Work in terms of the number of bits to be handled.

Numeric/BitStream.hpp

@@ -14,13 +14,25 @@
 
 namespace Numeric {
 
-template <typename MaxIntT, bool lsb_first>
+/*!
+	Given a means to fetch the next byte from a byte stream, serialises those bytes into a bit stream.
+
+	@c max_bits is the largest number of bits that'll be read at once.
+	@c lsb_first if true then the LSB of each byte from the byte stream is the first bit read. Otherwise it's the MSB.
+*/
+template <int max_bits, bool lsb_first>
 class BitStream {
 public:
+	using IntT = min_int_size_t<max_bits + 8>;
+
 	BitStream(std::function<uint8_t(void)> next_byte) : next_byte_(next_byte) {}
 
+	/// @returns An integer composed of the next n bits of the bitstream where n is:
+	/// * the template parameter `bits` if it is non-zero; or
+	/// * the function argument `rbits` otherwise.
+	/// `rbits` is ignored if `bits` is non-zero.
 	template <size_t bits = 0>
-	MaxIntT next(size_t rbits = 0) {
+	IntT next([[maybe_unused]] const size_t rbits = 0) {
 		const size_t required = bits ? bits : rbits;
 		while(enqueued_ < required) {
 			uint8_t next = next_byte_();
@@ -28,11 +40,11 @@ public:
 				next = bit_reverse(next);
 			}
 
-			input_ |= ShiftT(next) << (BitSize - 8 - enqueued_);
+			input_ |= IntT(next) << (BitSize - 8 - enqueued_);
 			enqueued_ += 8;
 		}
 
-		const auto result = MaxIntT(input_ >> (BitSize - required));
+		const auto result = IntT(input_ >> (BitSize - required));
 		input_ <<= required;
 		enqueued_ -= required;
 		return result;
@@ -43,9 +55,8 @@ private:
 
 	size_t enqueued_{};
 
-	using ShiftT = uint_t<sizeof(MaxIntT) * 8 * 2>;
-	ShiftT input_{};
-	static constexpr size_t BitSize = sizeof(ShiftT) * 8;
+	IntT input_{};
+	static constexpr size_t BitSize = sizeof(IntT) * 8;
 };
 
 }

Numeric/Sizes.hpp

@@ -22,14 +22,15 @@ template <> struct uint_t_impl<64> { using type = uint64_t; };
 template <int size> using uint_t = typename uint_t_impl<size>::type;
 
 /*!
-	Maps to the smallest integral type that can contain max_value, from the following options:
+	Maps to the smallest integral type that can contain `max_value`, from the following options:
 
 	* uint8_t;
 	* uint16_t;
 	* uint32_t; or
 	* uint64_t.
 */
-template <uint64_t max_value> struct MinIntTypeValue {
+template <uint64_t max_value>
+struct MinIntTypeValue {
 	using type =
 		std::conditional_t<
 			max_value <= std::numeric_limits<uint8_t>::max(), uint8_t,
@@ -42,3 +43,29 @@ template <uint64_t max_value> struct MinIntTypeValue {
 			>
 		>;
 };
+template <uint64_t max_value> using min_int_value_t = typename MinIntTypeValue<max_value>::type;
+
+/*!
+	Maps to the smallest integral type that can hold at least `max_bits` bits, from the following options:
+
+	* uint8_t;
+	* uint16_t;
+	* uint32_t; or
+	* uint64_t.
+*/
+template <int max_bits>
+struct MinIntTypeSize {
+	static_assert(max_bits <= 64, "Only integers up to 64 bits are supported");
+	using type =
+		std::conditional_t<
+			max_bits <= 8, uint8_t,
+			std::conditional_t<
+				max_bits <= 16, uint16_t,
+				std::conditional_t<
+					max_bits <= 32, uint32_t,
+					uint64_t
+				>
+			>
+		>;
+};
+template <uint64_t max_value> using min_int_size_t = typename MinIntTypeValue<max_value>::type;

Storage/FileHolder.hpp

@@ -139,9 +139,9 @@ public:
 	/*!
 		Obtains a BitStream for reading from the file from the current reading cursor.
 	*/
-	template <typename MaxIntT, bool lsb_first>
-	Numeric::BitStream<MaxIntT, lsb_first> bitstream() {
-		return Numeric::BitStream<MaxIntT, lsb_first>([&] {
+	template <int max_bits, bool lsb_first>
+	Numeric::BitStream<max_bits, lsb_first> bitstream() {
+		return Numeric::BitStream<max_bits, lsb_first>([&] {
 			return get8();
 		});
 	}

Storage/Tape/Formats/TZX.cpp

@@ -178,7 +178,7 @@ void TZX::Serialiser::get_generalised_segment(
 	}
 
 	// Hence produce the output.
-	auto stream = file_.bitstream<uint8_t, false>();
+	auto stream = file_.bitstream<8, false>();
 	int base = 2;
 	size_t bits = 1;
 	while(base < number_of_symbols) {