I am trying to do twos compliment of the following: 34-11.
After trying to solve the problem myself and then getting the answer from a calculator I am doing it completely wrong after following many tutorials.
I converted 34 and 11 to binary first getting 100010 and 1011 respectively. I then got 0101 by 1s notation and adding 1 after.
Finally, 100010 + 0101 = 100111.
From what I can find this is not the correct answer. I would appreciate if someone could walk me through it, thanks.
Related
If n = 100011 in binary, then I want to retrieve the positions of set bits which in this case are 1,5,6 when measured from left to right.
How to calculate such positions without literally checking for bit is zero or not by going to every bit position?
In the most common convention, a binary number is written in the order as a number in other common positional representations (decimal etc): with the least significant digit in the rightmost position. It also makes more sense to label that digit as "digit zero", so that the label of every digit corresponds with the exponent in the associated weight (eg bit 0 has weight 20=1 and so forth). This doesn't really matter, it's easy enough to re-number the digits, but it's usually easier to follow the conventions.
Since you asked
How to calculate such positions without literally checking for bit is zero or not by going to every bit position?
I will address that portion of the question. Checking the bits one by one is not completely disastrous however. Even for BigInts. The number of results could be as high as the number of bits anyway. For numbers known to be sparse, there is still not much that can be done - every bit has to be checked somehow because if any bit is ignored completely, that bit might have been set and we'd miss it. But in the context of a machine word, there are tricks, for example based on find-first-set.
Using the find-first-set function (or count trailing zeroes), the index of the set bit with the lowest index can be found in one step (if you accept this function as being one step, which is a reasonable assumption on most hardware, and in theory you can just define it to be one step), and then that bit can be removed so the next find-first-set will find the index of the next bit. For example:
while bitmask != 0:
yield return find-first-set(bitmask)
bitmask &= bitmask - 1 // remove lowest set bit
This is easy to adapt to BigInts, just do this on every limb of the number and add the appropriate offset.
To do that you use masks.
Each position from right to left is a power of two.
For example 0101 is 1*2ˆ0 + 0*2ˆ1 + 1*2ˆ2 + 0*1ˆ3 = 1+0+4+0 = 5
Then to check if these two bits are on against a bytesToTest variable you AND with 5: byteToTest & 5 == 5
Given that 1 & 0 = 0 and 1 & 1 = 1
If bytesToTest is 1111 then 1111 & 0101 will give 0101
If bytesToTest is 1010 then 1010 & 0101 will give 0000
Following this reasoning for the particular case of 100011
To retrieve 1, 5, and 6 from left to right (the three ones set to 1)
The mask is: 1+2+32 = 35
With this information you should be able to define individual masks for each bit, test one by one, and be able to answer in which position you find bits that are on and in which bits that are off.
Given decimal number=12
One way to find 9s complement is to simply find 10s complement and subtract 1. By this method I get answer=87.
However can i solve this problem by first finding the equivalent of 12 in base 9 number system which would be 13. Now if I find 9s complement of this number using the formula r^n -N answer would be 81-12.
Please suggest what's wrong ?
I really need help understanding twos complement. I have been set with the task of converting some negative numbers into binary using 8 bit Two's complete but I have literally no idea what I have to do. Can someone help, if someone could explain it in the simplest way that would be really helpful. Thanks again
The simplest way is :
from right to left start copying all digits untill you get a 1, copy it too, then invert all the rest,
so 1111 1011, you start copying the 1, you reached the first one, so next start inverting the rest:
0000 0101 witch is -5.
another example: 1111 1000 -> 0000 1000 that is -8
I hope it helps.
more info: Two's complement
The simplest way is to add 256 to the number.
For example, if you have -42, the two's complement is:
256 + -42 = 214
214 in binary is 11010110.
You can also do the calculation in binary, then you would subtract 42 from 256:
100000000
- 101010
----------
11010110
I'm having some troubles with the SEC/DED error correction code. It seems I've found some cases in which the decoder thinks a double bit flip occured but only one really occured. I suppose I did somthing wrong, but I was not able to understand what.
Let me show you an example.
Suppose I want to encode the 4 bits 1011 using a (7,4) code plus an extra bit needed to perform the two-error-detection. The coded word should be 00110011, where the most significant bit is the extra parity bit, the following two are p0 and p1 and so on.
Now, let's suppose that during a transmission the less significant bit is flipped; thus the received word will be 00110010. The receiver will extract from this code the four received data bits 1010 and will construct a new code which will result 01011010. Finally the receiver will perform a bitwise xor of the two codes obtaining 0111. The last three bits says that bit 7 has been flipped (which is right), but the first bit is 0 and, as far as i know, the decoder should consider this situation as if more than a bit flip has occured.
What did I do wrong?
I think I've solved the problem.
In the example above I calculate the syndrome and then I compute a new overall parity bit of the resultant codeword. Instead, I should check the overall parity of the received word and set the error_happened boolean to that value; then calculate the syndrome.
Outside the binary 01010, octal 01122, decimal integer 1234 and hexadecimal 0xFF, does any one have any idea or trick how to build a new number format? For example, 0x11AEGH has it's range from 0 - 9 to A - H. I'm going to build password generator, so it would be very helpful if anyone can put something on it that might help.
Firstly, Is there any function which can do this? Basically I want to convert 0x11AEGH to binary, octal, integer and so on...
Formatting a number in an N-ary system requires two things: an alphabet, and an ability to obtain results of integer division + the remainder.
Consider formatting a number in a base-26 system using the Latin alphabet. Repeatedly obtain the remainder R of division by 26, pick letter number R, and add it to the front of the number that you are formatting. Integer-divide the number by 26, and use it in the next step of the algorithm. Stop when you reach zero.
For example, if you print 1234 in base-26, you can do it like this:
1234 % 26 is 12. Add M; 1234/26 is 47
47 % 26 is 21. Add V; 47 / 26 is 1
1 % 26 is 1. Add B. 1 / 26 is zero; stop.
So 1234 in base-26 is BVM.
To convert back, start from the front, and sequentially subtract the designated "zero" (A in case of the above example) from each digit, like this:
B-A is 1. Result is 1
V-A is 21. Result is 1*26+21, which is 47
M-A is 12. Result is 47*26+12, which is 1234.
You can probably use functions like Long.parseLong(String representation, int radix) and Long.toString(long value, int radix) as they are in Java. Other languages may also have the similar features.
This approach restricts the maximal possible radix (base) and you have no control over the characters representing different digits (alphanumeric chars are used). However it is a ready solution without any extra coding.