how to compress a string of numbers

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2.00/5 (2 votes)

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hello everyone
I've been trying to come up with a way to condense (compress) a large string that only contains number
is it possible to combining each couple of numbers and represent them in 8 bits instead of having each character take up the entire octet

Here is my input sample:

"543216548798654321320000654897986321"

each two numbers should take up 8 bits

thank you

Posted 4-Jan-16 9:50am

Member 12223678

Updated 25-Apr-20 5:38am

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Comments

Sergey Alexandrovich Kryukov 4-Jan-16 16:10pm

Of course, this is fairly simple. What have you tried so far?
What you suggested is the simplest, but not the best compression: 8 bits can store 256 numbers, but you want to store 100 (0-99).
—SA

Matt T Heffron 4-Jan-16 17:05pm

"... 16 8 bits can store 256 numbers..."
FTFY ;-)

Sergey Alexandrovich Kryukov 4-Jan-16 17:21pm

8, 8... :-)
—SA

Patrice T 4-Jan-16 18:15pm

What have you done so far ?
Even number of figures is rather easy to handle. but odd number of figures is more tricky.

PIEBALDconsult 4-Jan-16 19:12pm

Yes.

2 solutions

Solution 1

if you are REALLY SURE, that it will only be decimal numbers you can go as easy as this:

C++

char digit1 = sample[i];
int value1 = digit1 - '0'; //is between 0 and 9

char digit0 = sample[i+1];
int value0 = digit0 - '0'; //is between 0 and 9
int number = value1 * 10 + value0;

byteBuffer[n] = (byte) number;

The value number is ensured to be below 128 (7 bits), so you can spare out 1 bit and save the value in 7 bits. But that is advanced stuff and you should understand it like here from Microsoft fine explained.

Posted 4-Jan-16 23:25pm

KarstenK

Comments

CPallini 5-Jan-16 5:51am

5.

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Member 12223678 · Accepted Answer · 2016-01-05T10:15:00

Solution 2

C++

unsigned int i;
	const char *s = "123465789";
	vector<char> num;
	for (i=0;i<strlen(s);i+=2)
	{
		num.push_back((s[i]-'0') + (s[i+1]-'0')*10);
	}

would something like this work ?
will the size of the vector num be half the size of the string s ??

Posted 5-Jan-16 10:15am

Member 12223678

Updated 5-Jan-16 10:20am

v4

Comments

Matt T Heffron 5-Jan-16 17:05pm

As written it will omit the last digit of an odd length string. Also, be careful how this sequence of "char"s is used. If handed to any functions expecting a string, the occurrence of a 0 value could cause it to appear truncated. Perhaps you should "OR" in 0x80 to the value so it cannot be 0.