted at segment load time.
+     */
+    if ((off >>> 0) + cb - 1 <= this.limit) {
         return (this.base + off)|0;
     }
     return this.checkWriteProtDisallowed(off, cb, fSuppress);
@@ -356,7 +368,11 @@ X86Seg.prototype.checkWriteProt = function checkWriteProt(off, cb, fSuppress)
  */
 X86Seg.prototype.checkWriteProtDown = function checkWriteProtDown(off, cb, fSuppress)
 {
-    if (off + cb - 1 > this.limit) {
+    /*
+     * Since "off" could be a 32-bit value with the sign bit (bit 31) set, we must convert
+     * it to an unsigned value using ">>>"; limit was already converted at segment load time.
+     */
+    if ((off >>> 0) + cb - 1 > this.limit) {
         return (this.base + off)|0;
     }
     return this.checkWriteProtDisallowed(off, cb, fSuppress);
@@ -748,7 +764,11 @@ X86Seg.prototype.loadDesc8 = function(addrDesc, sel, fSuppress)
         }
         this.sel = sel;
         this.base = base;
-        this.limit = limit;
+        /*
+         * Since limit could be a 32-bit value with the sign bit (bit 31) set, we convert
+         * it to an unsigned value now, using ">>>", so that the limit checks won't have to.
+         */
+        this.limit = (limit >>> 0);
         this.acc = acc;
         this.type = type;
         this.ext = ext;

pubs/pc/programming/Graphics_for_the_IBM_PC/demos/basic.xml

@@ -10,7 +10,7 @@
 		<manifest ref="/apps/pc/1981/visicalc/manifest.xml" disk="*"/>
 		<disk path="/api/v1/dump?dir=/pubs/pc/programming/Graphics_for_the_IBM_PC/programs">BASIC Programs</disk>
 	</control>
-	<control type="button" binding="loadDrive" padright="8px">Download</control>
+	<control type="button" binding="loadDrive" padright="8px">Load</control>
 	<control type="description" binding="descDisk" padright="8px"/>
 	<control type="file" binding="mountDrive"/>
 </fdc>