Use JS array buffers for decodeDouble/Float. Faster, cleaner and less…

… buggy.
valderman · Jun 12, 2013 · 6d09e2b · 6d09e2b
1 parent 8a1a96a
commit 6d09e2b
Show file tree

Hide file tree

Showing 2 changed files with 30 additions and 45 deletions.
diff --git a/lib/Integer.js b/lib/Integer.js
@@ -715,17 +715,12 @@ var I_abs = function(self) {
 };
 
 var I_decodeDouble = function(x) {
-  if(isNaN(x)) {
-      return [1, 972, I_fromString('-6755399441055744')];
+  var dec = decodeDouble(x);
+  var mantissa = Integer.fromBits([dec[3], dec[2]]);
+  if(dec[1] < 0) {
+    mantissa = I_negate(mantissa);
   }
-  var sig = x > 0 ? 1 : -1;
-  if(!isFinite(x)) {
-      return [1, 972, I_fromNumber(sig) * I_fromString('4503599627370496')];
-  }
-  x = Math.abs(x);
-  var exp = log2(x)-52; // log2 is defined in rts.js
-  var man = x/Math.pow(2, exp);
-  return [1, exp, I_fromNumber(sig*man)];
+  return [1, dec[4], mantissa];
 }
 
 var I_toString = function(self) {

diff --git a/lib/rts.js b/lib/rts.js
@@ -115,47 +115,37 @@ function cosh (arg) {
     return (Math.exp(arg) + Math.exp(-arg)) / 2;
 }
 
-function log2(x) {
-    var high = 1024;
-    var low = -1024;
-    var i = 0;
-    var x2;
-    for(;;) {
-        x2 = Math.pow(2, i);
-        if(x2 <= (x >> 1)) {
-            low = i;
-            i += (high - i) >> 1;
-        } else if(x2 > x) {
-            high = i;
-            i += (low - i) >> 1;
-        } else {
-            return i;
-        }
-    }
-    return i;
-}
+// Scratch space for byte arrays.
+var rts_scratchBuf = new ArrayBuffer(8);
+var rts_scratchW32 = new Uint32Array(rts_scratchBuf);
+var rts_scratchFloat = new Float32Array(rts_scratchBuf);
+var rts_scratchDouble = new Float64Array(rts_scratchBuf);
 
 function decodeFloat(x) {
-    if(isNaN(x)) {
-        return [1, -6755399441055744, 972];
-    }
-    var sig = x > 0 ? 1 : -1;
-    if(!isFinite(x)) {
-        return [1, sig * 4503599627370496, 972];
+    rts_scratchFloat[0] = x;
+    var sign = x < 0 ? -1 : 1;
+    var exp = ((rts_scratchW32[0] >> 23) & 0xff) - 150;
+    var man = rts_scratchW32[0] & 0x7fffff;
+    if(exp === 0) {
+        ++exp;
+    } else {
+        man |= (1 << 23);
     }
-    x = Math.abs(x);
-    var exp = log2(x)-52;
-    var man = x/Math.pow(2, exp);
-    return [1, sig*man, exp];
+    return [1, sign*man, exp];
 }
 
 function decodeDouble(x) {
-    var decoded = decodeFloat(x);
-    var sign = decoded[1] < 0 ? -1 : 1;
-    var mantissa = decoded[1]*sign;
-    var manLow = mantissa % 0x100000000;
-    var manHigh = Math.floor(mantissa / 0x100000000);
-    return [1, sign, manHigh, manLow, decoded[2]];
+    rts_scratchDouble[0] = x;
+    var sign = x < 0 ? -1 : 1;
+    var manHigh = rts_scratchW32[1] & 0xfffff;
+    var manLow = rts_scratchW32[0];
+    var exp = ((rts_scratchW32[1] >> 20) & 0x7ff) - 1075;
+    if(exp === 0) {
+        ++exp;
+    } else {
+        manHigh |= (1 << 20);
+    }
+    return [1, sign, manHigh, manLow, exp];
 }
 
 function err(str) {