How to generate a large integer from smaller integers?

e.g {67,114,121} should yield a biginteger 4420217. also vice versa...4420217 should be converted back to {67,114,121}..some function similar to Mathematica function FromDigits[list,b]-takes the digits to be given in base b and constructs an integer from the list of its digits.

Answer 1

[Stephen23]

Pure math solution, no bit-bashing:

>> val = 4420217;
>> vec = fix(mod(val./256.^(floor(log2(val)/8):-1:0),256))
vec =
    67   114   121
>> sum(vec.*256.^(numel(vec)-1:-1:0))
ans =
     4420217

[jalashree trivedi]

thanx!!

Answer 2

[Walter Roberson]

X = [67,114,121];
sum(X.*256.*(length(X)-1:-1:0))

[jalashree trivedi]

thanx..but how can i reverse it back again? im workin on ecc algo where i need to encrypt as well as decrypt the same..

[Walter Roberson]

typecast(swap(uint32(Number) ), 'uint8')

[Walter Roberson]

You can also use typecast to create the numbers but you have to pad with 0 before doing the typecast. You also need to swap the bytes after doing the typecast.