buffer: improve {read,write}{U}Int* methods

Increase the performance and simplify the logic of Buffer#write{U}Int*
and Buffer#read{U}Int* methods by placing the byte manipulation code
directly inline.

Also improve the speed of buffer-write benchmarks by creating a new
call directly to each method by using Function() instead of calling by
buff[fn].

Signed-off-by: Trevor Norris <trev.norris@gmail.com>

Author: mouna-apperson

benchmark/buffers/buffer-read.js

@@ -20,9 +20,12 @@ function main(conf) {
   var fn = 'read' + conf.type;
 
   buff.writeDoubleLE(0, 0, noAssert);
+  var testFunction = new Function('buff', [
+    "for (var i = 0; i !== " + len + "; i++) {",
+    "  buff." + fn + "(0, " + JSON.stringify(noAssert) + ");",
+    "}"
+  ].join("\n"));
   bench.start();
-  for (var i = 0; i < len; i++) {
-    buff[fn](0, noAssert);
-  }
+  testFunction(buff);
   bench.end(len / 1e6);
 }

benchmark/buffers/buffer-write.js

@@ -15,9 +15,9 @@ var bench = common.createBenchmark(main, {
 const INT8   = 0x7f;
 const INT16  = 0x7fff;
 const INT32  = 0x7fffffff;
-const UINT8  = INT8 * 2;
-const UINT16 = INT16 * 2;
-const UINT32 = INT32 * 2;
+const UINT8  = (INT8 * 2) + 1;
+const UINT16 = (INT16 * 2) + 1;
+const UINT32 = INT32;
 
 var mod = {
   writeInt8: INT8,
@@ -47,17 +47,23 @@ function main(conf) {
 
 function benchInt(buff, fn, len, noAssert) {
   var m = mod[fn];
+  var testFunction = new Function('buff', [
+    "for (var i = 0; i !== " + len + "; i++) {",
+    "  buff." + fn + "(i & " + m + ", 0, " + JSON.stringify(noAssert) + ");",
+    "}"
+  ].join("\n"));
   bench.start();
-  for (var i = 0; i < len; i++) {
-    buff[fn](i % m, 0, noAssert);
-  }
+  testFunction(buff);
   bench.end(len / 1e6);
 }
 
 function benchFloat(buff, fn, len, noAssert) {
+  var testFunction = new Function('buff', [
+    "for (var i = 0; i !== " + len + "; i++) {",
+    "  buff." + fn + "(i, 0, " + JSON.stringify(noAssert) + ");",
+    "}"
+  ].join("\n"));
   bench.start();
-  for (var i = 0; i < len; i++) {
-    buff[fn](i * 0.1, 0, noAssert);
-  }
+  testFunction(buff);
   bench.end(len / 1e6);
 }

lib/buffer.js

@@ -434,113 +434,45 @@ Buffer.prototype.readUInt8 = function(offset, noAssert) {
 };
 
 
-function readUInt16(buffer, offset, isBigEndian) {
-  var val = 0;
-  if (isBigEndian) {
-    val = buffer[offset] << 8;
-    val |= buffer[offset + 1];
-  } else {
-    val = buffer[offset];
-    val |= buffer[offset + 1] << 8;
-  }
-  return val;
-}
-
-
 Buffer.prototype.readUInt16LE = function(offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkOffset(offset, 2, this.length);
-  return readUInt16(this, offset, false, noAssert);
+  return this[offset] | (this[offset + 1] << 8);
 };
 
 
 Buffer.prototype.readUInt16BE = function(offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkOffset(offset, 2, this.length);
-  return readUInt16(this, offset, true, noAssert);
+  return (this[offset] << 8) | this[offset + 1];
 };
 
 
-function readUInt32(buffer, offset, isBigEndian) {
-  var val = 0;
-  if (isBigEndian) {
-    val = buffer[offset + 1] << 16;
-    val |= buffer[offset + 2] << 8;
-    val |= buffer[offset + 3];
-    val = val + (buffer[offset] << 24 >>> 0);
-  } else {
-    val = buffer[offset + 2] << 16;
-    val |= buffer[offset + 1] << 8;
-    val |= buffer[offset];
-    val = val + (buffer[offset + 3] << 24 >>> 0);
-  }
-  return val;
-}
-
-
 Buffer.prototype.readUInt32LE = function(offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkOffset(offset, 4, this.length);
-  return readUInt32(this, offset, false);
+
+  return ((this[offset]) |
+      (this[offset + 1] << 8) |
+      (this[offset + 2] << 16)) +
+      (this[offset + 3] * 0x1000000);
 };
 
 
 Buffer.prototype.readUInt32BE = function(offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkOffset(offset, 4, this.length);
-  return readUInt32(this, offset, true);
-};
 
+  return (this[offset] * 0x1000000) +
+      ((this[offset + 1] << 16) |
+      (this[offset + 2] << 8)) |
+      (this[offset + 3]);
+};
 
-/*
- * Signed integer types, yay team! A reminder on how two's complement actually
- * works. The first bit is the signed bit, i.e. tells us whether or not the
- * number should be positive or negative. If the two's complement value is
- * positive, then we're done, as it's equivalent to the unsigned representation.
- *
- * Now if the number is positive, you're pretty much done, you can just leverage
- * the unsigned translations and return those. Unfortunately, negative numbers
- * aren't quite that straightforward.
- *
- * At first glance, one might be inclined to use the traditional formula to
- * translate binary numbers between the positive and negative values in two's
- * complement. (Though it doesn't quite work for the most negative value)
- * Mainly:
- *  - invert all the bits
- *  - add one to the result
- *
- * Of course, this doesn't quite work in Javascript. Take for example the value
- * of -128. This could be represented in 16 bits (big-endian) as 0xff80. But of
- * course, Javascript will do the following:
- *
- * > ~0xff80
- * -65409
- *
- * Whoh there, Javascript, that's not quite right. But wait, according to
- * Javascript that's perfectly correct. When Javascript ends up seeing the
- * constant 0xff80, it has no notion that it is actually a signed number. It
- * assumes that we've input the unsigned value 0xff80. Thus, when it does the
- * binary negation, it casts it into a signed value, (positive 0xff80). Then
- * when you perform binary negation on that, it turns it into a negative number.
- *
- * Instead, we're going to have to use the following general formula, that works
- * in a rather Javascript friendly way. I'm glad we don't support this kind of
- * weird numbering scheme in the kernel.
- *
- * (BIT-MAX - (unsigned)val + 1) * -1
- *
- * The astute observer, may think that this doesn't make sense for 8-bit numbers
- * (really it isn't necessary for them). However, when you get 16-bit numbers,
- * you do. Let's go back to our prior example and see how this will look:
- *
- * (0xffff - 0xff80 + 1) * -1
- * (0x007f + 1) * -1
- * (0x0080) * -1
- */
 
 Buffer.prototype.readInt8 = function(offset, noAssert) {
   offset = offset >>> 0;
@@ -551,47 +483,45 @@ Buffer.prototype.readInt8 = function(offset, noAssert) {
 };
 
 
-function readInt16(buffer, offset, isBigEndian) {
-  var val = readUInt16(buffer, offset, isBigEndian);
-  return !(val & 0x8000) ? val : (0xffff - val + 1) * -1;
-}
-
-
 Buffer.prototype.readInt16LE = function(offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkOffset(offset, 2, this.length);
-  return readInt16(this, offset, false);
+  var val = this[offset] | (this[offset + 1] << 8);
+  return (val & 0x8000) ? val | 0xFFFF0000 : val;
 };
 
 
 Buffer.prototype.readInt16BE = function(offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkOffset(offset, 2, this.length);
-  return readInt16(this, offset, true);
+  var val = this[offset + 1] | (this[offset] << 8);
+  return (val & 0x8000) ? val | 0xFFFF0000 : val;
 };
 
 
-function readInt32(buffer, offset, isBigEndian) {
-  var val = readUInt32(buffer, offset, isBigEndian);
-  return !(val & 0x80000000) ? val : (0xffffffff - val + 1) * -1;
-}
-
-
 Buffer.prototype.readInt32LE = function(offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkOffset(offset, 4, this.length);
-  return readInt32(this, offset, false);
+
+  return (this[offset]) |
+      (this[offset + 1] << 8) |
+      (this[offset + 2] << 16) |
+      (this[offset + 3] << 24);
 };
 
 
 Buffer.prototype.readInt32BE = function(offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkOffset(offset, 4, this.length);
-  return readInt32(this, offset, true);
+
+  return (this[offset] << 24) |
+      (this[offset + 1] << 16) |
+      (this[offset + 2] << 8) |
+      (this[offset + 3]);
 };
 
 
@@ -615,24 +545,14 @@ Buffer.prototype.writeUInt8 = function(value, offset, noAssert) {
 };
 
 
-function writeUInt16(buffer, value, offset, isBigEndian) {
-  if (isBigEndian) {
-    buffer[offset] = (value & 0xff00) >>> 8;
-    buffer[offset + 1] = value & 0x00ff;
-  } else {
-    buffer[offset + 1] = (value & 0xff00) >>> 8;
-    buffer[offset] = value & 0x00ff;
-  }
-  return offset + 2;
-}
-
-
 Buffer.prototype.writeUInt16LE = function(value, offset, noAssert) {
   value = +value;
   offset = offset >>> 0;
   if (!noAssert)
     checkInt(this, value, offset, 2, 0xffff, 0);
-  return writeUInt16(this, value, offset, false);
+  this[offset] = value;
+  this[offset + 1] = (value >>> 8);
+  return offset + 2;
 };
 
 
@@ -641,32 +561,22 @@ Buffer.prototype.writeUInt16BE = function(value, offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkInt(this, value, offset, 2, 0xffff, 0);
-  return writeUInt16(this, value, offset, true);
+  this[offset] = (value >>> 8);
+  this[offset + 1] = value;
+  return offset + 2;
 };
 
 
-function writeUInt32(buffer, value, offset, isBigEndian) {
-  if (isBigEndian) {
-    buffer[offset] = (value >>> 24) & 0xff;
-    buffer[offset + 1] = (value >>> 16) & 0xff;
-    buffer[offset + 2] = (value >>> 8) & 0xff;
-    buffer[offset + 3] = value & 0xff;
-  } else {
-    buffer[offset + 3] = (value >>> 24) & 0xff;
-    buffer[offset + 2] = (value >>> 16) & 0xff;
-    buffer[offset + 1] = (value >>> 8) & 0xff;
-    buffer[offset] = value & 0xff;
-  }
-  return offset + 4;
-}
-
-
 Buffer.prototype.writeUInt32LE = function(value, offset, noAssert) {
   value = +value;
   offset = offset >>> 0;
   if (!noAssert)
     checkInt(this, value, offset, 4, 0xffffffff, 0);
-  return writeUInt32(this, value, offset, false);
+  this[offset + 3] = (value >>> 24);
+  this[offset + 2] = (value >>> 16);
+  this[offset + 1] = (value >>> 8);
+  this[offset] = value;
+  return offset + 4;
 };
 
 
@@ -675,9 +585,14 @@ Buffer.prototype.writeUInt32BE = function(value, offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkInt(this, value, offset, 4, 0xffffffff, 0);
-  return writeUInt32(this, value, offset, true);
+  this[offset] = (value >>> 24);
+  this[offset + 1] = (value >>> 16);
+  this[offset + 2] = (value >>> 8);
+  this[offset + 3] = value;
+  return offset + 4;
 };
 
+
 Buffer.prototype.writeInt8 = function(value, offset, noAssert) {
   value = +value;
   offset = offset >>> 0;
@@ -693,7 +608,9 @@ Buffer.prototype.writeInt16LE = function(value, offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkInt(this, value, offset, 2, 0x7fff, -0x8000);
-  return writeUInt16(this, value, offset, false);
+  this[offset] = value;
+  this[offset + 1] = (value >>> 8);
+  return offset + 2;
 };
 
 
@@ -702,7 +619,9 @@ Buffer.prototype.writeInt16BE = function(value, offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkInt(this, value, offset, 2, 0x7fff, -0x8000);
-  return writeUInt16(this, value, offset, true);
+  this[offset] = (value >>> 8);
+  this[offset + 1] = value;
+  return offset + 2;
 };
 
 
@@ -711,7 +630,11 @@ Buffer.prototype.writeInt32LE = function(value, offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkInt(this, value, offset, 4, 0x7fffffff, -0x80000000);
-  return writeUInt32(this, value, offset, false);
+  this[offset] = value;
+  this[offset + 1] = (value >>> 8);
+  this[offset + 2] = (value >>> 16);
+  this[offset + 3] = (value >>> 24);
+  return offset + 4;
 };
 
 
@@ -720,5 +643,9 @@ Buffer.prototype.writeInt32BE = function(value, offset, noAssert) {
   offset = offset >>> 0;
   if (!noAssert)
     checkInt(this, value, offset, 4, 0x7fffffff, -0x80000000);
-  return writeUInt32(this, value, offset, true);
+  this[offset] = (value >>> 24);
+  this[offset + 1] = (value >>> 16);
+  this[offset + 2] = (value >>> 8);
+  this[offset + 3] = value;
+  return offset + 4;
 };