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

[via llvm-commits]

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@@ -559,57 +566,17 @@ struct BigInt {
   // That is by truncating the fractionnal part
   // https://stackoverflow.com/a/3602857
   LIBC_INLINE constexpr cpp::optional<BigInt> div(const BigInt &divider) {
-    auto &dividend = *this;
-    if constexpr (SIGNED) {
-      // Signed Multiword Division
-      // 1. Negate the dividend it it is negative, and similarly for the
-      // divisor.
-      // 2. Convert the divident and divisor to unsigned representation.
-      // 3. Use unsigned multiword division algorithm.
-      // 4. Convert the quotient and remainder to signed representation.
-      // 5. Negate the quotient if the dividend and divisor had opposite signs.
-      // 6. Negate the remainder if the dividend was negative.
-      const bool dividend_is_neg = dividend.is_neg();
-      const bool divider_is_neg = divider.is_neg();
-      unsigned_type udividend(dividend);
-      unsigned_type udivider(divider);
-      if (dividend_is_neg)
-        udividend.negate();
-      if (divider_is_neg)
-        udivider.negate();
-      auto maybe_remainder = udividend.div(udivider);
-      if (!maybe_remainder)
-        return cpp::nullopt;
-      unsigned_type remainder = *maybe_remainder;
-      if (dividend_is_neg != divider_is_neg)
-        udividend.negate(); // this is the quotient
-      dividend = signed_type(udividend);
-      if (dividend_is_neg)
-        remainder.negate();
-      return signed_type(remainder);
-    } else {
-      BigInt remainder;
-      if (divider.is_zero())
-        return cpp::nullopt;
-      if (divider == 1)
-        return remainder;
-      BigInt quotient;
-      if (dividend >= divider) {
-        BigInt subtractor = divider;
-        int cur_bit = multiword::countl_zero(subtractor.val) -
-                      multiword::countl_zero(dividend.val);
-        subtractor <<= cur_bit;
-        for (; cur_bit >= 0 && dividend > 0; --cur_bit, subtractor >>= 1) {
-          if (dividend < subtractor)
-            continue;
-          dividend -= subtractor;
-          quotient.set_bit(cur_bit);
-        }
-      }
-      remainder = dividend;
-      dividend = quotient;
-      return remainder;
-    }
+    if (divider.is_zero())
+      return cpp::nullopt;
+    if (divider == 1)
----------------
lntue wrote:

Do you want to use `LIBC_UNLIKELY` to provide hints for these 2 cases?

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