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

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Thomas Harte
2025-02-19 22:04:51 -05:00
parent 6aff0b74cd
commit 88ffcbc62b
4 changed files with 51 additions and 13 deletions
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25
Numeric/BitStream.hpp
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@@ -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;
};
}