qsort example

qsortExample.cpp

#include <iostream>
#include <vector>
#include <cstdlib>
#include <cstdint>
#include <cstring>

/**
 * g++ -O3 qsortExample.cpp
 *
 * # MinGW
 * g++ -O3 qsortExample.cpp -lbcrypt
 */

#ifdef _WIN32
#define WIN32_NO_STATUS
#include <windows.h>
#undef WIN32_NO_STATUS

#include <winternl.h>
#include <ntstatus.h>
#include <winerror.h>
#include <bcrypt.h>
#include <sal.h>

void randombytes(unsigned char *x, unsigned long long xlen) {
	if (!NT_SUCCESS(BCryptGenRandom(nullptr,x,xlen,BCRYPT_USE_SYSTEM_PREFERRED_RNG))) {
		_Exit(-1);
	}
}

#else

#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

ssize_t readAll(int fd, void* buf_, size_t count) {
    auto buf = (uint8_t*)buf_;
    size_t alreadyRead = 0;
    size_t remaining = count;
    for(;;) {
        ssize_t curr = read(fd, buf+alreadyRead,remaining);
        if (curr <= 0) return curr; // EOF

        remaining -= curr;
        alreadyRead += curr;

        if (remaining == 0) return count; // all expected bytes read
    }
}

void readAllOrExit(int fd, void* buf, size_t count) {
    ssize_t readBytes = readAll(fd,buf,count);
    ssize_t count_ = count;
    if (readBytes < count_) _Exit(-2);
}

void randombytes(unsigned char *x, unsigned long long xlen) {
    static int fd = -1;
    if(fd < 0) {
        if((fd = open("/dev/urandom",O_RDONLY))==-1) _Exit(-1);
    }
    readAllOrExit(fd,x,xlen);
}

#endif

constexpr size_t VSZ = 128*1048576;
constexpr size_t ISZ = 64;
constexpr size_t nmemb = VSZ/ISZ;

int comp(const void* p1, const void* p2) {
    return memcmp(p1,p2,ISZ);
}

int main() {
    std::vector<uint8_t> v(VSZ,0);
    randombytes(&v[0],VSZ);
    std::cout<<"RNG OK"<<std::endl;
    std::cout<<"Items:"<<nmemb<<std::endl;
    qsort(&v[0],nmemb,ISZ,comp);
    std::cout<<"SORT OK"<<std::endl;
}