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// #include <iostream>
// #include <bitset>
#include <cstring>
#include <cassert>
#include "rng.h"
using namespace std;
//adapted from http://blog.regehr.org/archives/1063 (rotl32c version)
inline uint64_t rotl64(uint64_t x,uint32_t n){
assert(n<64);
return (x<<n)|(x>>(-n&63));
}
inline uint64_t rotr64(uint64_t x,uint32_t n){
assert(n<64);
return (x>>n)|(x<<(-n&63));
}
KeyRng::KeyRng(const char *key_,int keylen_)
:keylen(keylen_),idx(0),state(0){
assert(keylen>0);
assert(key_);
key=new uint8_t[keylen];
memcpy(key,key_,keylen);
stir();
}
KeyRng::KeyRng(const string &key_)
:keylen(key_.size()),idx(0),state(0){
assert(keylen>0);
key=new uint8_t[keylen];
memcpy(key,key_.data(),keylen);
stir();
}
KeyRng::~KeyRng(){
delete[] key;
}
void KeyRng::stir(){
for(int i=0;i<10;i++)get();
}
uint32_t KeyRng::get(){
//Progressively and cyclicly mixes in the key with the state.
//Mostly own creation; the "tempering" part is derived from a (part of a) Mersenne Twister implementation.
//In terms of distribution of values, this is similar to arc4random().
//This passes DieHarder 3.31.1 (tested 2016/10/06) with 2 "weak" results. The initial key "wachtwoord" was used.
//At least n subsequent values should be independent, where n is the length of the initial key.
state^=key[idx];
state+=17;
key[idx]+=13;
idx=(idx+1)%keylen;
state^=rotr64(state,11); //tempering
state^=rotl64(state,7)&0x9d2c5680;
state^=rotr64(state,18);
// cerr<<bitset<64>(state)<<endl;
return state>>32;
}
uint32_t KeyRng::get_uniform(uint32_t upbound){
if(upbound<=1)return 0;
uint32_t min=((uint64_t)1<<32)%upbound; //this is the amount of unusable RNG outputs when avoiding modulo bias
while(true){
uint32_t v=get();
if(v>=min)return v%upbound;
}
}
uint32_t Arc4Rng::get(){
return arc4random();
}
uint32_t Arc4Rng::get_uniform(uint32_t upbound){
return arc4random_uniform(upbound);
}
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