英文:
On-purpose int overflow
问题
我正在使用哈希函数murmur2，它返回一个uint64类型的值。
然后我想将其存储在只支持BIGINT（有符号64位）的PostgreSQL中。
由于我对数字本身不感兴趣，只对二进制值感兴趣（因为我将其用作检测唯一性的标识符，我的值集合大约有1000个值，64位哈希对我来说足够了），我想通过“仅仅”更改类型将其转换为int64。
如何以一种让编译器满意的方式做到这一点？
英文:
I'm using the hash function murmur2 which returns me an uint64.
I want then to store it in PostgreSQL, which only support BIGINT (signed 64 bits).
As I'm not interested in the number itself, but just the binary value (as I use it as an id for detecting uniqueness (my set of values being of ~1000 values, a 64bit hash is enough for me) I would like to convert it into int64 by "just" changing the type.
How does one do that in a way that pleases the compiler?
答案1
得分: 7
你可以简单地使用类型转换：
i := uint64(0xffffffffffffffff)
i2 := int64(i)
fmt.Println(i, i2)
输出：
18446744073709551615 -1
将 uint64 转换为 int64 总是成功的：它不会改变内存表示，只是改变了类型。可能会让你困惑的是，如果你尝试将无类型整数常量值转换为 int64：
i3 := int64(0xffffffffffffffff) // 编译时错误！
这是一个编译时错误，因为常量值 0xffffffffffffffff（使用任意精度表示）无法适应 int64，因为适应 int64 的最大值是 0x7fffffffffffffff：
constant 18446744073709551615 overflows int64
英文:
You can simply use a type conversion:
i := uint64(0xffffffffffffffff)
i2 := int64(i)
fmt.Println(i, i2)
Output:
18446744073709551615 -1
Converting uint64 to int64 always succeeds: it doesn't change the memory representation just the type. What may confuse you is if you try to convert an untyped integer constant value to int64:
i3 := int64(0xffffffffffffffff) // Compile time error!
This is a compile time error as the constant value 0xffffffffffffffff (which is represented with arbitrary precision) does not fit into int64 because the max value that fits into int64 is 0x7fffffffffffffff:
constant 18446744073709551615 overflows int64
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