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copied!<p>Thank you all for the contributed answers and they are all very helpful. I am not trying to answer my question and get the credit, but I feel I am obligated to give my feedback on the progress on this question. All credits goes to the above answers.</p> <p>To achieve the similar function of the matlab fread to read bitN integers, I feel that the template class is not proper, so I came up several functions to deal with <8bit <16bit <32bit and <64bit cases and process them separately.</p> <p>My idea is: I copy several bytes (from 2 to 8 bytes) to my object and process these bytes and keep unprocessed byte for next processing. Here is my code and testing results (only the <8bit case is implemented):</p> <pre><code>#include <math.h> #include <memory.h> typedef unsigned _int8 _uint8; typedef unsigned _int16 _uint16; typedef unsigned _int32 _uint32; typedef unsigned _int64 _uint64; class bitbuffer { _uint8 *pbuf; _uint8 *pelem; //can be casted to int16/32/64 _uint32 pbuf_len; //buf length in byte _uint32 pelem_len; //element length in byte union membuf { _uint64 buf64; _uint32 buf32; _uint16 buf16; _uint8 buf8[2]; } tbuf; //bookkeeping information _uint8 start_bit; // _uint32 byte_pos; //current byte position _uint32 elem_pos; public: bitbuffer(_uint8 *src,_uint32 src_len,_uint8 *dst,_uint32 dst_len) { pbuf=src;pelem=dst; pbuf_len=src_len;pelem_len=dst_len; start_bit=0;byte_pos=0;elem_pos=0; } //to define the source and destination void set_startbit(_uint8 bit) {start_bit=bit;} void set_bytepos(_uint32 pos) {byte_pos=pos;} void set_elempos(_uint32 pos) {elem_pos=pos;} void reset() {start_bit=0;byte_pos=0;elem_pos=0;} //for restart something from somewhere else //OUT getbits(IN a, _uint8 nbits); //get nbits from a using start and byte_pos _uint32 get_elem_uint8(_uint32 num_elem,_uint8 nbits) //output limit to 8/16/32/64 only { _uint32 num_read=0; _uint16 mask=pow(2,nbits)-1;//00000111 for example nbit=3 while(byte_pos<=pbuf_len-2) { //memcpy((char*)&tbuf.buf16,pbuf+byte_pos,2); //copy 2 bytes into our buffer, this may introduce redundant copy tbuf.buf8[1]=pbuf[byte_pos]; //for little endian machine, swap the bytes tbuf.buf8[0]=pbuf[byte_pos+1]; //now we have start_bits, byte_pos, elem_pos, just finish them all while(start_bit<=16-nbits) { pelem[elem_pos++]=(tbuf.buf16>>(16-start_bit-nbits))&mask;//(tbuf.buf16&(mask<<(16-start_bit)) start_bit+=nbits; //advance by nbits num_read++; if(num_read>=num_elem) { break; } } //need update the start_bit and byte_pos byte_pos+=(start_bit/8); start_bit%=8; if(num_read>=num_elem) { break; } } return num_read; } /* _uint32 get_elem_uint16(_uint32 num_elem,_uint8 nbits) //output limit to 8/16/32/64 only { _uint32 num_read=0; _uint32 mask=pow(2,nbits)-1;//00000111 for example nbit=3 while(byte_pos<pbuf_len-4) { memcpy((char*)&tbuf.buf32,pbuf+byte_pos,4); //copy 2 bytes into our buffer, this may introduce redundant copy //now we have start_bits, byte_pos, elem_pos, just finish them all while(start_bit<=32-nbits) { pelem[elem_pos++]=(tbuf.buf32>>(32-start_bit-nbits))&mask;//(tbuf.buf16&(mask<<(16-start_bit)) start_bit+=nbits; //advance by nbits num_read++; if(num_read>=num_elem) { break; } } //need update the start_bit and byte_pos start_bit%=8; byte_pos+=(start_bit/8); if(num_read>=num_elem) { break; } } return num_read; } _uint32 get_elem_uint32(_uint32 num_elem,_uint8 nbits) //output limit to 8/16/32/64 only { _uint32 num_read=0; _uint64 mask=pow(2,nbits)-1;//00000111 for example nbit=3 while(byte_pos<pbuf_len-8) { memcpy((char*)&tbuf.buf16,pbuf+byte_pos,8); //copy 2 bytes into our buffer, this may introduce redundant copy //now we have start_bits, byte_pos, elem_pos, just finish them all while(start_bit<=64-nbits) { pelem[elem_pos++]=(tbuf.buf64>>(64-start_bit-nbits))&mask;//(tbuf.buf16&(mask<<(16-start_bit)) start_bit+=nbits; //advance by nbits num_read++; if(num_read>=num_elem) { break; } } //need update the start_bit and byte_pos start_bit%=8; byte_pos+=(start_bit/8); if(num_read>=num_elem) { break; } } return num_read; } //not work well for 64 bit! _uint64 get_elem_uint64(_uint32 num_elem,_uint8 nbits) //output limit to 8/16/32/64 only { _uint32 num_read=0; _uint64 mask=pow(2,nbits)-1;//00000111 for example nbit=3 while(byte_pos<pbuf_len-2) { memcpy((char*)&tbuf.buf16,pbuf+byte_pos,8); //copy 2 bytes into our buffer, this may introduce redundant copy //now we have start_bits, byte_pos, elem_pos, just finish them all while(start_bit<=16-nbits) { pelem[elem_pos++]=(tbuf.buf16>>(16-start_bit-nbits))&mask;//(tbuf.buf16&(mask<<(16-start_bit)) start_bit+=nbits; //advance by nbits num_read++; if(num_read>=num_elem) { break; } } //need update the start_bit and byte_pos start_bit%=8; byte_pos+=(start_bit/8); if(num_read>=num_elem) { break; } } return num_read; }*/ }; #include <iostream> using namespace std; int main() { _uint8 *pbuf=new _uint8[10]; _uint8 *pelem=new _uint8[80]; for(int i=0;i<10;i++) pbuf[i]=i*11+11; bitbuffer vbit(pbuf,10,pelem,10); cout.setf(ios_base::hex,ios_base::basefield); cout<<"Bytes: "; for(i=0;i<10;i++) cout<<pbuf[i]<<" "; cout<<endl; cout<<"1 bit: "; int num_read=vbit.get_elem_uint8(80,1); for(i=0;i<num_read;i++) cout<<(int)pelem[i]; cout<<endl; vbit.reset(); cout<<"2 bit: "; num_read=vbit.get_elem_uint8(40,2); for(i=0;i<num_read;i++) cout<<(int)pelem[i]<<" "; cout<<endl; vbit.reset(); cout<<"3 bit: "; num_read=vbit.get_elem_uint8(26,3); for(i=0;i<num_read;i++) cout<<(int)pelem[i]<<' '; cout<<endl; vbit.reset(); cout<<"4 bit: "; num_read=vbit.get_elem_uint8(20,4);//get 10 bit-12 integers for(i=0;i<num_read;i++) cout<<(int)pelem[i]<<" "; cout<<endl; vbit.reset(); cout<<"5 bit: "; num_read=vbit.get_elem_uint8(16,5);//get 10 bit-12 integers for(i=0;i<num_read;i++) cout<<(int)pelem[i]<<" "; cout<<endl; vbit.reset(); cout<<"6 bit: "; num_read=vbit.get_elem_uint8(13,6);//get 10 bit-12 integers for(i=0;i<num_read;i++) cout<<(int)pelem[i]<<" "; cout<<endl; vbit.reset(); cout<<"7 bit: "; num_read=vbit.get_elem_uint8(11,7);//get 10 bit-12 integers for(i=0;i<num_read;i++) cout<<(int)pelem[i]<<" "; cout<<endl; vbit.reset(); cout<<"8 bit: "; num_read=vbit.get_elem_uint8(10,8);//get 10 bit-12 integers for(i=0;i<num_read;i++) cout<<(int)pelem[i]<<" "; cout<<endl; vbit.reset(); return 0; } </code></pre> <p>testing results:</p> <pre><code>Bytes: b 16 21 2c 37 42 4d 58 63 6e 1 bit: 0000101100010110001000010010110000110111010000100100110101011000011000110 1101110 2 bit: 0 0 2 3 0 1 1 2 0 2 0 1 0 2 3 0 0 3 1 3 1 0 0 2 1 0 3 1 1 1 2 0 1 2 0 3 1 2 3 2 3 bit: 0 2 6 1 3 0 4 1 1 3 0 3 3 5 0 2 2 3 2 5 4 1 4 3 4 bit: 0 b 1 6 2 1 2 c 3 7 4 2 4 d 5 8 6 3 6 e 5 bit: 1 c b 2 2 b 1 17 8 9 6 15 10 18 1b e 6 bit: 2 31 18 21 b 3 1d 2 13 15 21 23 7 bit: 5 45 44 12 61 5d 4 4d 2c 18 6d 8 bit: b 16 21 2c 37 42 4d 58 63 6e Press any key to continue </code></pre>

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