From d5d973060794e64a3c72826b10c99cff0e51253e Mon Sep 17 00:00:00 2001
From: Timothy Warren <twarren@nabancard.com>
Date: Tue, 3 Mar 2020 16:33:21 -0500
Subject: [PATCH] First shot at adding bigints

---
 src/bigint.rs | 103 +++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 93 insertions(+), 10 deletions(-)

diff --git a/src/bigint.rs b/src/bigint.rs
index a87a461..51e4df6 100644
--- a/src/bigint.rs
+++ b/src/bigint.rs
@@ -20,24 +20,96 @@ pub struct BigInt {
     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 = "32")]
+impl_from_smaller!(u8, u16, u32);
+
+#[cfg(target_pointer_width = "64")]
+impl_from_smaller!(u8, u16, u32, u64);
+
+#[cfg(target_pointer_width = "16")]
+static BITS:usize = 16;
+
+#[cfg(target_pointer_width = "32")]
+static BITS:usize = 32;
+
+#[cfg(target_pointer_width = "64")]
+static BITS:usize = 64;
+
+fn add(u: BigInt, v: BigInt) -> BigInt {
+    let mut out = BigInt::default();
+
+    let u_digits = u.inner.len();
+    let v_digits = v.inner.len();
+
+    let digits = if v_digits > u_digits {
+        v_digits
+    } else {
+        u_digits
+    };
+
+    let mut carry = 0usize;
+    for i in 0..=digits {
+        let a = *u.inner.get(i).unwrap_or(&0usize);
+        let b = *v.inner.get(i).unwrap_or(&0usize);
+
+        let (res, overflowed) = a.overflowing_add(b);
+        // assert!(!overflowed, "Expected to overflow: {:#?}", (res, overflowed));
+        if overflowed {
+            if i == 0 {
+               out.inner[i] = res;
+            } else {
+                out.inner.push(res);
+            }
+            carry = core::usize::MAX - res + 1;
+        } else {
+            if res < core::usize::MAX {
+                out.inner.push(res + carry);
+                carry = 0;
+            } else {
+                out.inner.push(0usize);
+                carry = 1;
+            }
+
+            carry = 0;
+        }
+    }
+
+    out
+}
+
 impl Default for BigInt {
     fn default() -> Self {
         Self {
-            inner: vec![],
+            inner: vec![0],
             sign: Sign::Positive,
         }
     }
 }
 
-impl<T: Unsigned> From<T> for BigInt {
-    fn from(n: T) -> Self {
-        let mut new = Self::default();
-
-        if n > T::max_value() {
-            new.split(n);
+impl From<usize> for BigInt {
+    fn from(n: usize) -> Self {
+        Self {
+            inner: vec![n],
+            sign: Sign::Positive,
         }
-
-        new
     }
 }
 
@@ -84,6 +156,17 @@ mod tests {
 
     #[test]
     fn sanity_checks() {
-
+        let int = BigInt::from(45u8);
+        assert_eq!(int.inner[0], 45usize)
     }
+
+    /* #[test]
+    fn test_add() {
+        let a = BigInt::from(core::u64::MAX);
+        let b = BigInt::from(core::u64::MAX);
+
+        let sum = add(a, b);
+
+        assert!(false, "{:#?} should have inner equal to {:?}", sum, core::u64::MAX as u128 + core::u64::MAX as u128);
+    } */
 }