mpfr numbers are limited to 301,033 digits

[the-stanely]

Closed...
I learned from casevh on stackoverflow that precision is specified in bits, so for n desired digits of decimal precision, n * log(10)/log(2) bits precision are needed.

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Using:

• 64-bit, Windows 10, 1809
• Anaconda Python 64-bit 3.7.3
• gmpy2, GPy-1.9.8-cp37-cp37m-win_amd64.whl, installed from uci.edu.

Simple test to create a million digit number fails.

import gmpy2                # Get the gmpy2 library

print('max_precision =', gmpy2.get_max_precision())
print('emin_min =', gmpy2.get_emin_min())
print('emax_max =', gmpy2.get_emax_max())
gmpy2.get_context().precision = 1000000 + 3   # Set the precision context.
print(gmpy2.get_context())

million_string = 'a million character number for pi from http://www.eveandersson.com/pi/digits/1000000, must strip out newlines.'

print('string =', million_string)

million_pi = gmpy2.mpfr(million_string)
 
print('\n\nNext, print the mpfr...\n\n')
print(str(million_pi))

Printing the string representation of the million digit string works fine, showing that the input is correct. Printing the mpfr number is limited to 301,033 digits. My tests show that internal arithmetic is only performed to the same number of digits because the last digit is not being rounded correctly.

Attached is the Python script with the million digit pi as a string.

Thanks for looking at this.

gmpy2-mpfr-test.py.txt