Add reverse-string exercise (#86)

config.json

@@ -58,6 +58,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "reverse-string",
+        "name": "Reverse String",
+        "uuid": "90e4cbd3-c4db-4e87-8002-750a67a015a4",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "two-fer",
         "name": "Two-Fer",

exercises/practice/reverse-string/.docs/instructions.md

@@ -0,0 +1,9 @@
+# Instructions
+
+Your task is to reverse a given string.
+
+Some examples:
+
+- Turn `"stressed"` into `"desserts"`.
+- Turn `"strops"` into `"sports"`.
+- Turn `"racecar"` into `"racecar"`.

exercises/practice/reverse-string/.docs/introduction.md

@@ -0,0 +1,5 @@
+# Introduction
+
+Reversing strings (reading them from right to left, rather than from left to right) is a surprisingly common task in programming.
+
+For example, in bioinformatics, reversing the sequence of DNA or RNA strings is often important for various analyses, such as finding complementary strands or identifying palindromic sequences that have biological significance.

exercises/practice/reverse-string/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "reverse_string.s"
+    ],
+    "test": [
+      "reverse_string_test.c"
+    ],
+    "example": [
+      ".meta/example.s"
+    ]
+  },
+  "blurb": "Reverse a given string.",
+  "source": "Introductory challenge to reverse an input string",
+  "source_url": "https://medium.freecodecamp.org/how-to-reverse-a-string-in-javascript-in-3-different-ways-75e4763c68cb"
+}

exercises/practice/reverse-string/.meta/example.s

@@ -0,0 +1,30 @@
+.text
+.globl reverse
+
+/* extern void reverse(char *str); */
+reverse:
+        mov     x1, x0
+
+.scan:
+        ldrb    w2, [x1], #1            /* load byte, post-increment */
+        cbnz    w2, .scan
+
+        sub     x1, x1, #1
+        cmp     x1, x0
+        beq     .done                   /* zero length string */
+
+.reverse:
+        sub     x1, x1, #1
+        cmp     x1, x0
+        beq     .done                   /* middle byte of odd length string */
+
+        ldrb    w2, [x1]
+        ldrb    w3, [x0]
+        strb    w3, [x1]
+        strb    w2, [x0], #1            /* store byte, post-increment */
+        cmp     x1, x0
+        bne     .reverse
+                                        /* middle bytes of even length string */
+
+.done:
+        ret

exercises/practice/reverse-string/.meta/tests.toml

@@ -0,0 +1,40 @@
+# 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.
+
+[c3b7d806-dced-49ee-8543-933fd1719b1c]
+description = "an empty string"
+
+[01ebf55b-bebb-414e-9dec-06f7bb0bee3c]
+description = "a word"
+
+[0f7c07e4-efd1-4aaa-a07a-90b49ce0b746]
+description = "a capitalized word"
+
+[71854b9c-f200-4469-9f5c-1e8e5eff5614]
+description = "a sentence with punctuation"
+
+[1f8ed2f3-56f3-459b-8f3e-6d8d654a1f6c]
+description = "a palindrome"
+
+[b9e7dec1-c6df-40bd-9fa3-cd7ded010c4c]
+description = "an even-sized word"
+
+[1bed0f8a-13b0-4bd3-9d59-3d0593326fa2]
+description = "wide characters"
+include = false
+
+[93d7e1b8-f60f-4f3c-9559-4056e10d2ead]
+description = "grapheme cluster with pre-combined form"
+include = false
+
+[1028b2c1-6763-4459-8540-2da47ca512d9]
+description = "grapheme clusters"
+include = false

exercises/practice/reverse-string/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/reverse-string/reverse_string.s

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

exercises/practice/reverse-string/reverse_string_test.c

@@ -0,0 +1,61 @@
+#include "vendor/unity.h"
+
+extern void reverse(char *str);
+
+void setUp(void) {
+}
+
+void tearDown(void) {
+}
+
+void test_an_empty_string(void) {
+    char str[] = "";
+    reverse(str);
+    TEST_ASSERT_EQUAL_STRING("", str);
+}
+
+void test_a_word(void) {
+    TEST_IGNORE();
+    char str[] = "robot";
+    reverse(str);
+    TEST_ASSERT_EQUAL_STRING("tobor", str);
+}
+
+void test_a_capitalized_word(void) {
+    TEST_IGNORE();
+    char str[] = "Ramen";
+    reverse(str);
+    TEST_ASSERT_EQUAL_STRING("nemaR", str);
+}
+
+void test_a_sentence_with_punctuation(void) {
+    TEST_IGNORE();
+    char str[] = "I'm hungry!";
+    reverse(str);
+    TEST_ASSERT_EQUAL_STRING("!yrgnuh m'I", str);
+}
+
+void test_a_palindrome(void) {
+    TEST_IGNORE();
+    char str[] = "racecar";
+    reverse(str);
+    TEST_ASSERT_EQUAL_STRING("racecar", str);
+}
+
+void test_an_evensized_word(void) {
+    TEST_IGNORE();
+    char str[] = "drawer";
+    reverse(str);
+    TEST_ASSERT_EQUAL_STRING("reward", str);
+}
+
+int main(void) {
+    UNITY_BEGIN();
+    RUN_TEST(test_an_empty_string);
+    RUN_TEST(test_a_word);
+    RUN_TEST(test_a_capitalized_word);
+    RUN_TEST(test_a_sentence_with_punctuation);
+    RUN_TEST(test_a_palindrome);
+    RUN_TEST(test_an_evensized_word);
+    return UNITY_END();
+}