new utilities.

the .C files compile but are renamed to avoid building automatically.

src/cmd/factor.c

@@ -0,0 +1,96 @@
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+
+#define	whsiz	(sizeof(wheel)/sizeof(wheel[0]))
+
+double	wheel[] =
+{
+	 2,10, 2, 4, 2, 4, 6, 2, 6, 4,
+	 2, 4, 6, 6, 2, 6, 4, 2, 6, 4,
+	 6, 8, 4, 2, 4, 2, 4, 8, 6, 4,
+	 6, 2, 4, 6, 2, 6, 6, 4, 2, 4,
+	 6, 2, 6, 4, 2, 4, 2,10,
+};
+
+Biobuf	bin;
+
+void	factor(double);
+
+void
+main(int argc, char *argv[])
+{
+	double n;
+	int i;
+	char *l;
+
+	if(argc > 1) {
+		for(i=1; i<argc; i++) {
+			n = atof(argv[i]);
+			factor(n);
+		}
+		exits(0);
+	}
+
+	Binit(&bin, 0, OREAD);
+	for(;;) {
+		l = Brdline(&bin, '\n');
+		if(l ==  0)
+			break;
+		n = atof(l);
+		if(n <= 0)
+			break;
+		factor(n);
+	}
+	exits(0);
+}
+
+void
+factor(double n)
+{
+	double quot, d, s;
+	int i;
+
+	print("%.0f\n", n);
+	if(n == 0)
+		return;
+	s = sqrt(n) + 1;
+	while(modf(n/2, &quot) == 0) {
+		print("     2\n");
+		n = quot;
+		s = sqrt(n) + 1;
+	}
+	while(modf(n/3, &quot) == 0) {
+		print("     3\n");
+		n = quot;
+		s = sqrt(n) + 1;
+	}
+	while(modf(n/5, &quot) == 0) {
+		print("     5\n");
+		n = quot;
+		s = sqrt(n) + 1;
+	}
+	while(modf(n/7, &quot) == 0) {
+		print("     7\n");
+		n = quot;
+		s = sqrt(n) + 1;
+	}
+	d = 1;
+	for(i=1;;) {
+		d += wheel[i];
+		while(modf(n/d, &quot) == 0) {
+			print("     %.0f\n", d);
+			n = quot;
+			s = sqrt(n) + 1;
+		}
+		i++;
+		if(i >= whsiz) {
+			i = 0;
+			if(d > s)
+				break;
+		}
+	}
+	if(n > 1)
+		print("     %.0f\n",n);
+	print("\n");
+}