How to convert ZZ to binary?

Question

I'm using the NTL library to implement my code and I have to ZZ number which I have to convert to binary then take a substring from it and convert that substring into decimal. How can I do that?

ZZ N;
unsigned char pp[200];
BytesFromZZ(pp,N,NumBits(N));

The above code is giving me this error: "Segmentation fault (core dumped)"

EDIT : Above code is working now but instead of giving octal string it is returning garbage values.

BytesfromZZ but it is not working. I am looking for something inbuild. — Pratibha, Feb 04 '13 at 09:34
I dont understand why people are downvoting instead of giving solution. — Pratibha, Feb 04 '13 at 09:52
Because you've shown no code. Show us what you have and where it is failing and we may be able to help. — Joe, Feb 04 '13 at 10:05
I have edited the question and added the code lines. Sorry but it is not formatting as code even after using 4 blanks. — Pratibha, Feb 04 '13 at 10:07
At a glance, you typically want to allocate a buffer before trying to fill it. — Hasturkun, Feb 04 '13 at 10:30
AFAICT from [this page](http://www.shoup.net/ntl/doc/ZZ.txt), `BytesFromZZ` returns raw bytes, not an octal string. I also note that you're using `NumBits()` instead of `NumBytes()`, which is probably wrong. — Hasturkun, Feb 04 '13 at 12:21

Philipp Grigoryev · Answer 1 · 2014-02-26T07:46:56.720

1

You should use NumBytes, and a result is a reversed string.

edited Feb 26 '14 at 07:46

answered Feb 26 '14 at 07:36

Philipp Grigoryev

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score 1 · Answer 2 · answered Sep 28 '20 at 14:52

The array pp which holds the byte-representation of N must be allocated with size equal to NumBytes(N). Otherwise, you get a SegFault if the length of pp is less than NumBytes(N). In addition, probably because of the Little-Endianess of Intel CPUs, pp represents N as a byte-string in reversed order.

ZZ N;
// assigning whatever value to N
unsigned char* pp = new unsigned char[NumBytes(N)];
BytesFromZZ(pp, N, NumBytes(N)); // pp = byte-representation of N
delete[] pp;

How to convert ZZ to binary?

2 Answers2