[libc-commits] [libc] [libc] add FXBits class (PR #82065)

[Guillaume Chatelet via libc-commits]

================
@@ -19,6 +21,74 @@
 
 namespace LIBC_NAMESPACE::fixed_point {
 
+template <typename T> struct FXBits {
+private:
+  using fx_rep = FXRep<T>;
+  using StorageType = typename fx_rep::StorageType;
+
+  StorageType value;
+
+  static_assert(fx_rep::FRACTION_LEN > 0);
+
+  static constexpr size_t FRACTION_OFFSET = 0; // Just for completeness
+  static constexpr size_t INTEGRAL_OFFSET = fx_rep::FRACTION_LEN;
+  static constexpr size_t SIGN_OFFSET =
+      fx_rep::SIGN_LEN == 0
+          ? 0
+          : ((sizeof(StorageType) * CHAR_BIT) - fx_rep::SIGN_LEN);
+
+  static constexpr StorageType FRACTION_MASK =
+      (StorageType(1) << fx_rep::FRACTION_LEN) - 1;
+  static constexpr StorageType INTEGRAL_MASK =
+      ((StorageType(1) << fx_rep::INTEGRAL_LEN) - 1) << INTEGRAL_OFFSET;
+  static constexpr StorageType SIGN_MASK =
+      (fx_rep::SIGN_LEN == 0 ? 0 : StorageType(1) << SIGN_OFFSET);
+
+public:
+  LIBC_INLINE constexpr FXBits() = default;
+
+  template <typename XType> LIBC_INLINE constexpr explicit FXBits(XType x) {
+    using Unqual = typename cpp::remove_cv_t<XType>;
+    if constexpr (cpp::is_same_v<Unqual, T>) {
+      value = cpp::bit_cast<StorageType>(x);
+    } else if constexpr (cpp::is_same_v<Unqual, StorageType>) {
+      value = x;
+    } else {
+      // We don't want accidental type promotions/conversions, so we require
+      // exact type match.
+      static_assert(cpp::always_false<XType>);
+    }
+  }
+
+  LIBC_INLINE constexpr StorageType get_fraction() {
+    return (value & FRACTION_MASK) >> FRACTION_OFFSET;
+  }
+
+  LIBC_INLINE constexpr StorageType get_integral() {
+    return (value & INTEGRAL_MASK) >> INTEGRAL_OFFSET;
+  }
+
+  LIBC_INLINE constexpr StorageType get_sign() {
+    return (value & SIGN_MASK) >> SIGN_OFFSET;
+  }
+
+  LIBC_INLINE constexpr void set_fraction(StorageType fraction) {
+    value = (value & (~FRACTION_MASK)) |
+            ((fraction << FRACTION_OFFSET) & FRACTION_MASK);
+  }
+
+  LIBC_INLINE constexpr void set_integral(StorageType integral) {
+    value = (value & (~INTEGRAL_MASK)) |
+            ((integral << INTEGRAL_OFFSET) & INTEGRAL_MASK);
+  }
+
+  LIBC_INLINE constexpr void set_sign(StorageType sign) {
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gchatelet wrote:

I think it's indeed the right time to extract `Sign` and make it a first class citizen in LLVM libc.

https://github.com/llvm/llvm-project/pull/82065