Add collatz-conjecture exercise (#67)

config.json

@@ -42,6 +42,14 @@
           "strings"
         ]
       },
+      {
+        "slug": "collatz-conjecture",
+        "name": "Collatz Conjecture",
+        "uuid": "926ee852-050e-4d4e-81c2-122a564dd664",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "leap",
         "name": "Leap",

exercises/practice/collatz-conjecture/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+The Collatz Conjecture or 3x+1 problem can be summarized as follows:
+
+Take any positive integer n.
+If n is even, divide n by 2 to get n / 2.
+If n is odd, multiply n by 3 and add 1 to get 3n + 1.
+Repeat the process indefinitely.
+The conjecture states that no matter which number you start with, you will always reach 1 eventually.
+
+Given a number n, return the number of steps required to reach 1.
+
+## Examples
+
+Starting with n = 12, the steps would be as follows:
+
+0. 12
+1. 6
+2. 3
+3. 10
+4. 5
+5. 16
+6. 8
+7. 4
+8. 2
+9. 1
+
+Resulting in 9 steps.
+So for input n = 12, the return value would be 9.

exercises/practice/collatz-conjecture/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "collatz_conjecture.s"
+    ],
+    "test": [
+      "collatz_conjecture_test.c"
+    ],
+    "example": [
+      ".meta/example.s"
+    ]
+  },
+  "blurb": "Calculate the number of steps to reach 1 using the Collatz conjecture.",
+  "source": "An unsolved problem in mathematics named after mathematician Lothar Collatz",
+  "source_url": "https://en.wikipedia.org/wiki/3x_%2B_1_problem"
+}

exercises/practice/collatz-conjecture/.meta/example.s

@@ -0,0 +1,32 @@
+.text
+.globl steps
+
+/* extern int steps(int number); */
+steps:
+        mov     x1, #1
+        cmp     x0, x1
+        blt     .invalid
+
+        mov     x2, x0                  /* current number */
+        mov     x3, #3
+        mov     x0, #0                  /* step count */
+
+.loop:
+        cmp     x2, x1
+        beq     .return
+
+        tbz     x2, #0, .even           /* jump ahead if low bit is clear */
+
+        madd    x2, x3, x2, x1          /* 3 * number + 1 */
+        add     x0, x0, #1              /* increment step count */
+
+.even:
+        lsr     x2, x2, #1              /* number / 2 */
+        add     x0, x0, #1              /* increment step count */
+        b       .loop
+
+.invalid:
+        mov     x0, #-1
+
+.return:
+        ret

exercises/practice/collatz-conjecture/.meta/tests.toml

@@ -0,0 +1,38 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[540a3d51-e7a6-47a5-92a3-4ad1838f0bfd]
+description = "zero steps for one"
+
+[3d76a0a6-ea84-444a-821a-f7857c2c1859]
+description = "divide if even"
+
+[754dea81-123c-429e-b8bc-db20b05a87b9]
+description = "even and odd steps"
+
+[ecfd0210-6f85-44f6-8280-f65534892ff6]
+description = "large number of even and odd steps"
+
+[7d4750e6-def9-4b86-aec7-9f7eb44f95a3]
+description = "zero is an error"
+include = false
+
+[2187673d-77d6-4543-975e-66df6c50e2da]
+description = "zero is an error"
+reimplements = "7d4750e6-def9-4b86-aec7-9f7eb44f95a3"
+
+[c6c795bf-a288-45e9-86a1-841359ad426d]
+description = "negative value is an error"
+include = false
+
+[ec11f479-56bc-47fd-a434-bcd7a31a7a2e]
+description = "negative value is an error"
+reimplements = "c6c795bf-a288-45e9-86a1-841359ad426d"

exercises/practice/collatz-conjecture/Makefile

@@ -0,0 +1,36 @@
+AS = aarch64-linux-gnu-as
+CC = aarch64-linux-gnu-gcc
+
+CFLAGS = -g -Wall -Wextra -pedantic -Werror
+LDFLAGS =
+
+ALL_LDFLAGS = -pie -Wl,--fatal-warnings
+
+ALL_CFLAGS = -std=c99 -fPIE $(CFLAGS)
+ALL_LDFLAGS += $(LDFLAGS)
+
+C_OBJS = $(patsubst %.c,%.o,$(wildcard *.c))
+AS_OBJS = $(patsubst %.s,%.o,$(wildcard *.s))
+ALL_OBJS = $(filter-out example.o,$(C_OBJS) $(AS_OBJS) vendor/unity.o)
+
+CC_CMD = $(CC) $(ALL_CFLAGS) -c -o $@ $<
+
+all: tests
+	qemu-aarch64 -L /usr/aarch64-linux-gnu ./$<
+
+tests: $(ALL_OBJS)
+	@$(CC) $(ALL_CFLAGS) $(ALL_LDFLAGS) -o $@ $(ALL_OBJS)
+
+%.o: %.s
+	@$(AS) -o $@ $<
+
+%.o: %.c
+	@$(CC_CMD)
+
+vendor/unity.o: vendor/unity.c vendor/unity.h vendor/unity_internals.h
+	@$(CC_CMD)
+
+clean:
+	@rm -f *.o vendor/*.o tests
+
+.PHONY: all clean

exercises/practice/collatz-conjecture/collatz_conjecture.s

@@ -0,0 +1,5 @@
+.text
+.globl steps
+
+steps:
+    ret

exercises/practice/collatz-conjecture/collatz_conjecture_test.c

@@ -0,0 +1,65 @@
+#include "vendor/unity.h"
+
+#include <stdint.h>
+
+#define ERROR_VALUE -1
+
+extern int steps(int64_t number);
+
+void setUp(void) {
+}
+
+void tearDown(void) {
+}
+
+void test_zero_steps_for_one(void) {
+    TEST_ASSERT_EQUAL_INT(0, steps(1));
+}
+
+void test_divide_if_even(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(4, steps(16));
+}
+
+void test_even_and_odd_steps(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(9, steps(12));
+}
+
+void test_large_number_of_even_and_odd_steps(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(152, steps(1000000));
+}
+
+void test_zero_is_an_error(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(-1, steps(0));
+}
+
+void test_negative_value_is_an_error(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(-1, steps(-15));
+}
+
+void test_large_positive(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(817, steps(2037066081));
+}
+
+void test_large_negative(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(-1, steps(-7001002003));
+}
+
+int main(void) {
+    UNITY_BEGIN();
+    RUN_TEST(test_zero_steps_for_one);
+    RUN_TEST(test_divide_if_even);
+    RUN_TEST(test_even_and_odd_steps);
+    RUN_TEST(test_large_number_of_even_and_odd_steps);
+    RUN_TEST(test_zero_is_an_error);
+    RUN_TEST(test_negative_value_is_an_error);
+    RUN_TEST(test_large_positive);
+    RUN_TEST(test_large_negative);
+    return UNITY_END();
+}