Question

Is it possible to get more than 100 decimal digits in C#?

If yes what is the necessary portion of code?

In Java there something call BigDecimal but it still can’t reach more than 55 digits.

Answer 1

Using J# libraries:

Download the J# Redistributable to obtain the J# class libraries. This article hints about how to use it to get ZIP-ability in your .NET projects, and explains a bit about BigDecimal, but as Ramhound explained, the article is relatively old.

After download, add the vsjlib to your project. It didn’t work for me on .NET 4.0, but it did work on 2.0 project. It contains a BigDecimal class, among others. Not sure, however, if that gives you up to 100 decimals, but you might give it a try.

Using MPIR — Multi Precision Integers and Rationals

You can download a wrapper for the MPIR library for .NET here (download version 0.2). Then, do the following:

• Add the the files \wrapper.*.dll to your project, make sure that on each built they are copied to your Debug or Release directory.
• Add \wrapper\xmpir.cs to your project

• Add the following code to your project:

  // set the precision to 512 bits (adjust this to your needs)
  mpir.mpf_set_default_prec(512);
  ulong default_prc = mpir.mpf_get_default_prec();
  
  // init vars (important!)
  mpir.mpf_t val = mpir.mpf_init_set_d(.5);
  mpir.mpf_t result = mpir.mpf_init_set_ui(0);
  
  // calculate 0.5^200
  mpir.mpf_pow_ui(result, val, 200);
  double dresult = mpir.mpf_get_d(result);
  
  // convert result to a string, in the form 1.2345 (dot not in output) and exp holding exponent
  long exp;
  string sresult = mpir.mpf_get_string(out exp, 10, 0, result);
  
  // free vars (important!)
  mpir.mpf_clear(val);
  mpir.mpf_clear(result);
  

Note that the variable sresult will only hold the significant digits. You’ll have to add the logic for printing the exponent as well, or a bunch of zeroes.

Result is 6.2230152778611417071440640537801242405902521687211671331011166147896988340353834411839448231257136169569665895551224821247160434722900390625E-60

A documentation PDF file on the full MPIR library shows how to use it in more detail.