Initial data commit

Task/Generator-Exponential/C/generator-exponential-1.c

@@ -0,0 +1,162 @@
+#include <inttypes.h>	/* int64_t, PRId64 */
+#include <stdlib.h>	/* exit() */
+#include <stdio.h>	/* printf() */
+
+#include <libco.h>	/* co_{active,create,delete,switch}() */
+
+
+
+/* A generator that yields values of type int64_t. */
+struct gen64 {
+	cothread_t giver;	/* this cothread calls yield64() */
+	cothread_t taker;	/* this cothread calls next64() */
+	int64_t given;
+	void (*free)(struct gen64 *);
+	void *garbage;
+};
+
+/* Yields a value. */
+inline void
+yield64(struct gen64 *gen, int64_t value)
+{
+	gen->given = value;
+	co_switch(gen->taker);
+}
+
+/* Returns the next value that the generator yields. */
+inline int64_t
+next64(struct gen64 *gen)
+{
+	gen->taker = co_active();
+	co_switch(gen->giver);
+	return gen->given;
+}
+
+static void
+gen64_free(struct gen64 *gen)
+{
+	co_delete(gen->giver);
+}
+
+struct gen64 *entry64;
+
+/*
+ * Creates a cothread for the generator. The first call to next64(gen)
+ * will enter the cothread; the entry function must copy the pointer
+ * from the global variable struct gen64 *entry64.
+ *
+ * Use gen->free(gen) to free the cothread.
+ */
+inline void
+gen64_init(struct gen64 *gen, void (*entry)(void))
+{
+	if ((gen->giver = co_create(4096, entry)) == NULL) {
+		/* Perhaps malloc() failed */
+		fputs("co_create: Cannot create cothread\n", stderr);
+		exit(1);
+	}
+	gen->free = gen64_free;
+	entry64 = gen;
+}
+
+
+
+/*
+ * Generates the powers 0**m, 1**m, 2**m, ....
+ */
+void
+powers(struct gen64 *gen, int64_t m)
+{
+	int64_t base, exponent, n, result;
+
+	for (n = 0;; n++) {
+		/*
+		 * This computes result = base**exponent, where
+		 * exponent is a nonnegative integer. The result
+		 * is the product of repeated squares of base.
+		 */
+		base = n;
+		exponent = m;
+		for (result = 1; exponent != 0; exponent >>= 1) {
+			if (exponent & 1) result *= base;
+			base *= base;
+		}
+		yield64(gen, result);
+	}
+	/* NOTREACHED */
+}
+
+/* stuff for squares_without_cubes() */
+#define ENTRY(name, code) static void name(void) { code; }
+ENTRY(enter_squares, powers(entry64, 2))
+ENTRY(enter_cubes, powers(entry64, 3))
+
+struct swc {
+	struct gen64 cubes;
+	struct gen64 squares;
+	void (*old_free)(struct gen64 *);
+};
+
+static void
+swc_free(struct gen64 *gen)
+{
+	struct swc *f = gen->garbage;
+	f->cubes.free(&f->cubes);
+	f->squares.free(&f->squares);
+	f->old_free(gen);
+}
+
+/*
+ * Generates the squares 0**2, 1**2, 2**2, ..., but removes the squares
+ * that equal the cubes 0**3, 1**3, 2**3, ....
+ */
+void
+squares_without_cubes(struct gen64 *gen)
+{
+	struct swc f;
+	int64_t c, s;
+
+	gen64_init(&f.cubes, enter_cubes);
+	c = next64(&f.cubes);
+
+	gen64_init(&f.squares, enter_squares);
+	s = next64(&f.squares);
+
+	/* Allow other cothread to free this generator. */
+	f.old_free = gen->free;
+	gen->garbage = &f;
+	gen->free = swc_free;
+
+	for (;;) {
+		while (c < s)
+			c = next64(&f.cubes);
+		if (c != s)
+			yield64(gen, s);
+		s = next64(&f.squares);
+	}
+	/* NOTREACHED */
+}
+
+ENTRY(enter_squares_without_cubes, squares_without_cubes(entry64))
+
+/*
+ * Look at the sequence of numbers that are squares but not cubes.
+ * Drop the first 20 numbers, then print the next 10 numbers.
+ */
+int
+main()
+{
+	struct gen64 gen;
+	int i;
+
+	gen64_init(&gen, enter_squares_without_cubes);
+
+	for (i = 0; i < 20; i++)
+		next64(&gen);
+	for (i = 0; i < 9; i++)
+		printf("%" PRId64 ", ", next64(&gen));
+	printf("%" PRId64 "\n", next64(&gen));
+
+	gen.free(&gen); /* Free memory. */
+	return 0;
+}