split out remove_zero_from_interval

Author: programmerjake

src/algebraic_numbers.rs

@@ -623,35 +623,43 @@ impl RealAlgebraicNumber {
     pub fn trunc(&self) -> Self {
         self.to_integer_trunc().into()
     }
-    pub fn checked_recip(&self) -> Option<Self> {
-        if let Some(value) = self.to_rational() {
-            if value.is_zero() {
-                return None;
-            }
-            return Some(value.recip().into());
-        }
+    /// shrinks the interval till it doesn't contain zero
+    #[must_use]
+    fn remove_zero_from_interval(&mut self) -> Option<(Sign, IntervalShrinker)> {
         let sign = match self.cmp_with_zero() {
-            Ordering::Equal => unreachable!("already checked for zero"),
+            Ordering::Equal => return None,
             Ordering::Less => Sign::Negative,
             Ordering::Greater => Sign::Positive,
         };
-        let mut value = self.clone();
         match sign {
             Sign::Negative => {
-                if value.interval().upper_bound_numer().is_positive() {
-                    value.data.interval.set_upper_bound_to_zero();
+                if self.interval().upper_bound_numer().is_positive() {
+                    self.data.interval.set_upper_bound_to_zero();
                 }
             }
             Sign::Positive => {
-                if value.interval().lower_bound_numer().is_negative() {
-                    value.data.interval.set_lower_bound_to_zero();
+                if self.interval().lower_bound_numer().is_negative() {
+                    self.data.interval.set_lower_bound_to_zero();
                 }
             }
         }
-        let mut interval_shrinker = value.interval_shrinker();
+        let mut interval_shrinker = self.interval_shrinker();
         while interval_shrinker.interval.contains_zero() {
             interval_shrinker.shrink();
         }
+        Some((sign, interval_shrinker))
+    }
+    pub fn checked_recip(&self) -> Option<Self> {
+        if let Some(value) = self.to_rational() {
+            if value.is_zero() {
+                return None;
+            }
+            return Some(value.recip().into());
+        }
+        let mut value = self.clone();
+        value
+            .remove_zero_from_interval()
+            .expect("known to be non-zero");
         let RealAlgebraicNumberData {
             minimal_polynomial,
             interval,