英文:
When I cast math.NaN() and math.MaxFloat64 to int, Why the result is different between go1.14.2 and go1.17.2?
问题
package main
import (
"fmt"
"math"
)
func main() {
x, y := math.NaN(), math.MaxFloat64
fmt.Printf("%d\n", int(x))
fmt.Printf("%d\n", int(y))
}
这是我的测试代码片段。当我使用go1.14.2运行上述代码时，结果是
-9223372036854775808
-9223372036854775808
但是当我在go1.17.2中运行相同的代码时，结果是
0
9223372036854775807
我搜索了类似的问题：https://stackoverflow.com/questions/70425809/why-is-uint64-of-nan-and-maxfloat64-equal-in-golang，其中提到在不同的硬件环境中，math.NaN()可能是不同的，但是我在我的MacOS M1系统上运行了相同的代码，只是golang版本不同。为什么go1.14.2和go1.17.2之间的结果不同？
英文:
package main
import (
"fmt"
"math"
)
func main() {
x, y := math.NaN(), math.MaxFloat64
fmt.Printf("%d\n", int(x))
fmt.Printf("%d\n", int(y))
}
That is my test code snippet. When I run the above code use go1.14.2, the result is
-9223372036854775808
-9223372036854775808
but the same code run in go1.17.2, the result is
0
9223372036854775807
I searched the simular question: https://stackoverflow.com/questions/70425809/why-is-uint64-of-nan-and-maxfloat64-equal-in-golang, which said that in the different hardware environment, the math.NaN() maybe different, but I run the code both in my MacOS M1 system, just golang version is different. Why the result is different between go1.14.2 and go1.17.2?
答案1
得分: 1
> 在涉及浮点数或复数值的所有非常量转换中，如果结果类型无法表示该值，则转换成功，但结果值取决于实现。
你将浮点数值 NaN 转换为 int。int 类型的有效值不包括 NaN 值，因此你转换的值无法用 int 类型的值表示，所以结果取决于实现。基本上，规范允许在不同版本、不同平台上进行更改。你不能（也不应该）假设转换结果的特定 int 值。
英文:
> In all non-constant conversions involving floating-point or complex values, if the result type cannot represent the value the conversion succeeds but the result value is implementation-dependent.
You convert the floating-point value NaN to int. The valid values of the int type does not include the NaN value, so the value you convert cannot be represented by a value of type int, so the result is implementation-dependent. Basically, the spec allows it to be changed from version to version, from platform to platform. You cannot (should not) assume a specific int value for the conversion result.
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