[libc] [llvm] [libc] Refactor `BigInt` (PR #86137)

[Nick Desaulniers via llvm-commits]

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@@ -169,6 +169,15 @@ LIBC_INLINE constexpr auto operator""_u256(const char *x) {
   return internal::parse_with_prefix<UInt<256>>(x);
 }
 
+template <typename T> LIBC_INLINE constexpr T parse_bigint(const char *x) {
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nickdesaulniers wrote:

Consider what happens when `x == nullptr` or `x == ""`. You don't use it currently that way, but you did put this function in __support; others may use it one day.

https://github.com/llvm/llvm-project/pull/86137