我在十六进制转储中有数据,但是不知道编码.例如. 0x91 0x05 = 657 [英] I have data in hex dump but don't know the encoding. Eg. 0x91 0x05 = 657
问题描述
我在hexdump代码中有一些数据. 左手是DEC,右手是十六进制转储代码.
I have some data in hexdump code. left hand are DEC and right hand are hexdump code.
16 = 10
51 = 33
164 = A4 01
388 = 84 03
570 = BA 04
657 = 91 05
1025 = 81 08
246172 = 9C 83 0F
如何计算DEC的十六进制转储? 在perl中,我尝试使用ord()命令,但不起作用.
How to calculate any hexdump to DEC ? In perl, I tried to use ord() command but don't work.
更新 我不知道这叫什么.看起来像7位数据.我尝试在excel中建立公式,如下所示:
Update I don't known what it call. It look like 7bits data. I try to build formula in excel look like these:
DEC = hex2dec(X) + (128^1 * hex2dec(Y-1)) + (128^2 * hex2dec(Z-1)) + ...
推荐答案
您所拥有的是可变长度编码.长度使用哨兵值的形式进行编码:编码数字的每个字节(最后一个字节除外)的高位均已设置.其余的位以低端字节顺序形成数字的二进制补码.
What you have is a variable-length encoding. The length is encoded using a form of sentinel value: Each byte of the encoded number except the last has its high bit set. The remaining bits form the two's-complement encoding of the number in little-ending byte order.
0xxxxxxx ⇒ 0xxxxxxx
1xxxxxxx 0yyyyyyy ⇒ 00yyyyyy yxxxxxxx
1xxxxxxx 1yyyyyyy 0zzzzzzz ⇒ 000zzzzz zzyyyyyy yxxxxxxx
etc
以下内容可用于解码流:
The following can be used to decode a stream:
use strict;
use warnings;
use feature qw( say );
sub extract_first_num {
$_[0] =~ s/^([\x80-\xFF]*[\x00-\x7F])//
or return;
my $encoded_num = $1;
my $num = 0;
for (reverse unpack 'C*', $encoded_num) {
$num = ( $num << 7 ) | ( $_ & 0x7F );
}
return $num;
}
my $stream_buf = "\x10\x33\xA4\x01\x84\x03\xBA\x04\x91\x05\x81\x08\x9C\x83\x0F";
while ( my ($num) = extract_first_num($stream_buf) ) {
say $num;
}
die("Bad data") if length($stream_buf);
输出:
16
51
164
388
570
657
1025
246172
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