Perl:寻找和读取位,而不是字节 [英] Perl: seek to and read bits, not bytes
问题描述
有没有简单的方法来做到这一点?
我意识到我可以编写一个包含常规查找和读取的子程序,但是想知道是否有更简单的解决方案。如果n是m的倍数,m是1,2,4,8,16,32中的一个,在一些平台上,你可以将整个文件读入一个字符串,并使用 vec 对于这一点。
(不可否认,这是一个相当有限的情况,但常见的情况。)
除此之外,只需要做数学;在伪代码中:
discard = n%8;
startbyte =(n-discard)/ 8
bits = m + discard
bytes = int((bits + 7)/ 8)
寻找开始字节
读取字节到字符串
@list = split //,解包$ {bits} b,字符串
拼接(@list,0,$ discard)
拼接(@list,$ m, @list)
In Perl, I want to seek to the nth bit (not byte) of a file and then read the next m bits, returned as a list of 0s and 1s.
Is there any easy way to do this?
I realize I can write a subroutine wrapping regular seek and read, but was wondering if there's a easier solution.
If n is a multiple of m, and m is one of 1, 2, 4, 8, 16, 32, and on some platforms, 64, you can read the whole file into a string and use vec for this.
(Admittedly a fairly constraining case, but a common one.)
Barring that, you'll just have to do the math; in pseudo-code:
discard = n % 8;
startbyte = (n - discard) / 8
bits = m + discard
bytes = int( (bits + 7) / 8 )
seek to startbyte
read bytes into string
@list = split //, unpack "${bits}b", string
splice( @list, 0, $discard )
splice( @list, $m, @list )
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