diff --git a/util.c b/util.c
index 5bd7d59..d6a6be9 100644
--- a/util.c
+++ b/util.c
@@ -10,7 +10,91 @@
  * Dedication along with this software. If not, see
  * <http://creativecommons.org/publicdomain/zero/1.0/>.
  */
+/* srand48 visibility for GLIBC */
+#if !defined(__OpenBSD__)
+#define _DEFAULT_SOURCE
+#endif
+
+#include <errno.h>
+#include <stdarg.h>
+#include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+
+#include "util.h"
+
+void
+err(int eval, const char *fmt, ...)
+{
+	va_list ap;
+	int saved_errno;
+
+	saved_errno = errno;
+	va_start(ap, fmt);
+	fprintf(stderr, "%s: ", xgetprogname());
+	if (fmt != NULL) {
+		vfprintf(stderr, fmt, ap);
+		fprintf(stderr, ": ");
+	}
+	fprintf(stderr, "%s\n", strerror(saved_errno));
+	va_end(ap);
+
+	exit(eval);
+}
+
+void
+errx(int eval, const char *fmt, ...)
+{
+	va_list ap;
+	int saved_errno;
+
+	saved_errno = errno;
+	va_start(ap, fmt);
+	if (fmt != NULL) {
+		fprintf(stderr, "%s: ", xgetprogname());
+		vfprintf(stderr, fmt, ap);
+		fprintf(stderr, "\n");
+	}
+	va_end(ap);
+
+	exit(eval);
+}
+
+long double
+parse_double(const char *nptr)
+{
+	char *end;
+	long double v;
+
+	errno = 0;
+	v = strtold(nptr, &end);
+	if (nptr == end || *end != '\0' || (v == 0 && errno == EINVAL))
+		errx(1, "invalid number: %s", nptr);
+	if (errno == ERANGE)
+		errx(1, "number out of range: %s", nptr);
+
+	return v;
+}
+
+long long
+parse_integer(const char *nptr, long long minval, long long maxval)
+{
+	char *end;
+	long long v;
+
+	errno = 0;
+	v = strtoll(nptr, &end, 10);
+	if (nptr == end || *end != '\0' || (v == 0 && errno == EINVAL))
+		errx(1, "invalid number: %s", nptr);
+	if (v == 0 && errno == ERANGE)
+		errx(1, "number out of range: %s", nptr);
+	if (v < minval)
+		errx(1, "number too low: %s", nptr);
+	if (v > maxval)
+		errx(1, "number too high: %s", nptr);
+
+	return v;
+}
 
 const char *
 xgetprogname(void)
diff --git a/util.h b/util.h
index 3bb406d..3ab3df1 100644
--- a/util.h
+++ b/util.h
@@ -12,5 +12,9 @@
  */
 #define nelems(_a) (sizeof((_a)) / sizeof((_a)[0]))
 
+void err(int, const char *, ...);
+void errx(int, const char *, ...);
+long double parse_double(const char *);
+long long parse_integer(const char *, long long, long long);
 const char * xgetprogname(void);
 void xsrand48(long);