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【学Rust写CAD】15 定点数实现（fixed.rs）

article 2025/3/31 13:32:44

源代码

fixed.rs文件实现了一个定点数(Fixed Point)类型 Fixed，用于在整数运算中模拟小数运算。代码如下：

//小数位数
const FIXED_FRACTION_BITS: u32 = 16;
//用于 双线性插值（Bilinear Interpolation） 的计算，它决定了插值权重（weight）的精度位数。一般为4或8
const BILINEAR_INTERPOLATION_BITS: u32 = 4;

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub struct Fixed(i32);

impl Fixed {
    pub const ONE: Fixed = Fixed(1 << FIXED_FRACTION_BITS);
    pub const HALF: Fixed = Fixed(1 << (FIXED_FRACTION_BITS-1));//FIXED_ONE
    
    /// 创建新的Fixed值
    pub fn new(value: i32) -> Self {
        Fixed(value)
    }
    
    /// 将浮点数转换为定点数
    pub fn from_float(x: f32) -> Self {
        Fixed(((x * (1 << FIXED_FRACTION_BITS) as f32) + 0.5) as i32)
    }
    
    /// 将定点数转换为整数(截断小数部分)
    pub fn to_int(self) -> i32 {
        self.0 >> FIXED_FRACTION_BITS
    }
    
    /// 获取双线性插值权重
    pub fn bilinear_weight(self) -> u32 {
        // 丢弃不需要的精度位
        let reduced = self.0 >> (FIXED_FRACTION_BITS - BILINEAR_INTERPOLATION_BITS);
        // 提取剩余的小数部分
        let fraction = reduced & ((1 << BILINEAR_INTERPOLATION_BITS) - 1);
        fraction as u32
    }
    
    /// 获取内部值
    pub fn raw_value(self) -> i32 {
        self.0
    }
}

// 实现一些运算符重载以便更方便地使用
impl std::ops::Add for Fixed {
    type Output = Self;
    fn add(self, rhs: Self) -> Self {
        Fixed(self.0 + rhs.0)
    }
}

impl std::ops::Sub for Fixed {
    type Output = Self;
    fn sub(self, rhs: Self) -> Self {
        Fixed(self.0 - rhs.0)
    }
}

impl std::ops::Mul for Fixed {
    type Output = Self;
    fn mul(self, rhs: Self) -> Self {
        // 定点数乘法需要调整小数位
        Fixed((self.0 as i64 * rhs.0 as i64 >> FIXED_FRACTION_BITS) as i32)
    }
}

impl std::ops::Div for Fixed {
    type Output = Self;
    fn div(self, rhs: Self) -> Self {
        // 定点数除法需要调整小数位
        Fixed(((self.0 as i64 << FIXED_FRACTION_BITS) / rhs.0 as i64) as i32)
    }
}

impl std::ops::Shr<u32> for Fixed {
    type Output = Self;
    fn shr(self, rhs: u32) -> Self {
        Fixed(self.0 >> rhs)
    }
}

impl std::ops::Shl<u32> for Fixed {
    type Output = Self;
    fn shl(self, rhs: u32) -> Self {
        Fixed(self.0 << rhs)
    }
}