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Python: Fast power of b modulo x
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| def fastmodpow(a, b, x): | |
| poww = res = 1 | |
| while b: | |
| if b & 1: | |
| pw, i = a, 1 | |
| while i < poww: | |
| pw *= pw | |
| pw %= x | |
| i *= 2 | |
| res *= pw | |
| res %= x | |
| poww *= 2 | |
| b /= 2 | |
| return res % x |
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