fix: 4 个 CRITICAL bug 修复

- C1: placement.rs 删除列偏移特殊处理 (col==6→5)，place_bit 已自动跳过保留区
- C2: version.rs V5-H 纠错表 h_g1: 4→2 (总码字数 200→134)
- C3: mode.rs Kanji 编码删除冗余 if/else 重复分支
- C4: galois.rs div() 返回 Option<u8> 替代 panic!

core/src/ecc/galois.rs

@@ -65,19 +65,19 @@ pub fn mul(a: u8, b: u8) -> u8 {
     exp_table()[log_a + log_b]
 }
 
-/// GF(2⁸) 除法：a / b
+/// GF(2⁸) 除法：a / b，b == 0 时返回 None
 #[inline]
-pub fn div(a: u8, b: u8) -> u8 {
+pub fn div(a: u8, b: u8) -> Option<u8> {
     if a == 0 {
-        return 0;
+        return Some(0);
     }
     if b == 0 {
-        panic!("GF(2⁸) 除以零");
+        return None;
     }
     let log_a = log_table()[a as usize] as usize;
     let log_b = log_table()[b as usize] as usize;
     let diff = (log_a + 255 - log_b) % 255;
-    exp_table()[diff]
+    Some(exp_table()[diff])
 }
 
 /// GF(2⁸) 幂运算：base^exp
@@ -134,7 +134,7 @@ mod tests {
     #[test]
     fn test_div_inverse() {
         for a in 1..=255u8 {
-            let inv = div(1, a);
+            let inv = div(1, a).unwrap();
             assert_eq!(mul(a, inv), 1, "逆元失败: {:02X} * {:02X} != 1", a, inv);
         }
     }
@@ -143,7 +143,7 @@ mod tests {
     fn test_div_mul_consistency() {
         for a in 1..=255u8 {
             for b in (1..=255u8).step_by(17) {
-                let q = div(a, b);
+                let q = div(a, b).unwrap();
                 assert_eq!(
                     mul(q, b),
                     a,
@@ -167,9 +167,8 @@ mod tests {
     }
 
     #[test]
-    #[should_panic(expected = "除以零")]
-    fn test_div_by_zero_panics() {
-        div(1, 0);
+    fn test_div_by_zero_returns_none() {
+        assert_eq!(div(1, 0), None);
     }
 
     #[test]

core/src/encoder/bitstream.rs

@@ -31,10 +31,10 @@ pub fn build_codewords(text: &str, version: Version, level: EcLevel) -> Vec<u8>
     // 2. 终止符（最多 4 bit 0）
     let total_capacity = get_data_capacity(version, level) as usize * 8;
     let terminator_len = 4usize.min(total_capacity.saturating_sub(bits.len()));
-    bits.extend(std::iter::repeat(false).take(terminator_len));
+    bits.extend(std::iter::repeat_n(false, terminator_len));
 
     // 3. 补零到 8-bit 边界
-    while bits.len() % 8 != 0 {
+    while !bits.len().is_multiple_of(8) {
         bits.push(false);
     }
 

core/src/encoder/mode.rs

@@ -158,22 +158,14 @@ fn unicode_to_shift_jis(c: char) -> Option<u16> {
         // 简化映射: 用 Unicode 码位偏移做近似
         // 真实转换需要完整映射表，这里做合理近似
         let base = code - 0x4E00;
-        let hi = 0x81 + (base / 0xBC) as u32;
-        let lo = 0x40 + (base % 0xBC) as u32;
+        let hi = 0x81 + (base / 0xBC);
+        let lo = 0x40 + (base % 0xBC);
         let sjis = ((hi << 8) | lo) as u16;
-        // 映射到 13-bit 码字
-        let val = if sjis <= 0x9FFC {
-            let h = (sjis >> 8) as u16;
-            let l = (sjis & 0xFF) as u16;
-            if h >= 0x81 && h <= 0x9F {
-                (h - 0x81) * 0xBC + (l - 0x40)
-            } else {
-                (h - 0xC1) * 0xBC + (l - 0x40)
-            }
-        } else {
-            let h = (sjis >> 8) as u16;
-            let l = (sjis & 0xFF) as u16;
-            if h >= 0x81 && h <= 0x9F {
+        // 映射到 13-bit 码字（内层 if/else 已区分两个 Shift-JIS 区间）
+        let val = {
+            let h = (sjis >> 8);
+            let l = (sjis & 0xFF);
+            if (0x81..=0x9F).contains(&h) {
                 (h - 0x81) * 0xBC + (l - 0x40)
             } else {
                 (h - 0xC1) * 0xBC + (l - 0x40)

core/src/matrix/mask.rs

@@ -11,8 +11,8 @@ pub const MASK_FNS: [MaskFn; 8] = [
     |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,
+    |x, y| ((x as u32 * y as u32) % 2 + (x as u32 * y as u32) % 3).is_multiple_of(2),
+    |x, y| ((x as u32 + y as u32) % 2 + (x as u32 * y as u32) % 3).is_multiple_of(2),
 ];
 
 /// 应用掩码到矩阵的数据区域（跳过功能图案保留区域）

core/src/matrix/placement.rs

@@ -16,8 +16,8 @@ pub fn place_data(matrix: &mut Matrix, codewords: &[u8]) {
     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 };
+        // 列 6 是垂直时序图案，place_bit 会自动跳过保留区
+        let actual_col = col as usize;
 
         if going_up {
             for row in (0..size).rev() {

core/src/version.rs

@@ -1,5 +1,5 @@
-use std::sync::OnceLock;
 use serde::Serialize;
+use std::sync::OnceLock;
 
 /// 纠错级别
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize)]
@@ -272,7 +272,7 @@ static VERSION_TABLE: [VersionRow; 40] = [
         q_g2_data: 16,
         h_total: 134,
         h_ec: 22,
-        h_g1: 4,
+        h_g1: 2,
         h_g1_data: 11,
         h_g2: 2,
         h_g2_data: 12,