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unroll the pow loop in rcp

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This commit is contained in:
Ahmet Inan 2026-04-27 04:43:35 +02:00
commit 01438be6e1
2 changed files with 15 additions and 3 deletions
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6
mersenne_31.hh
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@ -114,7 +114,11 @@ Mersenne31 pow(Mersenne31 a, uint32_t m)
Mersenne31 rcp(Mersenne31 a)
{
return pow(a, a.P - 2);
Mersenne31 t = a;
a *= a;
for (int i = 0; i < 29; ++i)
t *= a *= a;
return t;
}
Mersenne31 div(Mersenne31 a, Mersenne31 b)

12
tests/m31_test.cc
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@ -12,9 +12,10 @@ Copyright 2026 Ahmet Inan <inan@aicodix.de>
#include <functional>
#include "mersenne_31.hh"
typedef CODE::Mersenne31 M31;
void random_test(uint32_t count)
{
typedef CODE::Mersenne31 M31;
std::random_device rd;
typedef std::default_random_engine generator;
typedef std::uniform_int_distribution<int> distribution;
@ -27,7 +28,7 @@ void random_test(uint32_t count)
assert((M31(a) * M31(b))() == uint32_t((uint64_t(a) * b) % M31::P));
}
}
for (uint32_t i = 0; i < count; ++i) {
for (uint32_t i = 0; i < count * count; ++i) {
uint32_t a = rand1();
assert(rcp(M31(a)) * M31(a) == M31(1));
}
@ -47,8 +48,15 @@ void random_test(uint32_t count)
}
}
void exhaustive_test()
{
for (uint32_t a = 1; a < M31::P; ++a)
assert(rcp(M31(a)) * M31(a) == M31(1));
}
int main()
{
//exhaustive_test();
random_test(10000);
std::cerr << "Mersenne 2^31-1 prime field arithmetic test passed!" << std::endl;
return 0;