1 files changed, 104 insertions, 0 deletions
diff --git a/src/data/float.rs b/src/data/float.rs
new file mode 100644
index 0000000..6115876
--- /dev/null
+++ b/src/data/float.rs
@@ -0,0 +1,104 @@
+// The code that is related to float number handling
+
+fn find_minimal_repr(n: f64, eps: f64) -> (f64, usize) {
+    if eps >= 1.0 {
+        return (n, 0);
+    }
+    if n - n.floor() < eps {
+        (n.floor(), 0)
+    } else if n.ceil() - n < eps {
+        (n.ceil(), 0)
+    } else {
+        let (rem, pre) = find_minimal_repr((n - n.floor()) * 10.0, eps * 10.0);
+        (n.floor() + rem / 10.0, pre + 1)
+    }
+}
+
+fn float_to_string(n: f64, max_precision: usize) -> String {
+    let (sign, n) = if n < 0.0 { ("-", -n) } else { ("", n) };
+    let int_part = n.floor();
+
+    let dec_part =
+        ((n.abs() - int_part.abs()) * (10.0f64).powf(max_precision as f64)).round() as u64;
+
+    if dec_part == 0 || max_precision == 0 {
+        return format!("{}{:.0}", sign, int_part);
+    }
+
+    let mut leading = "".to_string();
+    let mut dec_result = format!("{}", dec_part);
+
+    for _ in 0..(max_precision - dec_result.len()) {
+        leading.push('0');
+    }
+
+    while let Some(c) = dec_result.pop() {
+        if c != '0' {
+            dec_result.push(c);
+            break;
+        }
+    }
+
+    format!("{}{:.0}.{}{}", sign, int_part, leading, dec_result)
+}
+
+/// The function that pretty prints the floating number
+/// Since rust doesn't have anything that can format a float with out appearance, so we just
+/// implemnet a float pretty printing function, which finds the shortest representation of a
+/// floating point number within the allowed error range.
+///
+/// - `n`: The float number to pretty-print
+/// - `allow_sn`: Should we use scientific notation when possible
+/// - **returns**: The pretty printed string
+pub fn pretty_print_float(n: f64, allow_sn: bool) -> String {
+    let (n, p) = find_minimal_repr(n, 1e-10);
+    let d_repr = float_to_string(n, p);
+    if !allow_sn {
+        d_repr
+    } else {
+        if n == 0.0 {
+            return "0".to_string();
+        }
+
+        let mut idx = n.abs().log10().floor();
+        let mut exp = (10.0f64).powf(idx);
+
+        if n.abs() / exp + 1e-5 >= 10.0 {
+            idx += 1.0;
+            exp *= 10.0;
+        }
+
+        if idx.abs() < 3.0 {
+            return d_repr;
+        }
+
+        let (sn, sp) = find_minimal_repr(n / exp, 1e-5);
+        let s_repr = format!("{}e{}", float_to_string(sn, sp), float_to_string(idx, 0));
+        if s_repr.len() + 1 < d_repr.len() {
+            s_repr
+        } else {
+            d_repr
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    #[test]
+    fn test_pretty_printing() {
+        assert_eq!(pretty_print_float(0.99999999999999999999, false), "1");
+        assert_eq!(pretty_print_float(0.9999, false), "0.9999");
+        assert_eq!(
+            pretty_print_float(-1e-5 - 0.00000000000000001, true),
+            "-1e-5"
+        );
+        assert_eq!(
+            pretty_print_float(-1e-5 - 0.00000000000000001, false),
+            "-0.00001"
+        );
+        assert_eq!(pretty_print_float(1e100, true), "1e100");
+        assert_eq!(pretty_print_float(1234567890f64, true), "1234567890");
+        assert_eq!(pretty_print_float(1000000001f64, true), "1e9");
+    }
+}