121 lines
3.8 KiB
C++
121 lines
3.8 KiB
C++
#include <iostream>
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#include <bitset>
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#include "bitstream.h"
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#define min(x,y) (((x) > (y)) ? (y) : (x))
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// i.e when stream is 0b12345678 0bABCDEFGH and command is
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// to read 12 bits:
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// out = 00000000 00000000 00008765 4321HGFE
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// to read 2 bits:
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// out = 00000000 00000000 00000000 00000087
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int ibitstream::getbits(size_t n) {
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// std::cerr << "To read " << n << " count: " << this->count << " " << this->cache << std::endl;
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int out = 0, read = 0, to_read;
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if (n > 32 || n < 0) {
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throw std::runtime_error("When reading bits from bitstream n must be <= 32");
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}
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// read to cache
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if (this->count == -1 || this->count >= 8) {
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if (!(this->is >> cache)) throw std::runtime_error("Stream EOF");
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this->count = 0;
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}
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while (n > 0) {
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to_read = min(n, 8 - this->count);
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// std::cerr << "Iter n: " << n << " count: " << this->count << " "
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// << this->cache << " to_read: " << to_read << " already read: " << read << std::endl;
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// cache & 0b11111000 if count = 3;
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// cache & 0b10000000 if count = 7;
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// cache & 0b11111111 if count = 0, etc;
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uint8_t mask = (((1 << to_read) - 1) << this->count);
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uint8_t chunk = ((cache & mask) >> this->count);
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// todo inverse chunk
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uint8_t inv = 0;
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for (size_t i = 0; i < to_read; i++)
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{
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inv |= ((chunk >> i) & 1) << (to_read - i - 1);
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}
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out <<= to_read; // shift by length of chunk
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out |= inv; // concat with chunk
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// out |= inv << read;
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// std::cerr << "Mask " << std::bitset<8>(mask) << " chunk " << std::bitset<8>(chunk) <<
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// " inv " << std::bitset<8>(inv) << " out " << std::bitset<32>(out) << std::endl;
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this->count += to_read;
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// read += to_read;
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n -= to_read;
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if (this->count == 8){
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// read another byte
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if (!(this->is >> cache)) throw std::runtime_error("Stream EOF");
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this->count = 0;
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}
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}
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return out;
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}
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void obitstream::writebits(short bits, size_t n) {
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// std::cerr << "Write: " << std::bitset<16>(bits) << " n: " << n << " count: " << this->count << " cache: " << std::bitset<8>(this->cache) << std::endl;
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int written = 0, to_write;
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while (n > 0) {
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to_write = min(n, 8 - this->count);
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// mask:
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// ------- n -----------------------------
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// 00000..00000 1...1111111111 000000..000 == bits
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// - written - | - to_write - | - offset -
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// so offset = n - to_write
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// because n = n - to_write at every step, so written is already present
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uint16_t mask = (((1 << to_write) - 1) << (n - to_write));
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uint8_t chunk = (bits & mask) >> (n - to_write);
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// todo inverse bits in chunk
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uint8_t inv = 0;
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for (size_t i = 0; i < to_write; i++)
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{
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inv |= ((chunk >> i) & 1) << (to_write - i - 1);
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}
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// std::cerr << "Chunk " << std::bitset<8>(chunk) << " inv " << std::bitset<8>(inv) << " to_write "
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// << to_write << " written " << written << " n " << n << " mask " << std::bitset<16>(mask)
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// << " offset " << (n - to_write) << std::endl;
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this->cache |= (inv << this->count);
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this->count += to_write;
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written += to_write;
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n -= to_write;
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if (this->count == 8){
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// flush chunk
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// std::cerr << "Flush: " << std::bitset<8>(this->cache) << std::endl;
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os << this->cache;
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os.flush();
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this->count = 0;
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this->cache = 0;
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}
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}
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}
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void obitstream::flush() {
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// std::cerr << "Flush: " << std::bitset<8>(this->cache) << std::endl;
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os << this->cache;
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os.flush();
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this->cache = 0;
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this->count = 0;
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}
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