How Can I Most Efficiently Check if a big.Int is Zero?

Faster 0 Test for big.Int

Challenge:

Optimizing code that checks if a big.Int value is equal to 0.

Solution:

Emphasizing efficiency, a direct check of the big.Int's binary representation is recommended over comparison with a zero-initialized instance.

big.Int provides access to its raw byte representation through Int.Bits(). This exposed slice maintains a reference to the underlying array, avoiding costly copies.

Testing for 0:

The documentation specifies that the big.Int zero value equals 0. Hence, an empty Bits() slice indicates a zero value, as nil is the zero value for slices. This check is faster than the conventional comparison:

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

Alternatively, Int.BitLen() can be used, as it confirms that the bit length of 0 is 0:

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

Benchmarks:

Comparative timing demonstrates the significant performance gains:

BenchmarkCompare: 13.3 ns/op
BenchmarkBits: 0.656 ns/op
BenchmarkBitLen: 1.11 ns/op

Additional Note:

Similar optimizations can be applied for testing if a big.Int value equals 1. Although more complex, it involves checking both the bits content and the sign.

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