Random double between [0.5,1)

rand.cpp

#include <cstdio>
#include <cstdint>

// generates random number between [0.5, 1)
double getrand(FILE *f) {
	union {
		uint64_t u;
		double d;
	};
	fread(&u, sizeof(u), 1, f);
	u &= ~0xfff0'0000'0000'0000;  // mask sign and exp
	u |= 0x3fe0'0000'0000'0000;  // reset sign and exp
	return d;
}

int main() {
	FILE *f = fopen("/dev/urandom", "rb");
	for (uint64_t i = 0; i < 500'000'000; ++i) {
		double d = getrand(f);
		// printf("%f\n", d);
	}
	fclose(f);
}