Add two-fer exercise

config.json

@@ -58,6 +58,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "two-fer",
+        "name": "Two-Fer",
+        "uuid": "4f341658-cc4d-406b-98be-1839d446baf6",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "bob",
         "name": "Bob",

exercises/practice/two-fer/.docs/instructions.md

@@ -0,0 +1,24 @@
+# Instructions
+
+Your task is to determine what you will say as you give away the extra cookie.
+
+If you know the person's name (e.g. if they're named Do-yun), then you will say:
+
+```text
+One for Do-yun, one for me.
+```
+
+If you don't know the person's name, you will say _you_ instead.
+
+```text
+One for you, one for me.
+```
+
+Here are some examples:
+
+| Name   | Dialogue                    |
+| :----- | :-------------------------- |
+| Alice  | One for Alice, one for me.  |
+| Bohdan | One for Bohdan, one for me. |
+|        | One for you, one for me.    |
+| Zaphod | One for Zaphod, one for me. |

exercises/practice/two-fer/.docs/introduction.md

@@ -0,0 +1,8 @@
+# Introduction
+
+In some English accents, when you say "two for" quickly, it sounds like "two fer".
+Two-for-one is a way of saying that if you buy one, you also get one for free.
+So the phrase "two-fer" often implies a two-for-one offer.
+
+Imagine a bakery that has a holiday offer where you can buy two cookies for the price of one ("two-fer one!").
+You take the offer and (very generously) decide to give the extra cookie to someone else in the queue.

exercises/practice/two-fer/.meta/config.json

@@ -0,0 +1,18 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "two_fer.s"
+    ],
+    "test": [
+      "two_fer_test.c"
+    ],
+    "example": [
+      ".meta/example.s"
+    ]
+  },
+  "blurb": "Create a sentence of the form \"One for X, one for me.\".",
+  "source_url": "https://github.com/exercism/problem-specifications/issues/757"
+}

exercises/practice/two-fer/.meta/example.s

@@ -0,0 +1,36 @@
+.section .rodata
+prefix: .string "One for "
+you: .string "you"
+suffix: .string ", one for me."
+
+.macro LOAD str
+        adrp    x2, \str
+        add     x2, x2, :lo12:\str
+.endm
+
+.macro APPEND str
+
+.copy_\str:
+        ldrb    w3, [x2], #1            /* load byte, with post-increment */
+        strb    w3, [x0], #1            /* store byte, post-increment */
+        cbnz    w3, .copy_\str
+
+        sub     x0, x0, #1
+.endm
+
+.text
+.globl two_fer
+
+/* extern void two_fer(char *buffer, const char *name); */
+two_fer:
+        LOAD    prefix
+        APPEND  prefix
+
+        LOAD    you
+        tst     x1, x1
+        csel    x2, x1, x2, ne          /* name if non-null, otherwise you */
+        APPEND  you
+
+        LOAD    suffix
+        APPEND  suffix
+        ret

exercises/practice/two-fer/.meta/tests.toml

@@ -0,0 +1,19 @@
+# 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.
+
+[1cf3e15a-a3d7-4a87-aeb3-ba1b43bc8dce]
+description = "no name given"
+
+[b4c6dbb8-b4fb-42c2-bafd-10785abe7709]
+description = "a name given"
+
+[3549048d-1a6e-4653-9a79-b0bda163e8d5]
+description = "another name given"

exercises/practice/two-fer/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/two-fer/two_fer.s

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

exercises/practice/two-fer/two_fer_test.c

@@ -0,0 +1,44 @@
+#include "vendor/unity.h"
+
+#include <stddef.h>
+
+#define BUFFER_SIZE 80
+
+extern void two_fer(char *buffer, const char *name);
+
+void setUp(void) {
+}
+
+void tearDown(void) {
+}
+
+void test_no_name_given(void) {
+    char buffer[BUFFER_SIZE];
+
+    two_fer(buffer, NULL);
+    TEST_ASSERT_EQUAL_STRING("One for you, one for me.", buffer);
+}
+
+void test_a_name_given(void) {
+    TEST_IGNORE();
+    char buffer[BUFFER_SIZE];
+
+    two_fer(buffer, "Alice");
+    TEST_ASSERT_EQUAL_STRING("One for Alice, one for me.", buffer);
+}
+
+void test_another_name_given(void) {
+    TEST_IGNORE();
+    char buffer[BUFFER_SIZE];
+
+    two_fer(buffer, "Bob");
+    TEST_ASSERT_EQUAL_STRING("One for Bob, one for me.", buffer);
+}
+
+int main(void) {
+    UNITY_BEGIN();
+    RUN_TEST(test_no_name_given);
+    RUN_TEST(test_a_name_given);
+    RUN_TEST(test_another_name_given);
+    return UNITY_END();
+}