buffer: add generic functions for (u)int ops
Add generic functions for (U)Int read/write operations on Buffers. These support up to and including 48 bit reads and writes. Include documentation and tests. Additional work done by Trevor Norris to include 40 and 48 bit write support. Because bitwise operations cannot be used on values greater than 32 bits, the operations have been replaced with mathematical calculations. Regardless, they are still faster than floating point operations. Reviewed-by: Trevor Norris <trev.norris@gmail.com>
This commit is contained in:
Yazhong Liu
Trevor Norris
parent
e9ca7b9d8d
commit
83d7d9e6d8
@ -180,6 +180,48 @@ The method will not write partial characters.
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len = buf.write('\u00bd + \u00bc = \u00be', 0);
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console.log(len + " bytes: " + buf.toString('utf8', 0, len));
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### buf.writeUIntLE(value, offset, byteLength[, noAssert])
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### buf.writeUIntBE(value, offset, byteLength[, noAssert])
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### buf.writeIntLE(value, offset, byteLength[, noAssert])
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### buf.writeIntBE(value, offset, byteLength[, noAssert])
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* `value` {Number} Bytes to be written to buffer
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* `offset` {Number} `0 <= offset <= buf.length`
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* `byteLength` {Number} `0 < byteLength <= 6`
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* `noAssert` {Boolean} Default: false
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* Return: {Number}
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Writes `value` to the buffer at the specified `offset` and `byteLength`.
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Supports up to 48 bits of accuracy. For example:
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var b = new Buffer(6);
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b.writeUIntBE(0x1234567890ab, 0, 6);
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// <Buffer 12 34 56 78 90 ab>
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Set `noAssert` to `true` to skip validation of `value` and `offset`. Defaults
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to `false`.
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### buf.readUIntLE(offset, byteLength[, noAssert])
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### buf.readUIntBE(offset, byteLength[, noAssert])
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### buf.readIntLE(offset, byteLength[, noAssert])
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### buf.readIntBE(offset, byteLength[, noAssert])
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* `offset` {Number} `0 <= offset <= buf.length`
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* `byteLength` {Number} `0 < byteLength <= 6`
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* `noAssert` {Boolean} Default: false
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* Return: {Number}
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A generalized version of all numeric read methods. Supports up to 48 bits of
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accuracy. For example:
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var b = new Buffer(6);
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b.writeUint16LE(0x90ab, 0);
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b.writeUInt32LE(0x12345678, 2);
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b.readUIntLE(0, 6).toString(16); // Specify 6 bytes (48 bits)
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// output: '1234567890ab'
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Set `noAssert` to true to skip validation of `offset`. This means that `offset`
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may be beyond the end of the buffer. Defaults to `false`.
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### buf.toString([encoding][, start][, end])
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151
lib/buffer.js
151
lib/buffer.js
@ -482,6 +482,37 @@ function checkOffset(offset, ext, length) {
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}
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Buffer.prototype.readUIntLE = function(offset, byteLength, noAssert) {
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offset = offset >>> 0;
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byteLength = byteLength >>> 0;
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if (!noAssert)
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checkOffset(offset, byteLength, this.length);
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var val = this[offset];
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var mul = 1;
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var i = 0;
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while (++i < byteLength && (mul *= 0x100))
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val += this[offset + i] * mul;
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return val;
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};
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Buffer.prototype.readUIntBE = function(offset, byteLength, noAssert) {
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offset = offset >>> 0;
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byteLength = byteLength >>> 0;
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if (!noAssert)
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checkOffset(offset, byteLength, this.length);
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var val = this[offset + --byteLength];
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var mul = 1;
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while (byteLength > 0 && (mul *= 0x100))
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val += this[offset + --byteLength] * mul;
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return val;
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};
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Buffer.prototype.readUInt8 = function(offset, noAssert) {
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offset = offset >>> 0;
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if (!noAssert)
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@ -530,6 +561,46 @@ Buffer.prototype.readUInt32BE = function(offset, noAssert) {
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};
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Buffer.prototype.readIntLE = function(offset, byteLength, noAssert) {
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offset = offset >>> 0;
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byteLength = byteLength >>> 0;
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if (!noAssert)
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checkOffset(offset, byteLength, this.length);
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var val = this[offset];
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var mul = 1;
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var i = 0;
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while (++i < byteLength && (mul *= 0x100))
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val += this[offset + i] * mul;
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mul *= 0x80;
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if (val >= mul)
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val -= Math.pow(2, 8 * byteLength);
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return val;
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};
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Buffer.prototype.readIntBE = function(offset, byteLength, noAssert) {
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offset = offset >>> 0;
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byteLength = byteLength >>> 0;
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if (!noAssert)
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checkOffset(offset, byteLength, this.length);
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var i = byteLength;
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var mul = 1;
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var val = this[offset + --i];
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while (i > 0 && (mul *= 0x100))
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val += this[offset + --i] * mul;
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mul *= 0x80;
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if (val >= mul)
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val -= Math.pow(2, 8 * byteLength);
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return val;
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};
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Buffer.prototype.readInt8 = function(offset, noAssert) {
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offset = offset >>> 0;
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if (!noAssert)
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@ -623,6 +694,40 @@ function checkInt(buffer, value, offset, ext, max, min) {
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}
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Buffer.prototype.writeUIntLE = function(value, offset, byteLength, noAssert) {
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value = +value;
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offset = offset >>> 0;
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byteLength = byteLength >>> 0;
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if (!noAssert)
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checkInt(this, value, offset, byteLength, Math.pow(2, 8 * byteLength), 0);
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var mul = 1;
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var i = 0;
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this[offset] = value;
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while (++i < byteLength && (mul *= 0x100))
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this[offset + i] = (value / mul) >>> 0;
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return offset + byteLength;
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};
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Buffer.prototype.writeUIntBE = function(value, offset, byteLength, noAssert) {
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value = +value;
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offset = offset >>> 0;
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byteLength = byteLength >>> 0;
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if (!noAssert)
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checkInt(this, value, offset, byteLength, Math.pow(2, 8 * byteLength), 0);
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var i = byteLength - 1;
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var mul = 1;
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this[offset + i] = value;
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while (--i >= 0 && (mul *= 0x100))
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this[offset + i] = (value / mul) >>> 0;
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return offset + byteLength;
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};
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Buffer.prototype.writeUInt8 = function(value, offset, noAssert) {
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value = +value;
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offset = offset >>> 0;
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@ -681,6 +786,52 @@ Buffer.prototype.writeUInt32BE = function(value, offset, noAssert) {
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};
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Buffer.prototype.writeIntLE = function(value, offset, byteLength, noAssert) {
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value = +value;
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offset = offset >>> 0;
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if (!noAssert) {
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checkInt(this,
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value,
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offset,
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byteLength,
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Math.pow(2, 8 * byteLength - 1) - 1,
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-Math.pow(2, 8 * byteLength - 1));
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}
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var i = 0;
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var mul = 1;
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var sub = value < 0 ? 1 : 0;
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this[offset] = value;
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while (++i < byteLength && (mul *= 0x100))
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this[offset + i] = ((value / mul) >> 0) - sub;
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return offset + byteLength;
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};
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Buffer.prototype.writeIntBE = function(value, offset, byteLength, noAssert) {
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value = +value;
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offset = offset >>> 0;
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if (!noAssert) {
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checkInt(this,
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value,
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offset,
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byteLength,
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Math.pow(2, 8 * byteLength - 1) - 1,
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-Math.pow(2, 8 * byteLength - 1));
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}
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var i = byteLength - 1;
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var mul = 1;
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var sub = value < 0 ? 1 : 0;
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this[offset + i] = value;
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while (--i >= 0 && (mul *= 0x100))
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this[offset + i] = ((value / mul) >> 0) - sub;
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return offset + byteLength;
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};
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Buffer.prototype.writeInt8 = function(value, offset, noAssert) {
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value = +value;
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offset = offset >>> 0;
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@ -950,8 +950,6 @@ var buf = new Buffer([0xFF]);
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assert.equal(buf.readUInt8(0), 255);
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assert.equal(buf.readInt8(0), -1);
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[16, 32].forEach(function(bits) {
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var buf = new Buffer(bits / 8 - 1);
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@ -988,6 +986,91 @@ assert.equal(buf.readInt8(0), -1);
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(0xFFFFFFFF >> (32 - bits)));
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});
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// test for common read(U)IntLE/BE
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(function() {
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var buf = new Buffer([0x01, 0x02, 0x03, 0x04, 0x05, 0x06]);
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assert.equal(buf.readUIntLE(0, 1), 0x01);
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assert.equal(buf.readUIntBE(0, 1), 0x01);
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assert.equal(buf.readUIntLE(0, 3), 0x030201);
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assert.equal(buf.readUIntBE(0, 3), 0x010203);
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assert.equal(buf.readUIntLE(0, 5), 0x0504030201);
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assert.equal(buf.readUIntBE(0, 5), 0x0102030405);
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assert.equal(buf.readUIntLE(0, 6), 0x060504030201);
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assert.equal(buf.readUIntBE(0, 6), 0x010203040506);
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assert.equal(buf.readIntLE(0, 1), 0x01);
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assert.equal(buf.readIntBE(0, 1), 0x01);
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assert.equal(buf.readIntLE(0, 3), 0x030201);
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assert.equal(buf.readIntBE(0, 3), 0x010203);
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assert.equal(buf.readIntLE(0, 5), 0x0504030201);
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assert.equal(buf.readIntBE(0, 5), 0x0102030405);
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assert.equal(buf.readIntLE(0, 6), 0x060504030201);
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assert.equal(buf.readIntBE(0, 6), 0x010203040506);
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})();
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// test for common write(U)IntLE/BE
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(function() {
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var buf = new Buffer(3);
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buf.writeUIntLE(0x123456, 0, 3);
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assert.deepEqual(buf.toJSON().data, [0x56, 0x34, 0x12]);
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assert.equal(buf.readUIntLE(0, 3), 0x123456);
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buf = new Buffer(3);
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buf.writeUIntBE(0x123456, 0, 3);
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assert.deepEqual(buf.toJSON().data, [0x12, 0x34, 0x56]);
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assert.equal(buf.readUIntBE(0, 3), 0x123456);
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buf = new Buffer(3);
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buf.writeIntLE(0x123456, 0, 3);
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assert.deepEqual(buf.toJSON().data, [0x56, 0x34, 0x12]);
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assert.equal(buf.readIntLE(0, 3), 0x123456);
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buf = new Buffer(3);
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buf.writeIntBE(0x123456, 0, 3);
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assert.deepEqual(buf.toJSON().data, [0x12, 0x34, 0x56]);
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assert.equal(buf.readIntBE(0, 3), 0x123456);
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buf = new Buffer(3);
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buf.writeIntLE(-0x123456, 0, 3);
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assert.deepEqual(buf.toJSON().data, [0xaa, 0xcb, 0xed]);
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assert.equal(buf.readIntLE(0, 3), -0x123456);
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buf = new Buffer(3);
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buf.writeIntBE(-0x123456, 0, 3);
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assert.deepEqual(buf.toJSON().data, [0xed, 0xcb, 0xaa]);
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assert.equal(buf.readIntBE(0, 3), -0x123456);
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buf = new Buffer(5);
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buf.writeUIntLE(0x1234567890, 0, 5);
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assert.deepEqual(buf.toJSON().data, [0x90, 0x78, 0x56, 0x34, 0x12]);
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assert.equal(buf.readUIntLE(0, 5), 0x1234567890);
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buf = new Buffer(5);
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buf.writeUIntBE(0x1234567890, 0, 5);
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assert.deepEqual(buf.toJSON().data, [0x12, 0x34, 0x56, 0x78, 0x90]);
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assert.equal(buf.readUIntBE(0, 5), 0x1234567890);
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buf = new Buffer(5);
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buf.writeIntLE(0x1234567890, 0, 5);
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assert.deepEqual(buf.toJSON().data, [0x90, 0x78, 0x56, 0x34, 0x12]);
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assert.equal(buf.readIntLE(0, 5), 0x1234567890);
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buf = new Buffer(5);
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buf.writeIntBE(0x1234567890, 0, 5);
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assert.deepEqual(buf.toJSON().data, [0x12, 0x34, 0x56, 0x78, 0x90]);
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assert.equal(buf.readIntBE(0, 5), 0x1234567890);
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buf = new Buffer(5);
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buf.writeIntLE(-0x1234567890, 0, 5);
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assert.deepEqual(buf.toJSON().data, [0x70, 0x87, 0xa9, 0xcb, 0xed]);
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assert.equal(buf.readIntLE(0, 5), -0x1234567890);
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buf = new Buffer(5);
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buf.writeIntBE(-0x1234567890, 0, 5);
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assert.deepEqual(buf.toJSON().data, [0xed, 0xcb, 0xa9, 0x87, 0x70]);
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assert.equal(buf.readIntBE(0, 5), -0x1234567890);
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})();
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// test Buffer slice
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(function() {
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var buf = new Buffer('0123456789');
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