[issue40446] pow(a, b, p) where b=int((p-1)/2) spits out gibbrish for big p
New submission from Basic ICT Repairs : Hi, I was calculating Legendre coefficients, and quadratic residues and encountered what I believe to be a bug while using this code: for a in range (5): exp=int((p-1)/2) x=pow(a,exp,p) print(x) If p is an odd prime, then x can have three values [-1,0,-1] - where "-1" refers to p-1. The code works well for reasonably small primes (like 9973). But with big primes(see below), python 3.7 spits out gibberish. Same code in python 2.7 works well. The problem in python 3.7 can be avoided if exp is defined thusly : exp=(p-1)//2 Here is the prime I tried it on : p = 101524035174539890485408575671085261788758965189060164484385690801466167356667036677932998889725476582421738788500738738503134356158197247473850273565349249573867251280253564698939768700489401960767007716413932851838937641880157263936985954881657889497583485535527613578457628399173971810541670838543309159139 -- messages: 367735 nosy: Basic ICT Repairs priority: normal severity: normal status: open title: pow(a,b,p) where b=int((p-1)/2) spits out gibbrish for big p ___ Python tracker <https://bugs.python.org/issue40446> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue40446] pow(a, b, p) where b=int((p-1)/2) spits out gibbrish for big p
Basic ICT Repairs added the comment: Hi, I was calculating Legendre coefficients, and quadratic residues and encountered what I believe to be a bug while using this code: for a in range (5): exp=int((p-1)/2) x=pow(a,exp,p) print(x) If p is an odd prime, then x can have three values [-1,0,1] - where (-1) refers to (p-1). The code works well for reasonably small primes (like 9973). But with big primes(see below), python 3.7 spits out gibberish. Same code in python 2.7 works well. The problem in python 3.7 can be avoided if exp is defined thusly : exp=(p-1)//2 Here is the prime I tried it on : p = 101524035174539890485408575671085261788758965189060164484385690801466167356667036677932998889725476582421738788500738738503134356158197247473850273565349249573867251280253564698939768700489401960767007716413932851838937641880157263936985954881657889497583485535527613578457628399173971810541670838543309159139 -- type: -> behavior versions: +Python 3.7 ___ Python tracker <https://bugs.python.org/issue40446> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
