Add nth-prime exercise (#110)

config.json

@@ -306,6 +306,14 @@
         "prerequisites": [],
         "difficulty": 6
       },
+      {
+        "slug": "nth-prime",
+        "name": "Nth Prime",
+        "uuid": "2008083a-fdc5-4a14-8668-6e58f7cd187e",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6
+      },
       {
         "slug": "pascals-triangle",
         "name": "Pascal's Triangle",

exercises/practice/nth-prime/.docs/instructions.md

@@ -0,0 +1,7 @@
+# Instructions
+
+Given a number n, determine what the nth prime is.
+
+By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.
+
+If your language provides methods in the standard library to deal with prime numbers, pretend they don't exist and implement them yourself.

exercises/practice/nth-prime/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "nth_prime.s"
+    ],
+    "test": [
+      "nth_prime_test.c"
+    ],
+    "example": [
+      ".meta/example.s"
+    ]
+  },
+  "blurb": "Given a number n, determine what the nth prime is.",
+  "source": "A variation on Problem 7 at Project Euler",
+  "source_url": "https://projecteuler.net/problem=7"
+}

exercises/practice/nth-prime/.meta/example.s

@@ -0,0 +1,56 @@
+.text
+.globl prime
+
+/* extern uint64_t prime(uint64_t number); */
+prime:
+        cmp     x0, #3
+        blt     .small
+
+        clz     x1, x0                  /* count leading zero bits */
+        mov     x2, #64
+        sub     x1, x2, x1              /* ceil(log2(number + 1)) */
+        mul     x1, x0, x1              /* number * ceil(log2(number + 1)) */
+        lsr     x1, x1, #1              /* divide by 2 */
+        add     x1, x1, #15
+        and     x1, x1, #-16            /* round up to multiple of 16 */
+        mov     x3, sp
+        sub     sp, sp, x1              /* allocate space on stack */
+        mov     x4, #-1
+        mov     x5, sp
+
+.fill:
+        stp     x4, x4, [x3, #-16]!     /* store pair, pre-decrement */
+        cmp     x3, x5
+        bne     .fill
+
+        mov     x4, #1
+        sub     x0, x0, #1              /* we skip the prime 2 */
+
+.search:
+        add     x4, x4, #2              /* candidate prime */
+        lsr     x6, x4, #1              /* divide by 2 */
+        ldrb    w5, [sp, x6]
+        cbz     w5, .search             /* if composite, move on to next candidate */
+
+        sub     x0, x0, #1              /* number of primes required */
+        cbz     x0, .exit
+
+        mul     x5, x4, x4              /* multiple of prime */
+        lsr     x5, x5, #1              /* divide by 2 */
+
+.mark:
+        cmp     x5, x1
+        bhs     .search                 /* unsigned >= */
+
+        strb    wzr, [sp, x5]           /* mark as composite */
+        add     x5, x5, x4
+        b       .mark
+
+.exit:
+        mov     x0, x4
+        add     sp, sp, x1              /* restore original stack pointer */ 
+        ret
+
+.small:
+        add     x0, x0, #1
+        ret

exercises/practice/nth-prime/.meta/tests.toml

@@ -0,0 +1,26 @@
+# 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.
+
+[75c65189-8aef-471a-81de-0a90c728160c]
+description = "first prime"
+
+[2c38804c-295f-4701-b728-56dea34fd1a0]
+description = "second prime"
+
+[56692534-781e-4e8c-b1f9-3e82c1640259]
+description = "sixth prime"
+
+[fce1e979-0edb-412d-93aa-2c744e8f50ff]
+description = "big prime"
+
+[bd0a9eae-6df7-485b-a144-80e13c7d55b2]
+description = "there is no zeroth prime"
+include = false

exercises/practice/nth-prime/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/nth-prime/nth_prime.s

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

exercises/practice/nth-prime/nth_prime_test.c

@@ -0,0 +1,51 @@
+#include "vendor/unity.h"
+
+#include <stdint.h>
+
+extern uint64_t prime(uint64_t number);
+
+void setUp(void) {
+}
+
+void tearDown(void) {
+}
+
+void test_first_prime(void) {
+    TEST_ASSERT_EQUAL_UINT(2, prime(1));
+}
+
+void test_second_prime(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_UINT(3, prime(2));
+}
+
+void test_sixth_prime(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_UINT(13, prime(6));
+}
+
+void test_big_prime(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_UINT(104743, prime(10001));
+}
+
+void test_seventh_prime(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_UINT(17, prime(7));
+}
+
+void test_very_big_prime(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_UINT(821647, prime(65537));
+}
+
+int main(void) {
+    UNITY_BEGIN();
+    RUN_TEST(test_first_prime);
+    RUN_TEST(test_second_prime);
+    RUN_TEST(test_sixth_prime);
+    RUN_TEST(test_big_prime);
+    RUN_TEST(test_seventh_prime);
+    RUN_TEST(test_very_big_prime);
+    return UNITY_END();
+}