path: root/rnd.c

/* See LICENSE file for copyright and license details. */
#include "common.h"


static char reservoir[128U << 10];
static size_t reservoir_off = sizeof(reservoir);
static int random_fd;
static const char *random_fname;


size_t
max_blksize(void)
{
	size_t ret = sizeof(reservoir);
	while (ret & (ret - 1U))
		ret &= ret - 1U;
	return ret;
}


void
init_random(int fd, const char *fname)
{
	struct stat st;

	random_fname = fname;
	random_fd = fd;

	errno = 0;
	if (isatty(random_fd) || errno == EBADF) {
	use_builtin_generator:
		random_fd = -1;
		libsimple_srand();
	} else if (fstat(random_fd, &st)) {
		if (errno == EBADF)
			goto use_builtin_generator;
		eprintf("fstat %s:", random_fname);
	} else if (S_ISFIFO(st.st_mode) || S_ISCHR(st.st_mode) || S_ISSOCK(st.st_mode)) {
		eprintf("%s is of a unsupported inode type (must be TTY, character device, FIFO, or socket)", fname);
	}
}


const char *
get_random(size_t needed)
{
	size_t off;
	ssize_t r;

	if (sizeof(reservoir) - reservoir_off >= needed)
		return &reservoir[reservoir_off];

	if (random_fd < 0) {
		libsimple_random_bytes(&libsimple_random_bits, NULL, reservoir, reservoir_off);
		reservoir_off = 0;
		return reservoir;
	}

	for (off = 0; off < reservoir_off;) {
		r = read(random_fd, &reservoir[off], reservoir_off - off);
		if (r <= 0) {
			if (!r)
				eprintf("random source depleted");
			if (errno == EINTR)
				continue;
			eprintf("read %s:", random_fname);
		}
		off += (size_t)r;
	}

	reservoir_off = 0;
	return reservoir;
}


void
used_random(ssize_t amount)
{
	reservoir_off += (size_t)amount;
}