如何从二进制文件中读取bitN整数数据？ [英] How to read bitN integer data from a binary file?
问题描述
我有一个由硬件生成的数据文件。一些数据是4位宽，一些是12位宽。 Matlab能够使用fread（fp，1，'ubit4 => uint16'）处理这些数据。我试图在C ++中做，但似乎没有简单的方法。我可以通过byte / int / long / long long读取，然后提取出请求的位。但它似乎无效率处理数百兆字节数据。
I have a data file generated by hardware. Some data is 4 bit wide and some is 12 bit wide. Matlab is able to process these data using fread(fp,1,'ubit4=>uint16'). I tried to do it in C++, but it seems that there is no simple way. I can read by byte/int/long/long long and then extract out the requested bits. but it seems inefficient dealing with hundreds mega bytes data.
要概括这个问题，问题是如何读取bitN整数（N从1到64例如）？任何人都可以推荐一个好的方式来从c ++中的文件中读取这种数据？
To generalize this problem, the question is how to read bitN integer (N from 1 to 64 for example)? Can anyone recommend a good way to read this kind of data from file in c++?
推荐答案
谢谢大家的贡献的答案，他们都非常有帮助。我不是想回答我的问题，得到的信用，但我觉得我有义务提供我的反馈在这个问题的进展。所有的学分都是上面的答案。
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.
为了实现matlab fread读取bitN整数的类似功能，我觉得模板类不合适，所以我来了
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.
我的想法是：我复制几个字节（从2到8字节）到我的对象并处理这些字节，并保持未处理的字节用于下一个处理。这里是我的代码和测试结果（仅实现<8bit的情况）：
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):
#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;
}
测试结果：
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
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