如何将`f64`将其转换为`f32`？

发布于 2025-01-29 14:20:25 字数 377 浏览 3 评论 0原文

如何将f64转换为最近的f32？

从> tryfrom 实现中既没有，这可能是因为此类实现仅用于无损转换。我还搜索了f64文档中的f32的引用，反之亦然，没有发现。

    let double: f64 = 0.;

    // doesn't work
    // let single: f32 = double.into();
    // let single: f32 = double.try_into().unwrap();

原文

How can I convert a f64 into the closest f32?

There is neither a From nor a TryFrom implementation, presumably because such implementations are only provided for lossless conversions. I also searched for references to f32 in the f64 docs and vice versa, and found nothing.

    let double: f64 = 0.;

    // doesn't work
    // let single: f32 = double.into();
    // let single: f32 = double.try_into().unwrap();

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虐人心 2025-02-05 14:20:25

在这种情况下，我们可以将用作铸造的关键字。整数转换通常不需要，因为“从较大的整数到较小的整数（例如U32 - u8）将截断”，通常不想要这一点。对于f64 f32，它非常明智：

从F64到F32的铸造将产生最接近的F32
如有必要，圆形是根据圆形模式
在溢出时，产生了无穷大（与输入相同的符号）
>

    let double: f64 = 42.;
    dbg!(double as f32);

[src/main.rs:13] double as f32 = 42.0

“恐慌而是最简单的解决方案可能是检查is_finite：

fn f64_to_f32(x: f64) -> f32 {
    let y = x as f32;
    assert_eq!(
        x.is_finite(),
        y.is_finite(),
        "f32 overflow during conversion"
    );
    y
}

fn main() {
    dbg!(f64_to_f32(42_f64));
    // dbg!(f64_to_f32(f64::MAX / 10.)); // panics
    dbg!(f64_to_f32(f64::NAN));
    dbg!(f64_to_f32(f64::INFINITY));
    dbg!(f64_to_f32(f64::NEG_INFINITY));
}

[src/main.rs:2] f64_to_f32(42_f64) = 42.0
[src/main.rs:4] f64_to_f32(f64::NAN) = NaN
[src/main.rs:5] f64_to_f32(f64::INFINITY) = inf
[src/main.rs:6] f64_to_f32(f64::NEG_INFINITY) = -inf

In this case, we can use the as keyword for casting. It is usually not desired for integer conversions because "casting from a larger integer to a smaller integer (e.g. u32 -> u8) will truncate", and this is usually not wanted. For f64 to f32, however, it's very sensible:

Casting from an f64 to an f32 will produce the closest possible f32
if necessary, rounding is according to roundTiesToEven mode
on overflow, infinity (of the same sign as the input) is produced
Rust Reference

    let double: f64 = 42.;
    dbg!(double as f32);

[src/main.rs:13] double as f32 = 42.0

If an overflow to infinity is not desired and you want to panic instead, the simplest solution might be to check for is_finite:

fn f64_to_f32(x: f64) -> f32 {
    let y = x as f32;
    assert_eq!(
        x.is_finite(),
        y.is_finite(),
        "f32 overflow during conversion"
    );
    y
}

fn main() {
    dbg!(f64_to_f32(42_f64));
    // dbg!(f64_to_f32(f64::MAX / 10.)); // panics
    dbg!(f64_to_f32(f64::NAN));
    dbg!(f64_to_f32(f64::INFINITY));
    dbg!(f64_to_f32(f64::NEG_INFINITY));
}

[src/main.rs:2] f64_to_f32(42_f64) = 42.0
[src/main.rs:4] f64_to_f32(f64::NAN) = NaN
[src/main.rs:5] f64_to_f32(f64::INFINITY) = inf
[src/main.rs:6] f64_to_f32(f64::NEG_INFINITY) = -inf

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