How Can I Safely Convert a uint64 to an int64 in Go, Preserving its Binary Representation?

Int Overflow Conversion to int64

In certain scenarios, particularly when dealing with hash functions, developers may need to convert a uint64 value into an int64 while preserving its binary representation. This seems like a straightforward operation, but can be confusing due to the potential for overflow.

For example, the murmur2 hash function generates a uint64 result. When working with PostgreSQL, which only supports int64 (signed 64 bits), developers may desire a type conversion that preserves the hash's binary value.

Fortunately, this conversion is trivial. Simply use a type conversion:

i := uint64(0xffffffffffffffff)
i2 := int64(i)

The resulting output is:

18446744073709551615 -1

It is important to note that the memory representation remains the same after the conversion; only the type is altered.

However, there is a caveat when converting untyped integer constants to int64. For instance:

i3 := int64(0xffffffffffffffff) // Compile time error!

Attempting this conversion results in a compile-time error because the value 0xffffffffffffffff exceeds the maximum int64 value (0x7fffffffffffffff). In such cases, developers must use a uint64 type or handle the conversion explicitly.

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