第八版

chanlun/src/utils/format.rs

@@ -22,6 +22,7 @@
  * SOFTWARE.
  */
 
+/// 将 f64 格式化为与 Python `:g` (6 位有效数字) 兼容的字符串。
 pub fn format_f64_g(value: f64) -> String {
     if value.is_nan() {
         return "nan".to_string();
@@ -33,9 +34,61 @@ pub fn format_f64_g(value: f64) -> String {
             "-inf".to_string()
         };
     }
+    if value == 0.0 {
+        return "0".to_string();
+    }
 
-    // Use high precision then trim trailing zeros
-    let s = format!("{:.15}", value);
-    let s = s.trim_end_matches('0');
-    s.trim_end_matches('.').to_string()
+    let abs = value.abs();
+    let exp = abs.log10().floor() as i32;
+
+    // Python :g 科学计数法边界: exp < -4 或 exp >= p (=6)
+    if exp < -4 || exp >= 6 {
+        let significand = value / 10_f64.powi(exp);
+        let s = format!("{:.5}", significand);
+        let s = s.trim_end_matches('0').trim_end_matches('.');
+        return format!("{}e{:+03}", s, exp);
+    }
+
+    // 定点表示
+    if abs >= 1.0 {
+        let int_digits = exp as usize + 1;
+        if int_digits >= 6 {
+            return format!("{:.0}", value);
+        }
+        let s = format!("{:.prec$}", value, prec = 6 - int_digits);
+        let s = s.trim_end_matches('0');
+        return s.trim_end_matches('.').to_string();
+    } else {
+        let leading_zeros = (-exp) as usize;
+        let s = format!("{:.prec$}", value, prec = leading_zeros + 5);
+        let s = s.trim_end_matches('0');
+        return s.trim_end_matches('.').to_string();
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_format_large() {
+        assert_eq!(format_f64_g(82833.0), "82833");
+        assert_eq!(format_f64_g(74192.2), "74192.2");
+        assert_eq!(format_f64_g(100.0), "100");
+        assert_eq!(format_f64_g(0.0), "0");
+        assert_eq!(format_f64_g(12345.6789), "12345.7");
+    }
+
+    #[test]
+    fn test_format_small() {
+        assert_eq!(format_f64_g(0.001234), "0.001234");
+        assert_eq!(format_f64_g(0.1), "0.1");
+        assert_eq!(format_f64_g(0.001), "0.001");
+    }
+
+    #[test]
+    fn test_format_extreme() {
+        assert_eq!(format_f64_g(1e7), "1e+07");
+        assert_eq!(format_f64_g(1e-5), "1e-05");
+    }
 }