separate humansize into a util function

also show 1 decimal of human size string like: 4M -> 4.4M

util/human.c

@@ -0,0 +1,21 @@
+#include <stdio.h>
+#include <string.h>
+
+#include "../util.h"
+
+char *
+humansize(double n)
+{
+	static char buf[16];
+	const char postfixes[] = " KMGTPE";
+	size_t i;
+
+	for(i = 0; n >= 1024 && i < strlen(postfixes); i++)
+		n /= 1024;
+
+	if(!i)
+		snprintf(buf, sizeof(buf), "%lu%c", (unsigned long)n, postfixes[i]);
+	else
+		snprintf(buf, sizeof(buf), "%.1f%c", n, postfixes[i]);
+	return buf;
+}