MATLAB代码实现getbitu函数

好的，以下是MATLAB代码实现getbitu函数的示例：

function bits = getbitu(buf, start, len)
%GETBITU Extract bits from a buffer
% buf: buffer containing binary data
% start: starting bit position
% len: length of bits to extract
%
% Returns the extracted bits as a decimal number

byte = floor(start / 8) + 1;
bit = 8 - mod(start, 8);
mask = bitcmp(0, 'uint8');
mask = bitshift(mask, bit - 1);

bits = 0;

for i = 1:len
    if bit == 8
        byte = byte + 1;
        bit = 1;
    else
        bit = bit + 1;
    end
    
    bits = bits * 2;
    if bitand(uint8(buf(byte)), mask)
        bits = bits + 1;
    end
    
    mask = bitshift(mask, 1);
    if bitshift(mask, -1) == 0
        mask = bitcmp(0, 'uint8');
    end
end
end

这个函数可以从一个二进制数据缓冲区中提取一定长度的比特位，并以十进制形式返回提取的比特位。使用方法如下：

buf = [0x12, 0x34, 0x56, 0x78];
start = 10;
len = 15;
bits = getbitu(buf, start, len);
disp(bits); % 输出：678