nth root - improved precondition check

Author: andrei-marinica

framework/base/src/types/managed/wrapped/managed_decimal.rs

@@ -17,7 +17,8 @@ pub use managed_decimal_signed::ManagedDecimalSigned;
 
 use crate::{
     abi::{TypeAbi, TypeAbiFrom, TypeName},
-    api::{ManagedTypeApi, ManagedTypeApiImpl},
+    api::{ManagedTypeApi, ManagedTypeApiImpl, quick_signal_error},
+    err_msg,
     formatter::{FormatBuffer, FormatByteReceiver, SCDisplay},
     typenum::{U4, U8, Unsigned},
     types::BigUint,
@@ -156,6 +157,10 @@ impl<M: ManagedTypeApi, D: Decimals + Clone> ManagedDecimal<M, D> {
     /// # Panics
     /// Panics if `k` is zero.
     pub fn nth_root(&self, k: u32) -> Self {
+        if k == 0 {
+            quick_signal_error::<M>(err_msg::BIG_UINT_NTH_ROOT_ZERO);
+        }
+
         if k == 1 {
             return self.clone();
         }
@@ -164,7 +169,7 @@ impl<M: ManagedTypeApi, D: Decimals + Clone> ManagedDecimal<M, D> {
         // Multiply by sf^(k-1) before rooting so the decimal position is preserved.
         // For k==0, the check in BigUint::nth_root handles the error signal.
         let scaled = &self.data * &sf.pow(k.saturating_sub(1));
-        ManagedDecimal::from_raw_units(scaled.nth_root(k), self.decimals.clone())
+        ManagedDecimal::from_raw_units(scaled.nth_root_unchecked(k), self.decimals.clone())
     }
 }
 

framework/base/src/types/managed/wrapped/num/big_uint.rs

@@ -364,6 +364,11 @@ impl<M: ManagedTypeApi> BigUint<M> {
             return self.clone();
         }
 
+        self.nth_root_unchecked(k)
+    }
+
+    // Expects k > 1. Does not check this precondition, so it is the caller's responsibility to ensure it.
+    pub(crate) fn nth_root_unchecked(&self, k: u32) -> Self {
         // log2 is None for the number zero,
         // but in this case we can return early with the correct result of zero without doing any computation
         let Some(log2) = self.log2_floor() else {