sigonasr2/FastModularExponentiation
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Co-authored-by: sigonasr2 <sigonasr2@gmail.com>
This commit is contained in:
Nic0Nic0Nii 2023-06-13 18:51:10 +00:00
parent fce397b68b
commit 7d8bb3561a
4 changed files with 29 additions and 11 deletions
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4
main.cpp
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@ -61,8 +61,8 @@ struct Data{
int main() int main()
{ {
utils::PowMod(5,117,19); std::cout<<utils::PowMod(5,117,19)<<std::endl;
utils::PowMod(5,117,19); std::cout<<utils::PowMod(98765,1234,123557)<<std::endl;
std::cout<<"Works!"<<std::endl; std::cout<<"Works!"<<std::endl;
return 0; return 0;
} }

30
utils.cpp
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@ -3,16 +3,34 @@
std::map<internal::PowModStruct,int>utils::mapping; std::map<internal::PowModStruct,int>utils::mapping;
int utils::PowMod(int a,int b, int mod){ long utils::PowMod(int a,int b, int mod){
int shift=0; int shift=0;
for(int n=1;n<=b;n*=2){ long product=0;
for(long n=1;n<=b;n*=2){
if(utils::mapping.find({a,n,mod})!=utils::mapping.end()){ if(utils::mapping.find({a,n,mod})!=utils::mapping.end()){
std::cout<<internal::PowModStruct{a,n,mod}<<"="<<utils::mapping[{a,n,mod}]<<std::endl; if(b&n){
if(product==0){
product=1;
}
std::cout<<utils::mapping[{a,n,mod}]<<std::endl;
product*=utils::mapping[{a,n,mod}];
product%=mod;
}
continue; continue;
} }
std::cout<<std::fmod(std::pow(double(a),double(n)),double(mod))<<std::endl; if(n==1){
utils::mapping[{a,n,mod}]=std::fmod(std::pow(double(a),double(n)),double(mod)); utils::mapping[{a,n,mod}]=a%mod;
}else{
utils::mapping[{a,n,mod}]=long(utils::mapping[{a,n/2,mod}])*utils::mapping[{a,n/2,mod}]%mod;
}
if(b&n){
if(product==0){
product=1;
}
product*=utils::mapping[{a,n,mod}];
product%=mod;
}
shift++; shift++;
} }
return 0; return product%mod;
} }

6
utils.h
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@ -4,9 +4,9 @@
namespace internal{ namespace internal{
struct PowModStruct{ struct PowModStruct{
int a,b,mod; long a,b,mod;
friend std::ostream& operator << (std::ostream& os, const internal::PowModStruct& rhs) { os << rhs.a << "^" << rhs.b << "%" << rhs.mod; return os; }; friend std::ostream& operator << (std::ostream& os, const internal::PowModStruct& rhs) { os << rhs.a << "^" << rhs.b << "%" << rhs.mod; return os; };
bool operator<(const internal::PowModStruct&rhs)const{return a<rhs.a||b<rhs.b||mod<rhs.mod;}; bool operator<(const internal::PowModStruct&rhs)const{return a<rhs.a||a==rhs.a&&b<rhs.b||a==rhs.a&&b==rhs.b&&mod<rhs.mod;};
}; };
} }
@ -16,5 +16,5 @@ class utils{
static std::map<internal::PowModStruct,int>mapping; static std::map<internal::PowModStruct,int>mapping;
public: public:
//a^b % mod //a^b % mod
static int PowMod(int a,int b,int mod); static long PowMod(int a,int b,int mod);
}; };