[libc] Allow BigInt class to use base word types other than uint64_t. (#81634)

This will allow DyadicFloat class to replace NormalFloat class.

Author: lntue

libc/src/__support/FPUtil/dyadic_float.h

@@ -216,7 +216,7 @@ constexpr DyadicFloat<Bits> quick_add(DyadicFloat<Bits> a,
     if (result.mantissa.add(b.mantissa)) {
       // Mantissa addition overflow.
       result.shift_right(1);
-      result.mantissa.val[DyadicFloat<Bits>::MantissaType::WORDCOUNT - 1] |=
+      result.mantissa.val[DyadicFloat<Bits>::MantissaType::WORD_COUNT - 1] |=
           (uint64_t(1) << 63);
     }
     // Result is already normalized.
@@ -243,7 +243,7 @@ constexpr DyadicFloat<Bits> quick_add(DyadicFloat<Bits> a,
 //   result.mantissa = quick_mul_hi(a.mantissa + b.mantissa)
 //                   ~ (full product a.mantissa * b.mantissa) >> Bits.
 // The errors compared to the mathematical product is bounded by:
-//   2 * errors of quick_mul_hi = 2 * (UInt<Bits>::WORDCOUNT - 1) in ULPs.
+//   2 * errors of quick_mul_hi = 2 * (UInt<Bits>::WORD_COUNT - 1) in ULPs.
 // Assume inputs are normalized (by constructors or other functions) so that we
 // don't need to normalize the inputs again in this function.  If the inputs are
 // not normalized, the results might lose precision significantly.
@@ -258,7 +258,7 @@ constexpr DyadicFloat<Bits> quick_mul(DyadicFloat<Bits> a,
     result.mantissa = a.mantissa.quick_mul_hi(b.mantissa);
     // Check the leading bit directly, should be faster than using clz in
     // normalize().
-    if (result.mantissa.val[DyadicFloat<Bits>::MantissaType::WORDCOUNT - 1] >>
+    if (result.mantissa.val[DyadicFloat<Bits>::MantissaType::WORD_COUNT - 1] >>
             63 ==
         0)
       result.shift_left(1);