[util] Add helpers to encode or decode fixed-point numbers

src/util/util_bit.h

@@ -529,4 +529,61 @@ namespace dxvk::bit {
     uint32_t m_mask;
 
   };
+
+
+  /**
+   * \brief Encodes float as fixed point
+   *
+   * Rounds away from zero. If this is not suitable for
+   * certain use cases, implement round to nearest even.
+   * \tparam T Integer type, may be signed
+   * \tparam I Integer bits
+   * \tparam F Fractional bits
+   * \param n Float to encode
+   * \returns Encoded fixed-point value
+   */
+  template<typename T, int32_t I, int32_t F>
+  T encodeFixed(float n) {
+    if (n != n)
+      return 0u;
+
+    n *= float(1u << F);
+
+    if constexpr (std::is_signed_v<T>) {
+      n = std::max(n, -float(1u << (I + F - 1u)));
+      n = std::min(n,  float(1u << (I + F - 1u)) - 1.0f);
+      n += n < 0.0f ? -0.5f : 0.5f;
+    } else {
+      n = std::max(n, 0.0f);
+      n = std::min(n, float(1u << (I + F)) - 1.0f);
+      n += 0.5f;
+    }
+
+    T result = T(n);
+
+    if constexpr (std::is_signed_v<T>)
+      result &= ((T(1u) << (I + F)) - 1u);
+
+    return result;
+  }
+
+
+  /**
+   * \brief Decodes fixed-point integer to float
+   *
+   * \tparam T Integer type, may be signed
+   * \tparam I Integer bits
+   * \tparam F Fractional bits
+   * \param n Number to decode
+   * \returns Decoded  number
+   */
+  template<typename T, int32_t I, int32_t F>
+  float decodeFixed(T n) {
+    // Sign-extend as necessary
+    if constexpr (std::is_signed_v<T>)
+      n -= (n & (T(1u) << (I + F - 1u))) << 1u;
+
+    return float(n) / float(1u << F);
+  }
+
 }