Added comment with reasoning for number or array BN instantiation.
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@ -94,6 +94,12 @@ BufferReader.prototype.readUInt64LEBN = function() {
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var second = this.buf.readUInt32LE(this.pos);
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var first = this.buf.readUInt32LE(this.pos + 4);
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var combined = (first * 0x100000000) + second;
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// Instantiating an instance of BN with a number is faster than with an
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// array or string. However, the maximum safe number for a double precision
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// floating point is 2 ^ 52 - 1 (0x1fffffffffffff), thus we can safely use
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// non-floating point numbers less than this amount (52 bits). And in the case
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// that the number is larger, we can instatiate an instance of BN by passing
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// an array from the buffer (slower) and specifying the endianness.
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var bn;
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if (combined <= 0x1fffffffffffff) {
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bn = new BN(combined);
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