Truncating to a given bit length

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Buddhini Angelika
Buddhini Angelika 2015-12-30
评论： Walter Roberson 2016-1-6
I have a gui which gives a result as follows. Result=a253ff09c5a8678e1fd1962b2c329245e139e45f9cc6ced4e5d7ad42c4108fc0. Is there a way to truncate the above result to a given bit length? (Say bit lengths of 19,13,10 etc.)
Please help me with the above question.
Thanks a lot in advance.

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Walter Roberson
Walter Roberson 2015-12-30
Assuming Result is a string and assuming that the values represent hex,
NeededBitLength = 19; %for example
bitvec = reshape(dec2bin(sscanf(Result,'%1x'),4).',1,[]);
bitvec = bitvec(end-NeededBitLength+1 : end);
truncatedResult = bin2dec(bitvec);
Caution: if you need more than 53 bits this version will not work.
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Buddhini Angelika
Buddhini Angelika 2016-1-6
What are symbolic numbers? And how to do it if I go for symbolic numbers?
My program generate results like above and also various integers (n). Then I need to truncate the result as above to obtain a single integer value.
Actually the Result obtained above is a result when I apply the SHA-256 to a given message word.
Please help me to solve this problem. If there is a better hash function to be used please mention it too.
Thanks a lot in advance
Walter Roberson
Walter Roberson 2016-1-6
http://www.mathworks.com/products/symbolic/
I am certain that SHA-256 does not expect you to work with word lengths of more than 64 bits. Typical implementations work with arrays of 32 bit words.

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