From f99a9c20df6a1b634c7e7f877e103c24f3ee6d70 Mon Sep 17 00:00:00 2001
From: Andrew Guschin <guschin.drew@gmail.com>
Date: Fri, 3 Mar 2023 10:15:42 +0400
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---
 sem2/src/mpn.rs | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 52 insertions(+), 1 deletion(-)

(limited to 'sem2/src/mpn.rs')

diff --git a/sem2/src/mpn.rs b/sem2/src/mpn.rs
index ecc1d5c..24880ca 100644
--- a/sem2/src/mpn.rs
+++ b/sem2/src/mpn.rs
@@ -1,6 +1,6 @@
 use std::cmp::max;
 use std::fmt;
-use std::ops::Add;
+use std::ops::{Add, Sub};
 
 pub struct Number {
     radix: usize,
@@ -41,6 +41,21 @@ impl Number {
             None
         }
     }
+
+    fn fix_leading_zeros(mut self) -> Self {
+        let mut leading = 0;
+        for i in (1..self.digits.len()).rev() {
+            if self.digits[i] == 0 {
+                leading += 1;
+            } else {
+                break;
+            }
+        }
+        for _ in 0..leading {
+            self.digits.pop();
+        }
+        return self;
+    }
 }
 
 impl fmt::Display for Number {
@@ -92,3 +107,39 @@ impl Add for Number {
         };
     }
 }
+
+impl Sub for Number {
+    type Output = Self;
+
+    fn sub(self, other: Self) -> Self::Output {
+        let len = max(self.len(), other.len());
+        let mut digits = Vec::new();
+        let mut k = 0;
+        for i in 0..len {
+            let q1 = if i < self.len() {
+                self.digits[i] as i64
+            } else {
+                0_i64
+            };
+            let q2 = if i < other.len() {
+                other.digits[i] as i64
+            } else {
+                0_i64
+            };
+            let b = self.radix as i64;
+            let res = q1 - q2 + k;
+            let digit = (res + b) % b;
+            k = if res < 0 { -1 } else { 0 };
+            digits.push(digit as u8);
+        }
+        if k != 0 {
+            digits.push(k as u8);
+        }
+
+        return Number {
+            radix: self.radix,
+            digits,
+        }
+        .fix_leading_zeros();
+    }
+}
-- 
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