http://benji3up2kxewkqfcq7buxk2xd6zwy3zggnurkrm3l4cvwy2iipvyyad.onion/mirrors/gmpdoc/Integer-Division.html
The f stands for
“floor”. tdiv rounds q towards zero, and r will have the same sign
as n . The t stands for “truncate”. In all cases q and r will satisfy n = q * d + r , and r will satisfy 0<=abs( r )<abs( d ) .