From c431e5dde84dc2c88e1b8b8566c7e700b6868f70 Mon Sep 17 00:00:00 2001
From: Jeff Parsons <Jeff@pcjs.org>
Date: Thu, 14 May 2015 13:11:46 -0700
Subject: [PATCH] Future-proof ADDR_INVALID checks by using strict [in]equality

---
 modules/pcjs/lib/debugger.js |  7 +++----
 modules/pcjs/lib/x86func.js  | 12 ++++++------
 modules/pcjs/lib/x86seg.js   |  2 +-
 3 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/modules/pcjs/lib/debugger.js b/modules/pcjs/lib/debugger.js
index 9522674ec..f0b53b552 100644
--- a/modules/pcjs/lib/debugger.js
+++ b/modules/pcjs/lib/debugger.js
@@ -410,9 +410,8 @@ if (DEBUGGER) {
     Debugger.TYPE_OTHER     = 0xF000;   // "other" field
 
     /*
-     * TYPE_SIZE values.  Note that some of the values (eg, TYPE_WORDIB
-     * and TYPE_WORDIW) imply the presence of a third operand, for those
-     * weird cases....
+     * TYPE_SIZE values.  Some of the values (eg, TYPE_WORDIB and TYPE_WORDIW)
+     * imply the presence of a third operand, for those weird cases....
      */
     Debugger.TYPE_NONE      = 0x0000;   //     (all other TYPE fields ignored)
     Debugger.TYPE_BYTE      = 0x0001;   // (b) byte, regardless of operand size
@@ -428,7 +427,7 @@ if (DEBUGGER) {
     Debugger.TYPE_PREFIX    = 0x000F;   //     (treat similarly to TYPE_NONE)
 
     /*
-     * TYPE_MODE values.  Note that order is somewhat important, as all values implying
+     * TYPE_MODE values.  Order is somewhat important, as all values implying
      * the presence of a ModRM byte are assumed to be >= TYPE_MODRM.
      */
     Debugger.TYPE_IMM       = 0x0000;   // (I) immediate data
diff --git a/modules/pcjs/lib/x86func.js b/modules/pcjs/lib/x86func.js
index a75899445..e213db598 100644
--- a/modules/pcjs/lib/x86func.js
+++ b/modules/pcjs/lib/x86func.js
@@ -1216,7 +1216,7 @@ X86.fnINT = function INT(nIDT, nError, nCycles)
     var oldCS = this.getCS();
     var oldIP = this.getIP();
     var addr = this.segCS.loadIDT(nIDT);
-    if (addr != X86.ADDR_INVALID) {
+    if (addr !== X86.ADDR_INVALID) {
         this.regLIP = addr;
         if (PREFETCH) this.flushPrefetch(this.regLIP);
         this.pushWord(oldPS);
@@ -1311,7 +1311,7 @@ X86.fnLAR = function LAR(dst, src)
      * TODO: This instruction's 80286 documentation does not discuss conforming code segments; determine
      * if we need a special check for them.
      */
-    if (this.segVER.load(src, true) != X86.ADDR_INVALID) {
+    if (this.segVER.load(src, true) !== X86.ADDR_INVALID) {
         if (this.segVER.dpl >= this.segCS.cpl && this.segVER.dpl >= (src & X86.SEL.RPL)) {
             this.setZF();
             return this.segVER.acc & X86.DESC.ACC.MASK;
@@ -1600,7 +1600,7 @@ X86.fnLSL = function LSL(dst, src)
      * TODO: LSL is explicitly documented as ALSO requiring a non-null selector, so we check X86.SEL.MASK;
      * are there any other instructions that were, um, less explicit but also require a non-null selector?
      */
-    if ((src & X86.SEL.MASK) && this.segVER.load(src, true) != X86.ADDR_INVALID) {
+    if ((src & X86.SEL.MASK) && this.segVER.load(src, true) !== X86.ADDR_INVALID) {
         var fConforming = ((this.segVER.acc & X86.DESC.ACC.TYPE.CODE_CONFORMING) == X86.DESC.ACC.TYPE.CODE_CONFORMING);
         if ((fConforming || this.segVER.dpl >= this.segCS.cpl) && this.segVER.dpl >= (src & X86.SEL.RPL)) {
             this.setZF();
@@ -1643,7 +1643,7 @@ X86.fnLSS = function LSS(dst, src)
 X86.fnLTR = function LTR(dst, src)
 {
     this.opFlags |= X86.OPFLAG.NOWRITE;
-    if (this.segTSS.load(dst) != X86.ADDR_INVALID) {
+    if (this.segTSS.load(dst) !== X86.ADDR_INVALID) {
         this.setShort(this.segTSS.addrDesc + X86.DESC.ACC.OFFSET, this.segTSS.acc |= X86.DESC.ACC.TYPE.LDT);
         this.segTSS.type = X86.DESC.ACC.TYPE.TSS_BUSY;
     }
@@ -3237,7 +3237,7 @@ X86.fnVERR = function VERR(dst, src)
      * descriptor table or the descriptor is not for a segment.
      */
     this.nStepCycles -= (14 + (this.regEA === X86.ADDR_INVALID? 0 : 2));
-    if (this.segVER.load(dst, true) != X86.ADDR_INVALID) {
+    if (this.segVER.load(dst, true) !== X86.ADDR_INVALID) {
         /*
          * Verify that this is a readable segment; that is, of these four combinations (code+readable,
          * code+nonreadable, data+writable, date+nonwritable), make sure we're not the second combination.
@@ -3279,7 +3279,7 @@ X86.fnVERW = function VERW(dst, src)
      * descriptor table or the descriptor is not for a segment.
      */
     this.nStepCycles -= (14 + (this.regEA === X86.ADDR_INVALID? 0 : 2));
-    if (this.segVER.load(dst, true) != X86.ADDR_INVALID) {
+    if (this.segVER.load(dst, true) !== X86.ADDR_INVALID) {
         /*
          * Verify that this is a writable data segment
          */
diff --git a/modules/pcjs/lib/x86seg.js b/modules/pcjs/lib/x86seg.js
index a38d4b4b9..1ac96eaf1 100644
--- a/modules/pcjs/lib/x86seg.js
+++ b/modules/pcjs/lib/x86seg.js
@@ -982,7 +982,7 @@ X86Seg.prototype.updateMode = function(fLoad, fProt)
              * hardware does not update it either.  In fact, I've seen code that uses the null GDT descriptor
              * for other purposes, on the assumption that that descriptor is completely unused.
              */
-            if ((this.sel & ~X86.SEL.RPL) && this.addrDesc != X86.ADDR_INVALID) {
+            if ((this.sel & ~X86.SEL.RPL) && this.addrDesc !== X86.ADDR_INVALID) {
                 var addrACC = this.addrDesc + X86.DESC.ACC.TYPE.OFFSET;
                 this.cpu.setByte(addrACC, this.cpu.getByte(addrACC) | (X86.DESC.ACC.TYPE.ACCESSED >> 8));
             }