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64 bit number modulo mersenne number (M61, 2^61-1) compiles with no multiplication or division with gcc 9.4 -O3
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| #include <stdint.h> | |
| #define MP(p) ((1uLL << p) - 1) | |
| uint64_t mod_m61(uint64_t a) | |
| { | |
| uint64_t tmp = (a & MP(61)) + (a >> 61); | |
| if (tmp >= MP(61)) | |
| tmp -= MP(61); | |
| return tmp; | |
| } | |
| // a simple (a % MP(61)) compiles with a multiplication and longer instruction sequence |
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