Implement more From trait mappings, add more docs

src/bigint.rs

@@ -1,57 +1,23 @@
+#![allow(unused_variables)]
 //! \[WIP\] Arbitrarily large integers
-//!
-//! Traits to implement:
-//! * Neg
-//! * Rem
-//! * RemAssign
-//! * Sub
-//! * SubAssign
 use crate::num::*;
 use core::ops::{
     Add, AddAssign, Div, DivAssign, Mul, MulAssign, Neg, Not, Rem, RemAssign, Sub, SubAssign,
 };
+use core::usize;
+use std::convert::TryInto;
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, PartialEq)]
 pub struct BigInt {
     inner: Vec<usize>,
     sign: Sign,
 }
 
-macro_rules! impl_from_smaller {
-    ($($Type: ty),* ) => {
-        $(
-            impl From<$Type> for BigInt {
-                fn from(n: $Type) -> Self {
-                    let mut new = Self::default();
-                    new.inner[0] = n as usize;
-
-                    new
-                }
-            }
-        )*
-    }
-}
-
-#[cfg(target_pointer_width = "16")]
-impl_from_smaller!(u8, u16);
-#[cfg(target_pointer_width = "16")]
-static BITS:usize = 16;
-
-#[cfg(target_pointer_width = "32")]
-impl_from_smaller!(u8, u16, u32);
-#[cfg(target_pointer_width = "32")]
-static BITS:usize = 32;
-
-#[cfg(target_pointer_width = "64")]
-impl_from_smaller!(u8, u16, u32, u64);
-#[cfg(target_pointer_width = "64")]
-static BITS:usize = 64;
-
 impl Default for BigInt {
     fn default() -> Self {
         Self {
             inner: vec![0],
-            sign: Sign::Positive,
+            sign: Sign::default(),
         }
     }
 }
@@ -60,7 +26,7 @@ impl From<usize> for BigInt {
     fn from(n: usize) -> Self {
         Self {
             inner: vec![n],
-            sign: Sign::Positive,
+            sign: Sign::default(),
         }
     }
 }
@@ -78,14 +44,52 @@ impl From<String> for BigInt {
 }
 
 impl BigInt {
+    /// Create a new Bigint, of value 0
+    ///
+    /// The various `From` implementations are more useful in most cases
     pub fn new() -> Self {
         Self::default()
     }
 
-    pub fn shrink_to_fit(&mut self) {
-        todo!();
+    fn new_empty() -> Self {
+        Self {
+            inner: Vec::new(),
+            sign: Sign::Positive,
+        }
     }
 
+    /// Remove digits that are zero from the internal representation.
+    ///
+    /// Similar to 007 -> 7 in base 10
+    pub fn trim_zeros(&mut self) {
+        let current_len = self.inner.len();
+        if current_len < 2 {
+            return
+        }
+
+        let mut trailing_zeros = 0usize;
+        for val in self.inner.iter().rev() {
+            if *val != 0 {
+                break
+            }
+
+            trailing_zeros += 1;
+        }
+
+        let new_len = current_len - trailing_zeros;
+
+        self.inner.truncate(new_len);
+    }
+
+    /// Remove unused digits, and shrink the internal vector
+    pub fn shrink_to_fit(&mut self) {
+        self.trim_zeros();
+        self.inner.shrink_to_fit();
+    }
+
+    /// Convert a `&str` or a `String` representing a number in the specified radix to a Bigint.
+    ///
+    /// For radix 10, use the `from` associated function instead.
     pub fn from_str_radix<T: ToString>(s: T, radix: usize) -> BigInt {
         todo!();
     }
@@ -96,7 +100,7 @@ impl Add for BigInt {
 
     fn add(self, rhs: Self) -> Self::Output {
         // @TODO: handle signs
-        let mut out = BigInt::default();
+        let mut out = BigInt::new_empty();
 
         let u_digits = self.inner.len();
         let v_digits = rhs.inner.len();
@@ -114,22 +118,14 @@ impl Add for BigInt {
 
             let (res, overflowed) = a.overflowing_add(b);
             if overflowed {
-                if i == 0 {
-                    out.inner[i] = res + carry;
-                } else {
-                    out.inner.push(res + carry);
-                }
+                out.inner.push(res + carry);
                 carry = 1;
-            } else {
-                if res < core::usize::MAX {
-                    out.inner.push(res + carry);
-                    carry = 0;
-                } else {
-                    out.inner.push(0usize);
-                    carry = 1;
-                }
-
+            } else if res < core::usize::MAX {
+                out.inner.push(res + carry);
                 carry = 0;
+            } else {
+                out.inner.push(0usize);
+                carry = 1;
             }
         }
 
@@ -141,7 +137,7 @@ impl Sub for BigInt {
     type Output = Self;
 
     fn sub(self, rhs: Self) -> Self::Output {
-        unimplemented!()
+        todo!()
     }
 }
 
@@ -149,7 +145,7 @@ impl Mul for BigInt {
     type Output = Self;
 
     fn mul(self, rhs: Self) -> Self::Output {
-        unimplemented!()
+        todo!()
     }
 }
 
@@ -157,7 +153,7 @@ impl Div for BigInt {
     type Output = Self;
 
     fn div(self, rhs: Self) -> Self::Output {
-        unimplemented!()
+        todo!()
     }
 }
 
@@ -165,7 +161,7 @@ impl Rem for BigInt {
     type Output = Self;
 
     fn rem(self, rhs: Self) -> Self::Output {
-        unimplemented!()
+        todo!()
     }
 }
 
@@ -202,6 +198,7 @@ impl RemAssign for BigInt {
 impl Neg for BigInt {
     type Output = Self;
 
+    /// Flip the sign of the current `BigInt` value
     fn neg(self) -> Self::Output {
         let mut output = self.clone();
         output.sign = !output.sign;
@@ -213,6 +210,7 @@ impl Neg for BigInt {
 impl Not for BigInt {
     type Output = Self;
 
+    /// Do a bitwise negation of every digit's value
     fn not(self) -> Self::Output {
         let mut flipped: Vec<usize> = Vec::with_capacity(self.inner.len());
 
@@ -228,6 +226,79 @@ impl Not for BigInt {
     }
 }
 
+macro_rules! impl_from_smaller {
+    ($(($s: ty, $u: ty)),* ) => {
+        $(
+            impl From<$s> for BigInt {
+                /// Create a `BigInt` from a signed integer primitive
+                fn from(n: $s) -> Self {
+                    let sign = if n < 0 { Sign::Negative } else { Sign::Positive };
+                    let n = n.abs();
+                    let raw: usize = <$s>::try_into(n).unwrap();
+
+                    Self {
+                        inner: vec![raw],
+                        sign,
+                    }
+                }
+            }
+
+            impl From<$u> for BigInt {
+                /// Create a `BigInt` from an unsigned integer primitive
+                fn from(n: $u) -> Self {
+                    let mut new = Self::new_empty();
+                    new.inner.push(n as usize);
+
+                    new
+                }
+            }
+        )*
+    }
+}
+
+macro_rules! impl_from_larger {
+    ($(($s: ty, $u: ty)),* ) => {
+        $(
+            impl From<$s> for BigInt {
+                /// Create a `BigInt` from a signed integer primitive
+                fn from(n: $s) -> Self {
+                    todo!();
+                }
+            }
+
+            impl From<$u> for BigInt {
+                /// Create a `BigInt` from an unsigned integer primitive
+                fn from(n: $u) -> Self {
+                    use core::usize::MAX;
+
+                    let base_usize_value = n / MAX as $u;
+                    let rem = n % MAX as $u;
+
+                    if base_usize_value == 0 {
+                        Self::from(rem as usize)
+                    } else {
+                        todo!();
+                    }
+                }
+            }
+        )*
+    };
+}
+
+#[cfg(target_pointer_width = "32")]
+impl_from_larger!((i64, u64), (i128, u128));
+#[cfg(target_pointer_width = "32")]
+impl_from_smaller!((i8, u8), (i16, u16), (i32, u32));
+#[cfg(target_pointer_width = "32")]
+static BITS:usize = 32;
+
+#[cfg(target_pointer_width = "64")]
+impl_from_larger!((i128, u128));
+#[cfg(target_pointer_width = "64")]
+impl_from_smaller!((i8, u8), (i16, u16), (i32, u32), (i64, u64));
+#[cfg(target_pointer_width = "64")]
+static BITS:usize = 64;
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -285,4 +356,13 @@ mod tests {
         );
         assert_eq!(a.inner[1], 1usize, "most significant place should be 1");
     }
+
+    #[test]
+    fn test_from() {
+        // Signed numbers
+        assert_eq!(-BigInt::from(2), BigInt::from(-2));
+
+        // Larger than usize
+        assert_eq!(BigInt::from(45u128), BigInt::from(45usize));
+    }
 }