diff --git a/core/src/matrix/mask.rs b/core/src/matrix/mask.rs
index c1fcfd4..e8c6421 100644
--- a/core/src/matrix/mask.rs
+++ b/core/src/matrix/mask.rs
@@ -1 +1,249 @@
-// FIXME: 掩码评分 — Task 8
+use crate::matrix::grid::Matrix;
+
+/// 掩码函数: f(x, y) = true 时翻转该模块
+type MaskFn = fn(u8, u8) -> bool;
+
+/// 8 种标准 QR 掩码
+pub const MASK_FNS: [MaskFn; 8] = [
+    |x, y| (x + y) % 2 == 0,
+    |_, y| y % 2 == 0,
+    |x, _| x % 3 == 0,
+    |x, y| (x + y) % 3 == 0,
+    |x, y| ((y / 2) + (x / 3)) % 2 == 0,
+    |x, y| (x as u32 * y as u32) % 2 + (x as u32 * y as u32) % 3 == 0,
+    |x, y| ((x as u32 * y as u32) % 2 + (x as u32 * y as u32) % 3) % 2 == 0,
+    |x, y| ((x as u32 + y as u32) % 2 + (x as u32 * y as u32) % 3) % 2 == 0,
+];
+
+/// 应用掩码到矩阵的数据区域（跳过功能图案保留区域）
+pub fn apply_mask(matrix: &Matrix, mask_idx: u8) -> Matrix {
+    let mask_fn = MASK_FNS[mask_idx as usize];
+    let mut result = matrix.clone();
+    for y in 0..matrix.size {
+        for x in 0..matrix.size {
+            if !matrix.is_reserved(x, y) && mask_fn(x, y) {
+                let current = result.get(x, y);
+                result.set(x, y, !current);
+            }
+        }
+    }
+    result
+}
+
+/// 惩罚评分（越低越好）
+pub fn score(matrix: &Matrix) -> u32 {
+    score_rule1(matrix) + score_rule2(matrix) + score_rule3(matrix) + score_rule4(matrix)
+}
+
+/// 规则 1: 连续 5+ 同色行/列 → N1 + k - 5
+fn score_rule1(matrix: &Matrix) -> u32 {
+    let mut penalty = 0u32;
+    let n = matrix.size as usize;
+
+    // 水平扫描
+    for y in 0..n {
+        let mut run = 1u32;
+        let mut prev = matrix.get(0, y as u8);
+        for x in 1..n {
+            let cur = matrix.get(x as u8, y as u8);
+            if cur == prev {
+                run += 1;
+            } else {
+                if run >= 5 {
+                    penalty += 3 + run - 5;
+                }
+                run = 1;
+                prev = cur;
+            }
+        }
+        if run >= 5 {
+            penalty += 3 + run - 5;
+        }
+    }
+
+    // 垂直扫描
+    for x in 0..n {
+        let mut run = 1u32;
+        let mut prev = matrix.get(x as u8, 0);
+        for y in 1..n {
+            let cur = matrix.get(x as u8, y as u8);
+            if cur == prev {
+                run += 1;
+            } else {
+                if run >= 5 {
+                    penalty += 3 + run - 5;
+                }
+                run = 1;
+                prev = cur;
+            }
+        }
+        if run >= 5 {
+            penalty += 3 + run - 5;
+        }
+    }
+
+    penalty
+}
+
+/// 规则 2: 同色 2×2 方块，每个 +3
+fn score_rule2(matrix: &Matrix) -> u32 {
+    let mut count = 0u32;
+    let n = matrix.size;
+    for y in 0..n - 1 {
+        for x in 0..n - 1 {
+            let v = matrix.get(x, y);
+            if matrix.get(x + 1, y) == v
+                && matrix.get(x, y + 1) == v
+                && matrix.get(x + 1, y + 1) == v
+            {
+                count += 1;
+            }
+        }
+    }
+    count * 3
+}
+
+/// 规则 3: 检测 1011101 模式（及其反转），每次 +40
+fn score_rule3(matrix: &Matrix) -> u32 {
+    let mut penalty = 0u32;
+    let n = matrix.size as usize;
+
+    // 水平方向
+    for y in 0..n {
+        for x in 0..n {
+            if x + 10 >= n {
+                continue;
+            }
+            // 正模式: 10111010000
+            let forward = (0..11).all(|i| {
+                let expected = [
+                    true, false, true, true, true, false, true, false, false, false, false,
+                ][i];
+                matrix.get((x + i) as u8, y as u8) == expected
+            });
+            if forward {
+                penalty += 40;
+            }
+
+            // 反模式: 00001011101
+            let reverse = (0..11).all(|i| {
+                let expected = [
+                    false, false, false, false, true, false, true, true, true, false, true,
+                ][i];
+                matrix.get((x + i) as u8, y as u8) == expected
+            });
+            if reverse {
+                penalty += 40;
+            }
+        }
+    }
+
+    // 垂直方向
+    for y in 0..n {
+        if y + 10 >= n {
+            continue;
+        }
+        for x in 0..n {
+            let forward = (0..11).all(|i| {
+                let expected = [
+                    true, false, true, true, true, false, true, false, false, false, false,
+                ][i];
+                matrix.get(x as u8, (y + i) as u8) == expected
+            });
+            if forward {
+                penalty += 40;
+            }
+
+            let reverse = (0..11).all(|i| {
+                let expected = [
+                    false, false, false, false, true, false, true, true, true, false, true,
+                ][i];
+                matrix.get(x as u8, (y + i) as u8) == expected
+            });
+            if reverse {
+                penalty += 40;
+            }
+        }
+    }
+
+    penalty
+}
+
+/// 规则 4: 暗模块占比偏离 50%，每 5% +10
+fn score_rule4(matrix: &Matrix) -> u32 {
+    let total = (matrix.size as u32) * (matrix.size as u32);
+    let dark: u32 = (0..matrix.size)
+        .flat_map(|y| (0..matrix.size).map(move |x| matrix.get(x, y) as u32))
+        .sum();
+
+    let pct = (dark * 100 + total / 2) / total; // 四舍五入
+    let deviation = ((pct as i32 - 50).unsigned_abs()) / 5;
+    deviation * 10
+}
+
+/// 评估所有 8 种掩码，返回最佳掩码编号和对应矩阵
+pub fn best_mask(matrix: &Matrix) -> (u8, Matrix) {
+    let mut best_idx = 0u8;
+    let mut best_score = u32::MAX;
+    let mut best_matrix = matrix.clone();
+
+    for i in 0..8u8 {
+        let masked = apply_mask(matrix, i);
+        let s = score(&masked);
+        if s < best_score {
+            best_score = s;
+            best_idx = i;
+            best_matrix = masked;
+        }
+    }
+
+    (best_idx, best_matrix)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_apply_mask() {
+        let m = Matrix::new(21);
+        // 不设置 reserved，所有区域都是数据区
+        let masked = apply_mask(&m, 0); // (x+y) % 2 == 0
+        // 初始全白，掩码 0 会在 (x+y)%2==0 的位置翻转
+        assert_eq!(masked.get(0, 0), true); // (0+0)%2=0 → 翻转
+        assert_eq!(masked.get(1, 0), false); // (1+0)%2=1 → 不变
+    }
+
+    #[test]
+    fn test_score_rule2() {
+        let mut m = Matrix::new(3);
+        // 全黑 → 4 个 2×2 方块
+        for y in 0..3u8 {
+            for x in 0..3u8 {
+                m.set(x, y, true);
+            }
+        }
+        assert_eq!(score_rule2(&m), 4 * 3); // 4 blocks × 3 = 12
+    }
+
+    #[test]
+    fn test_score_rule4() {
+        let m = Matrix::new(10);
+        // 全部白色 → 0% dark → 偏离 50% = 10 × 5% → penalty = 10 × 10 = 100
+        let s = score_rule4(&m);
+        assert_eq!(s, 100);
+    }
+
+    #[test]
+    fn test_best_mask_selects_something() {
+        let mut m = Matrix::new(21);
+        // 填一些随机数据
+        for y in 0..21u8 {
+            for x in 0..21u8 {
+                m.set(x, y, (x as u32 * y as u32) % 3 == 0);
+            }
+        }
+        let (idx, _masked) = best_mask(&m);
+        assert!(idx < 8);
+    }
+}
diff --git a/core/src/matrix/placement.rs b/core/src/matrix/placement.rs
index e63148f..b7b4861 100644
--- a/core/src/matrix/placement.rs
+++ b/core/src/matrix/placement.rs
@@ -1 +1,80 @@
-// FIXME: 数据排列 — Task 8
+use crate::matrix::grid::Matrix;
+
+/// 将码字比特按蛇形路径放入矩阵数据区域
+pub fn place_data(matrix: &mut Matrix, codewords: &[u8]) {
+    let size = matrix.size as usize;
+    // 展开字节为比特流
+    let bits: Vec<bool> = codewords
+        .iter()
+        .flat_map(|&cw| (0..8).rev().map(move |i| (cw >> i) & 1 == 1))
+        .collect();
+
+    let mut bit_idx = 0usize;
+
+    // 从右下角开始，向上扫描
+    let mut col = (size - 1) as i16;
+    let mut going_up = true;
+
+    while col >= 0 && bit_idx < bits.len() {
+        // 跳过垂直时序线 (col=6)
+        let actual_col = if col == 6 { 5 } else { col as usize };
+
+        if going_up {
+            for row in (0..size).rev() {
+                if bit_idx >= bits.len() {
+                    break;
+                }
+                place_bit(
+                    matrix,
+                    actual_col as u8,
+                    row as u8,
+                    bits[bit_idx],
+                    &mut bit_idx,
+                );
+                if bit_idx >= bits.len() {
+                    break;
+                }
+                place_bit(
+                    matrix,
+                    (actual_col - 1) as u8,
+                    row as u8,
+                    bits[bit_idx],
+                    &mut bit_idx,
+                );
+            }
+        } else {
+            for row in 0..size {
+                if bit_idx >= bits.len() {
+                    break;
+                }
+                place_bit(
+                    matrix,
+                    actual_col as u8,
+                    row as u8,
+                    bits[bit_idx],
+                    &mut bit_idx,
+                );
+                if bit_idx >= bits.len() {
+                    break;
+                }
+                place_bit(
+                    matrix,
+                    (actual_col - 1) as u8,
+                    row as u8,
+                    bits[bit_idx],
+                    &mut bit_idx,
+                );
+            }
+        }
+
+        col -= 2;
+        going_up = !going_up;
+    }
+}
+
+fn place_bit(matrix: &mut Matrix, x: u8, y: u8, bit: bool, idx: &mut usize) {
+    if x < matrix.size && y < matrix.size && !matrix.is_reserved(x, y) {
+        matrix.set(x, y, bit);
+        *idx += 1;
+    }
+}