[wihansaem1991]

BoxedUint::from_str_radix_vartime() strips leading zeros before decoding, so an input that is zero ("0", "00", "+0") leaves no digits and the result has no limbs at all:

let n = BoxedUint::from_str_radix_vartime("0", 10).unwrap();
assert_eq!(n.as_limbs().len(), 0);          // BoxedUint::zero() has 1 limb
assert_eq!(n.to_string_radix_vartime(10), ""); // docs say a zero value gives "0"
n.bits_vartime();                            // panics: index out of bounds (ref_type/bits.rs:68)

This returns BoxedUint::zero() when no digits are left. from_str_radix_with_precision_vartime() and the byte-slice constructors already produce at least one limb, so only this path changes.

The new from_str_radix_zero test covers "0", "00", "+0" and "0_0" in radix 2, 10, 16 and 36; it panics without the change. cargo test --features alloc --lib uint::boxed::encoding (release and debug), cargo clippy --all-targets --all-features -- -D warnings and cargo fmt --all -- --check pass.

This was found by differential fuzzing against num-bigint and fixed with an AI assistant (Claude Code), which also ran the checks above.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Sjtw7YxFWFKBH5rRZfwi9T

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.44%. Comparing base (c945e98) to head (b832f6d).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1382      +/-   ##
==========================================
+ Coverage   91.37%   91.44%   +0.06%     
==========================================
  Files         190      190              
  Lines       23201    23207       +6     
==========================================
+ Hits        21201    21222      +21     
+ Misses       2000     1985      -15     

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