Fix DVI rounds towards zero

OttoAllmendinger · Aug 22, 2012 · 4a00f48 · 4a00f48
1 parent f14b336
commit 4a00f48
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Showing 2 changed files with 17 additions and 8 deletions.
diff --git a/lib/cpu.js b/lib/cpu.js
@@ -22,6 +22,14 @@ root.getSigned = function(word) {
     return word-sign;
 };
 
+var roundTowardsZero = function (number) {
+    if (number > 0) {
+        return Math.floor(number);
+    } else {
+        return Math.ceil(number);
+    }
+};
+
 var opcodes = [
     //assembler directives
     {id: 'DAT', cost: 0, args: Infinity},
@@ -346,7 +354,8 @@ CPU.prototype = {
 	                    this.set('ex', 0x0000);
 	                } else {
 	                    this.set('ex', (root.getSigned(bVal) << 16) / root.getSigned(aVal));
-	                    this.set(insn.b, Math.floor(root.getSigned(bVal) / root.getSigned(aVal)));
+                            var quotient = root.getSigned(bVal) / root.getSigned(aVal);
+	                    this.set(insn.b, roundTowardsZero(quotient));
 	                }
 	                break;
 

diff --git a/test/cpu_test.js b/test/cpu_test.js
@@ -356,13 +356,13 @@ module.exports = {
         assert.equal(cpu.get("ex"), 0x4000);
     },
 
-    // 'DVI negative number by nonzero should round quotitient towards zero': function () {
-    //     // -0x7FFF / 2 == -0x3fff.8
-    //     var cpu = runOnCpu("SET a, 0x8001",
-    //                        "DVI a, 0x2");
-    //     assert.equal(cpu.get("a"), 0xc001);
-    //     assert.equal(cpu.get("ex"), 0x8000);
-    // },
+    'DVI negative number by nonzero should round quotitient towards zero': function () {
+        // -0x7FFF / 2 == -0x3fff.8
+        var cpu = runOnCpu("SET a, 0x8001",
+                           "DVI a, 0x2");
+        assert.equal(cpu.get("a"), 0xc001);
+        assert.equal(cpu.get("ex"), 0x8000);
+    },
 
     'DVI with no next word values should take three cycles to perform': function () {
         var cpu = runOnCpu("DVI a, 1");