Is There a Faster Way to Check if a big.Int is Zero?

Is there a faster way of testing if a big.Int is 0?

Problem:

When working with big.Ints, it's often necessary to test if the value is 0. While comparing the big.Int to a big.Int representing 0 (e.g., zero := big.NewInt(0)) works, is there a quicker way specifically for 0?

Solution:

Yes, there are two ways to test for 0 that are significantly faster than comparing to another big.Int:

1. Check the Bits Slice Length:

big.Int exposes the Bits() method, which returns a slice of bytes representing the internal binary representation of the value. For 0, this slice will be empty (nil). Therefore, you can simply check if the length of the bits slice is 0:

if len(i1.Bits()) == 0 {
}

2. Check the Bit Length:

The BitLen() method returns the number of bits required to represent the value. For 0, the bit length is 0. Hence, you can also use this:

if i1.BitLen() == 0 {
}

Benchmark Results:

Compared to the traditional comparison approach, both of the above methods provide significant performance improvements:

BenchmarkCompare-8      76975251            13.3 ns/op
BenchmarkBits-8         1000000000           0.656 ns/op
BenchmarkBitLen-8       1000000000           1.11 ns/op

Testing for 1

While not as fast as testing for 0, a similar approach can be used to test if a big.Int is equal to 1: check if the bits content represents 1 and the sign is positive.

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