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Calculate modular inverse
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| # Note: A and P must share no factor greater than 1. | |
| def modular_inverse(A,P): | |
| p0, a0 = 1, 0 | |
| p1, a1 = 0, 1 | |
| R0, R1 = P, A%P | |
| while R1 != 1 and R1 != 0: | |
| n, R2 = divmod(R0, R1) | |
| p2 = p0 - n*p1 ; a2 = a0 - n*a1 | |
| p0 = p1; a0 = a1; p1 = p2; a1 = a2 | |
| R0 = R1; R1 = R2 | |
| if R1 == 0: | |
| # return "Error: A and P share factor "+ str(R0) + ". They must share no factor greater than 1." | |
| return a1 % P |
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