Merge pull request #445 from elichai/2020-07-divmod

Use the remainder from div_rem instead of recomputing it

src/util/uint.rs

@@ -84,6 +84,42 @@ macro_rules! construct_uint {
                 assert!(init >= 0);
                 $name::from_u64(init as u64)
             }
+
+            // divmod like operation, returns (quotient, remainder)
+            #[inline]
+            fn div_rem(self, other: Self) -> (Self, Self) {
+                let mut sub_copy = self;
+                let mut shift_copy = other;
+                let mut ret = [0u64; $n_words];
+
+                let my_bits = self.bits();
+                let your_bits = other.bits();
+
+                // Check for division by 0
+                assert!(your_bits != 0);
+
+                // Early return in case we are dividing by a larger number than us
+                if my_bits < your_bits {
+                    return ($name(ret), sub_copy);
+                }
+
+                // Bitwise long division
+                let mut shift = my_bits - your_bits;
+                shift_copy = shift_copy << shift;
+                loop {
+                    if sub_copy >= shift_copy {
+                        ret[shift / 64] |= 1 << (shift % 64);
+                        sub_copy = sub_copy - shift_copy;
+                    }
+                    shift_copy = shift_copy >> 1;
+                    if shift == 0 {
+                        break;
+                    }
+                    shift -= 1;
+                }
+
+                ($name(ret), sub_copy)
+            }
         }
 
         impl ::std::ops::Add<$name> for $name {
@@ -134,35 +170,7 @@ macro_rules! construct_uint {
             type Output = $name;
 
             fn div(self, other: $name) -> $name {
-                let mut sub_copy = self;
+                self.div_rem(other).0
-                let mut shift_copy = other;
-                let mut ret = [0u64; $n_words];
-        
-                let my_bits = self.bits();
-                let your_bits = other.bits();
-
-                // Check for division by 0
-                assert!(your_bits != 0);
-
-                // Early return in case we are dividing by a larger number than us
-                if my_bits < your_bits {
-                    return $name(ret);
-                }
-
-                // Bitwise long division
-                let mut shift = my_bits - your_bits;
-                shift_copy = shift_copy << shift;
-                loop {
-                    if sub_copy >= shift_copy {
-                        ret[shift / 64] |= 1 << (shift % 64);
-                        sub_copy = sub_copy - shift_copy;
-                    }
-                    shift_copy = shift_copy >> 1;
-                    if shift == 0 { break; }
-                    shift -= 1;
-                }
-
-                $name(ret)
             }
         }
 
@@ -170,8 +178,7 @@ macro_rules! construct_uint {
             type Output = $name;
 
             fn rem(self, other: $name) -> $name {
-                let times = self / other;
+                self.div_rem(other).1
-                self - (times * other)
             }
         }
 
@@ -568,4 +575,3 @@ mod tests {
         assert_eq!(end2.ok(), Some(start2));
     }
 }
-