Is There a Faster Way to Check if a big.Int is Zero Than Cmp(zero)?

Alternatives to Cmp(zero) for Testing if a big.Int is 0

When working with big.Ints, testing for the value 0 is a common task. While using Cmp(zero) to compare a big.Int to a zero value is a viable option, this method may not always be the quickest. This article explores alternative methods that can offer improved performance for this specific scenario.

Accessing Raw Byte Representation

big.Int exposes the Int.Bits() method to access the raw bytes of its representation. This slice provides direct access to the integer's internal representation, which is shared with the original big.Int. This means that accessing the bits directly is a performant operation.

Testing for 0

As mentioned in the documentation, the zero value for a big.Int represents the value 0. Therefore, its corresponding slice will be empty. By checking the length of this slice, we can efficiently determine if the big.Int is 0:

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

Alternatively, the Int.BitLen() function returns the bit length of a big.Int. Since the bit length of 0 is also 0, this method can be used similarly:

if i1.BitLen() == 0 {
    // i1 is 0
}

Benchmark Results

Benchmarking the performance of our proposed methods demonstrates significant improvements over the traditional Cmp(zero) approach:

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

As evident, getting the bits and comparing the slice length to 0 is approximately 20 times faster than Cmp(zero), while using Int.BitLen() is about 10 times faster.

Conclusion

By leveraging the Int.Bits() method and its shared implementation with Int.BitLen(), we can efficiently test if a big.Int is 0 without sacrificing performance. These alternatives offer significant speed advantages for applications that require frequent 0-checking of big integers.

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