display

src/lib.rs

@@ -1,10 +1,26 @@
-// #![no_std]
+#![no_std]
 
 use core::{error::Error, fmt::Display};
 #[cfg(not(test))]
 use num_traits::float::FloatCore;
 use num_traits::{one, zero, PrimInt, Unsigned};
 
+#[derive(Debug)]
+pub enum DecimalError {
+    ExponentOverflow,
+    NotANumber,
+}
+
+impl Error for DecimalError {}
+impl Display for DecimalError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            DecimalError::ExponentOverflow => f.write_str("Exponent overflow"),
+            DecimalError::NotANumber => f.write_str("Not a number"),
+        }
+    }
+}
+
 #[derive(Debug, Clone, Copy)]
 pub struct Decimal<const S: usize = 5, E = u16> {
     pub minus: bool,
@@ -24,19 +40,22 @@ impl<const S: usize, E: PrimInt> Default for Decimal<S, E> {
     }
 }
 
-#[derive(Debug)]
-pub enum DecimalError {
-    ExponentOverflow,
-    NotANumber,
-}
-
-impl Error for DecimalError {}
-impl Display for DecimalError {
+impl<const S: usize, E: Display> Display for Decimal<S, E> {
     fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
-        match self {
-            DecimalError::ExponentOverflow => f.write_str("Exponent overflow"),
-            DecimalError::NotANumber => f.write_str("Not a number"),
+        if self.minus {
+            write!(f, "-")?;
         }
+        for i in 0..S {
+            write!(f, "{}", self.significant[i])?;
+            if i == 0 {
+                write!(f, ".")?;
+            }
+        }
+        write!(f, "e")?;
+        if self.minus_exponent {
+            write!(f, "-")?;
+        }
+        write!(f, "{}", self.exponent)
     }
 }
 
@@ -120,6 +139,7 @@ impl<const S: usize, E: PrimInt + Unsigned> TryFrom<Decimal<S, E>> for f64 {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use arrayvec::ArrayString;
 
     #[test]
     fn float_to_decimal_zero() {
@@ -259,4 +279,40 @@ mod tests {
         let dec = Decimal::<16>::try_from(f64::MAX).unwrap();
         assert_eq!(f64::try_from(dec).unwrap(), f64::MAX);
     }
+
+    #[test]
+    fn decimal_display_zero() {
+        use core::fmt::Write;
+        let dec = Decimal::<7>::try_from(0.0).unwrap();
+        let mut str: ArrayString<100> = ArrayString::new();
+        write!(str, "{}", dec).unwrap();
+        assert_eq!("0.000000e0", str.as_str());
+    }
+
+    #[test]
+    fn decimal_display_pos_big() {
+        use core::fmt::Write;
+        let dec = Decimal::<7>::try_from(1337.42).unwrap();
+        let mut str: ArrayString<100> = ArrayString::new();
+        write!(str, "{}", dec).unwrap();
+        assert_eq!("1.337420e3", str.as_str());
+    }
+
+    #[test]
+    fn decimal_display_neg_big() {
+        use core::fmt::Write;
+        let dec = Decimal::<7>::try_from(-1337.42).unwrap();
+        let mut str: ArrayString<100> = ArrayString::new();
+        write!(str, "{}", dec).unwrap();
+        assert_eq!("-1.337420e3", str.as_str());
+    }
+
+    #[test]
+    fn decimal_display_neg_small() {
+        use core::fmt::Write;
+        let dec = Decimal::<7>::try_from(-0.0133742).unwrap();
+        let mut str: ArrayString<100> = ArrayString::new();
+        write!(str, "{}", dec).unwrap();
+        assert_eq!("-1.337420e-2", str.as_str());
+    }
 }