From d90b76275459d8561667a48c433620558a5128a2 Mon Sep 17 00:00:00 2001
From: Timothy Warren <twarren@nabancard.com>
Date: Fri, 11 Sep 2020 15:23:42 -0400
Subject: [PATCH] Implement Bigint from implementation for integer types larger
 than the pointer type

---
 src/bigint.rs | 84 +++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 71 insertions(+), 13 deletions(-)

diff --git a/src/bigint.rs b/src/bigint.rs
index a7af4c9..be85e9e 100644
--- a/src/bigint.rs
+++ b/src/bigint.rs
@@ -14,7 +14,7 @@ use alloc::string::*;
 use std::prelude::v1::*;
 
 use core::cmp::{Ordering, PartialOrd, PartialEq};
-use core::convert::TryInto;
+use core::convert::*;
 use core::mem::replace;
 use core::ops::{
     Add, AddAssign, Div, DivAssign, Mul, MulAssign, Neg, Not, Rem, RemAssign, Sub, SubAssign,
@@ -465,7 +465,36 @@ macro_rules! impl_from_larger {
             impl From<$s> for BigInt {
                 /// Create a `BigInt` from a signed integer primitive
                 fn from(n: $s) -> Self {
-                    todo!();
+                    use core::usize::MAX;
+                    let target_radix: $s = (MAX as $s) + 1;
+                    let sign = if n < 0 { Sign::Negative } else { Sign::Positive };
+                    let n = n.abs();
+
+                    let mut quotient = n / target_radix;
+                    let mut rem = n % target_radix;
+
+                    if quotient == 0 {
+                        Self::from(rem as usize)
+                    } else {
+                        let mut inner: Vec<usize> = Vec::new();
+                        inner.push(rem as usize);
+
+                        loop {
+                            rem = quotient % target_radix;
+                            quotient = quotient / target_radix;
+
+                            inner.push(rem as usize);
+
+                            if (quotient == 0) {
+                                break;
+                            }
+                        }
+
+                        BigInt {
+                            inner,
+                            sign,
+                        }
+                    }
                 }
             }
 
@@ -473,14 +502,32 @@ macro_rules! impl_from_larger {
                 /// Create a `BigInt` from an unsigned integer primitive
                 fn from(n: $u) -> Self {
                     use core::usize::MAX;
+                    let target_radix: $u = (MAX as $u) + 1;
 
-                    let base_usize_value = n / MAX as $u;
-                    let rem = n % MAX as $u;
+                    let mut quotient = n / target_radix;
+                    let mut rem = n % target_radix;
 
-                    if base_usize_value == 0 {
+                    if quotient == 0 {
                         Self::from(rem as usize)
                     } else {
-                        todo!();
+                        let mut inner: Vec<usize> = Vec::new();
+                        inner.push(rem as usize);
+
+                        loop {
+                            rem = quotient % target_radix;
+                            quotient = quotient / target_radix;
+
+                            inner.push(rem as usize);
+
+                            if (quotient == 0) {
+                                break;
+                            }
+                        }
+
+                        BigInt {
+                            inner,
+                            sign: Sign::Positive
+                        }
                     }
                 }
             }
@@ -536,6 +583,9 @@ impl_ord_literal!(i8,u8,i16,u16,i32,u32,i64,u64,i128,u128);
 mod tests {
     use super::*;
 
+    const RADIX: u128 = core::usize::MAX as u128 + 1;
+    const I_RADIX: i128 = core::usize::MAX as i128 + 1;
+
     #[test]
     fn sanity_checks() {
         let int = BigInt::from(45u8);
@@ -555,14 +605,14 @@ mod tests {
 
     #[test]
     fn test_trim_zeros() {
-        let mut lotsoftrailing = BigInt {
+        let mut lots_of_leading = BigInt {
             inner: vec![1, 0, 0, 0, 0, 0, 0, 0, 0],
             sign: Positive,
         };
 
-        lotsoftrailing.trim_zeros();
+        lots_of_leading.trim_zeros();
 
-        assert_eq!(BigInt::from(1), lotsoftrailing);
+        assert_eq!(BigInt::from(1), lots_of_leading);
     }
 
     #[test]
@@ -815,15 +865,23 @@ mod tests {
     }
 
     #[test]
-    #[should_panic]
     fn test_from_large_unsigned() {
-        BigInt::from(core::u128::MAX);
+        let big_num: u128 = 9*RADIX + 8;
+        let res = BigInt::from(big_num);
+
+        assert_eq!(res.sign, Sign::Positive, "{:#?}", res);
+        assert_eq!(res.inner[0], 8usize, "{:#?}", res);
+        assert_eq!(res.inner[1], 9usize, "{:#?}", res);
     }
 
     #[test]
-    #[should_panic]
     fn test_from_large_signed() {
-        BigInt::from(128i128);
+        let big_num: i128 = 2*I_RADIX + 3;
+        let res = BigInt::from(-big_num);
+
+        assert_eq!(res.sign, Sign::Negative, "{:#?}", res);
+        assert_eq!(res.inner[0], 3usize, "{:#?}", res);
+        assert_eq!(res.inner[1], 2usize, "{:#?}", res);
     }
 
     #[test]