RIP #03 06 декабря 1997

Программирование

School Hacker - Cycle BASE -1 ": Hand Dragon.

                             BASE-1

                  The first seminar. Base.

                         (Continued)



    All rights training materials Hekerskoy Schools
belong Arvi Hacker (Ilya Vasilyev), Moscow,
2:5020 / 287 @ fidonet, arvi@hsys.msk.ru, 
ath@verte.dnntm.rssi.ru. If you use any part of this material 
for any purpose obligatory link to the source. In the case of 
commercial use or for teaching more than one

Rights required a preliminary agreement with the author.
This material was originally intended for students and
students, pupils Hekerskoy School.



                       B1: 5 Manual Dragon.

                       ===================


    If you feel it deeply our analogy with the dragon, then
after studying the simplified algorithms manual dragon you
give the impression that the Dragon is now very easy and fast
You listened as if he was really home, "manual". But
Attention! Once you just go outside their homes (systems
reckoning with the bases 2, 8, 16), as you will have to re-
tame and able to withstand his attack.


    Algorithms manual dragon is based on two tables Dragon
large and small. Here they are:


   +------+---+----+ +-----+---+

   | 0000 | 0 | 0 | | 000 | 0 |

   | 0001 | 1 | 1 | | 001 | 1 |

   | 0010 | 2 | 2 | | 010 | 2 |

   | 0011 | 3 | 3 | | 011 | 3 |

   | 0100 | 4 | 4 | | 100 | 4 |

   | 0101 | 5 | 5 | | 101 | 5 |

   | 0110 | 6 | 6 | | 110 | 6 |

   | 0111 | 7 | 7 | | 111 | 7 |

   | 1000 | 8 | 8 | +-----+---+

   | 1001 | 9 | 9 | Small table Dragon

   | 1010 | A | 10 |

   | 1011 | B | 11 |

   | 1100 | C | 12 |

   | 1101 | D | 13 |

   | 1110 | E | 14 |

   | 1111 | F | 15 |

   +------+---+----+
Large table Dragon


    When we draw them on paper, we usually otcherkivaem in
A large table that part of the Dragon, which coincides with the 
Small and we get two tables in one. Large table Dragon more

useful when working with hexadecimal machine type IBM PC,
and small - while working with octal machines, for example, a 
series of BC.



    These tables are so often pop up in hekerskoy life of such
seemingly with no way related sites that you still
have to learn them by heart. I izmaral small underscores,
perhaps a few general books, all the while restoring their
from memory, while not remember. I advise you not to repeat my
feat, but to learn them right now, oh how they will be useful.
:-)


    The most important application tables Dragon - transfers 
between hexadecimal and binary (large table

Dragon), and between octal and binary (Small table
Dragon).


    As we know, there are related languages. For example,
ancient Slavic, Russian, Ukrainian and Russian. If you normally
when translating from one language to another has to look in 
the dictionary unit word, when translated, say, from Ukrainian 
to Russian, sufficient to specify a table of correspondence 
between letters. For example, change the letter 'i' in 'and' a 
'and', in turn, on the 's'. 


    The role of such "kinship" of languages ​​in the number 
systems are binary and hexadecimal, binary and octal. A

translation table and the table are the Dragon. Thus, we 
explain all cases. Watch for us, there are pitfalls!



                             16 -> 2


    Well it's simple. Each hexadecimal digit placed in the
corresponds to four binary digits (bits, bit = BInary digiT) on
Large table of Dragon. After the transfer of all numbers, zeros
the left (leading zeros), if they exist, of course, can be
appropriate.


   12FC_16 = 0001 0010 1111 1100 _2 = 1001011111100_2


                             2 -> 16


    A little more complicated. The chain of binary bits is 
divided into Four _SPRAVA_ if the latter will not have enough 
toe, they are appended to the left.



   1011001011_2 = 0010 1100 1011_2 = 2CB_16


                             8 <-> 2


    Transfers between binary and octal systems are very
similar, only using small table and a breakdown of the Dragon
binary number to three bits.


   = 276_8 010 111 110_2 = 10111110_2

   1011001011_2 = 001011001 011_2 = 1313_8


    WARNING! Simplified algorithms exist only for the Dragon
Translation 16 <-> 2 8 <-> 2. For transfer of 16 <-> 8 should 
be used intermediate binary system. Using the same

Simplified algorithms for the translation of the Dragon in the 
decimal system or out-blunder. For it, you'll expelled from

Appraisal knee in the ass!


   In general, remember the formula Simplified Dragon: 8 <-> 2 
<-> 16. 


   WARNING! A common misconception!


    Every hacker in life is the period when he suddenly (as
some inexplicable reason) starts to assume that the numbers in
that do not use the letters do not change when translated into
decimal system. That is, for example, = 123_16 123_10. So,
IT IS NOT SO! Think about why. Do the math, what is the 123_16 
on The Taming of the algorithm.


>>>


    Often required to translate the bytes and words from the 
binary system in decimal. Instead of long and tedious to take on

The Taming of the algorithm, we can quickly convert a number in
hexadecimal notation, and only then out of it-in
decimal. Saves a lot of time.


   1010 1001_2 = A9_16 = 10 * 16 +9 = 169_10


   Bytes transferred immediately and in the mind!

<<<


                                        (To be continued ...)