Initial commit

1 files changed, 68 insertions, 0 deletions

diff --git a/two/bit.c b/two/bit.c
new file mode 100644
index 0000000..28f0e7d
--- /dev/null
+++ b/two/bit.c
@@ -0,0 +1,68 @@
+#include <stdio.h>
+
+void
+itob(int n)
+{
+	for (int i = 15; i >= 0; --i) {
+		int j = n >> i;
+		if (j & 1) {
+			printf("1");
+		} else {
+			printf("0");
+		}
+	}
+	printf("\n");
+}
+
+/*
+ * return x with the n bits that begin at position p inverted, leaving the other
+ * bits unchanged
+ */
+void
+invert(unsigned x, int p, int n)
+{
+	int i;
+	i = 0;
+	while (n > 0) {
+		i |= 1 << p;
+		--p;
+		--n;
+	}
+	x ^= i;
+}
+
+/*
+ * return x with the n bits that begin at position p set to the rightmost n bits
+ * of y, leaving the other bits unchanged
+ */
+void
+setbits(unsigned x, int p, int n, unsigned y)
+{
+	x = x >> (p + 1 - n) & ~(~0 << n);
+	y = y & (~0 << n) | x;
+	printf("%d %d\n", x, y);
+	itob(x);
+	itob(y);
+}
+
+/* count the number of 1-bits */
+int
+bitcount(unsigned x)
+{
+	int b = 0;
+	while (x != 0) {
+		/* deletes rightmost 1-bit in x */
+		x &= (x - 1);
+		++b;
+	}
+	return b;
+}
+
+int
+main()
+{
+	/* setbits(5, 2, 3, 16); */
+	/* invert(16, 2, 1); */
+	printf("%d\n", bitcount(4));
+	return 0;
+}