Add isbn-verifier exercise (#74)

config.json

@@ -105,6 +105,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 3
+      },
+      {
+        "slug": "isbn-verifier",
+        "name": "ISBN Verifier",
+        "uuid": "b8d74744-3783-4c5e-9cc2-3efcb9aae236",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
       }
     ]
   },

exercises/practice/isbn-verifier/.docs/instructions.md

@@ -0,0 +1,42 @@
+# Instructions
+
+The [ISBN-10 verification process][isbn-verification] is used to validate book identification numbers.
+These normally contain dashes and look like: `3-598-21508-8`
+
+## ISBN
+
+The ISBN-10 format is 9 digits (0 to 9) plus one check character (either a digit or an X only).
+In the case the check character is an X, this represents the value '10'.
+These may be communicated with or without hyphens, and can be checked for their validity by the following formula:
+
+```text
+(d₁ * 10 + d₂ * 9 + d₃ * 8 + d₄ * 7 + d₅ * 6 + d₆ * 5 + d₇ * 4 + d₈ * 3 + d₉ * 2 + d₁₀ * 1) mod 11 == 0
+```
+
+If the result is 0, then it is a valid ISBN-10, otherwise it is invalid.
+
+## Example
+
+Let's take the ISBN-10 `3-598-21508-8`.
+We plug it in to the formula, and get:
+
+```text
+(3 * 10 + 5 * 9 + 9 * 8 + 8 * 7 + 2 * 6 + 1 * 5 + 5 * 4 + 0 * 3 + 8 * 2 + 8 * 1) mod 11 == 0
+```
+
+Since the result is 0, this proves that our ISBN is valid.
+
+## Task
+
+Given a string the program should check if the provided string is a valid ISBN-10.
+Putting this into place requires some thinking about preprocessing/parsing of the string prior to calculating the check digit for the ISBN.
+
+The program should be able to verify ISBN-10 both with and without separating dashes.
+
+## Caveats
+
+Converting from strings to numbers can be tricky in certain languages.
+Now, it's even trickier since the check digit of an ISBN-10 may be 'X' (representing '10').
+For instance `3-598-21507-X` is a valid ISBN-10.
+
+[isbn-verification]: https://en.wikipedia.org/wiki/International_Standard_Book_Number

exercises/practice/isbn-verifier/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "isbn_verifier.s"
+    ],
+    "test": [
+      "isbn_verifier_test.c"
+    ],
+    "example": [
+      ".meta/example.s"
+    ]
+  },
+  "blurb": "Check if a given string is a valid ISBN-10 number.",
+  "source": "Converting a string into a number and some basic processing utilizing a relatable real world example.",
+  "source_url": "https://en.wikipedia.org/wiki/International_Standard_Book_Number#ISBN-10_check_digit_calculation"
+}

exercises/practice/isbn-verifier/.meta/example.s

@@ -0,0 +1,48 @@
+.text
+.globl is_valid
+
+/* extern int is_valid(const char *isbn); */
+is_valid:
+        mov     x1, #10                 /* number of digits remaining */
+        mov     x4, #0                  /* sum */
+        mov     x5, #0                  /* weighted sum */
+
+.loop:
+        ldrb    w2, [x0], #1            /* load byte, with post-increment */
+        cbz     x2, .end
+
+        cmp     x2, #45                 /* hyphen */
+        beq     .loop
+
+        sub     x1, x1, #1              /* decrement number of digits remaining */
+        sub     x3, x2, #48             /* '0' */
+        cmp     x3, #10
+        bhs     .non_digit              /* unsigned >= */
+
+.add:
+        add     x4, x4, x3
+        add     x5, x5, x4
+        b       .loop
+
+.non_digit:
+        tst     x1, x1
+        bne     .reject
+
+        mov     x3, #10
+        cmp     x2, #88                 /* 'X' */
+        beq     .add
+
+.reject:
+        mov     x0, #0
+        ret
+
+.end:
+        tst     x1, x1
+        bne     .reject
+
+        mov     x1, #11
+        udiv    x4, x5, x1              /* weighted sum / 11 */
+        msub    x3, x4, x1, x5          /* weighted sum % 11 */
+        tst     x3, x3
+        cset    x0, eq
+        ret

exercises/practice/isbn-verifier/.meta/tests.toml

@@ -0,0 +1,67 @@
+# 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.
+
+[0caa3eac-d2e3-4c29-8df8-b188bc8c9292]
+description = "valid isbn"
+
+[19f76b53-7c24-45f8-87b8-4604d0ccd248]
+description = "invalid isbn check digit"
+
+[4164bfee-fb0a-4a1c-9f70-64c6a1903dcd]
+description = "valid isbn with a check digit of 10"
+
+[3ed50db1-8982-4423-a993-93174a20825c]
+description = "check digit is a character other than X"
+
+[9416f4a5-fe01-4b61-a07b-eb75892ef562]
+description = "invalid check digit in isbn is not treated as zero"
+
+[c19ba0c4-014f-4dc3-a63f-ff9aefc9b5ec]
+description = "invalid character in isbn is not treated as zero"
+
+[28025280-2c39-4092-9719-f3234b89c627]
+description = "X is only valid as a check digit"
+
+[f6294e61-7e79-46b3-977b-f48789a4945b]
+description = "valid isbn without separating dashes"
+
+[185ab99b-3a1b-45f3-aeec-b80d80b07f0b]
+description = "isbn without separating dashes and X as check digit"
+
+[7725a837-ec8e-4528-a92a-d981dd8cf3e2]
+description = "isbn without check digit and dashes"
+
+[47e4dfba-9c20-46ed-9958-4d3190630bdf]
+description = "too long isbn and no dashes"
+
+[737f4e91-cbba-4175-95bf-ae630b41fb60]
+description = "too short isbn"
+
+[5458a128-a9b6-4ff8-8afb-674e74567cef]
+description = "isbn without check digit"
+
+[70b6ad83-d0a2-4ca7-a4d5-a9ab731800f7]
+description = "check digit of X should not be used for 0"
+
+[94610459-55ab-4c35-9b93-ff6ea1a8e562]
+description = "empty isbn"
+
+[7bff28d4-d770-48cc-80d6-b20b3a0fb46c]
+description = "input is 9 characters"
+
+[ed6e8d1b-382c-4081-8326-8b772c581fec]
+description = "invalid characters are not ignored after checking length"
+
+[daad3e58-ce00-4395-8a8e-e3eded1cdc86]
+description = "invalid characters are not ignored before checking length"
+
+[fb5e48d8-7c03-4bfb-a088-b101df16fdc3]
+description = "input is too long but contains a valid isbn"

exercises/practice/isbn-verifier/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/isbn-verifier/isbn_verifier.s

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

exercises/practice/isbn-verifier/isbn_verifier_test.c

@@ -0,0 +1,127 @@
+#include "vendor/unity.h"
+
+extern int is_valid(const char *isbn);
+
+void setUp(void) {
+}
+
+void tearDown(void) {
+}
+
+void test_valid_isbn(void) {
+    TEST_ASSERT_TRUE(is_valid("3-598-21508-8"));
+}
+
+void test_invalid_isbn_check_digit(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("3-598-21508-9"));
+}
+
+void test_valid_isbn_with_a_check_digit_of_10(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_TRUE(is_valid("3-598-21507-X"));
+}
+
+void test_check_digit_is_a_character_other_than_x(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("3-598-21507-A"));
+}
+
+void test_invalid_check_digit_in_isbn_is_not_treated_as_zero(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("4-598-21507-B"));
+}
+
+void test_invalid_character_in_isbn_is_not_treated_as_zero(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("3-598-P1581-X"));
+}
+
+void test_x_is_only_valid_as_a_check_digit(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("3-598-2X507-9"));
+}
+
+void test_valid_isbn_without_separating_dashes(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_TRUE(is_valid("3598215088"));
+}
+
+void test_isbn_without_separating_dashes_and_x_as_check_digit(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_TRUE(is_valid("359821507X"));
+}
+
+void test_isbn_without_check_digit_and_dashes(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("359821507"));
+}
+
+void test_too_long_isbn_and_no_dashes(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("3598215078X"));
+}
+
+void test_too_short_isbn(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("00"));
+}
+
+void test_isbn_without_check_digit(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("3-598-21507"));
+}
+
+void test_check_digit_of_x_should_not_be_used_for_0(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("3-598-21515-X"));
+}
+
+void test_empty_isbn(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid(""));
+}
+
+void test_input_is_9_characters(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("134456729"));
+}
+
+void test_invalid_characters_are_not_ignored_after_checking_length(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("3132P34035"));
+}
+
+void test_invalid_characters_are_not_ignored_before_checking_length(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("3598P215088"));
+}
+
+void test_input_is_too_long_but_contains_a_valid_isbn(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_FALSE(is_valid("98245726788"));
+}
+
+int main(void) {
+    UNITY_BEGIN();
+    RUN_TEST(test_valid_isbn);
+    RUN_TEST(test_invalid_isbn_check_digit);
+    RUN_TEST(test_valid_isbn_with_a_check_digit_of_10);
+    RUN_TEST(test_check_digit_is_a_character_other_than_x);
+    RUN_TEST(test_invalid_check_digit_in_isbn_is_not_treated_as_zero);
+    RUN_TEST(test_invalid_character_in_isbn_is_not_treated_as_zero);
+    RUN_TEST(test_x_is_only_valid_as_a_check_digit);
+    RUN_TEST(test_valid_isbn_without_separating_dashes);
+    RUN_TEST(test_isbn_without_separating_dashes_and_x_as_check_digit);
+    RUN_TEST(test_isbn_without_check_digit_and_dashes);
+    RUN_TEST(test_too_long_isbn_and_no_dashes);
+    RUN_TEST(test_too_short_isbn);
+    RUN_TEST(test_isbn_without_check_digit);
+    RUN_TEST(test_check_digit_of_x_should_not_be_used_for_0);
+    RUN_TEST(test_empty_isbn);
+    RUN_TEST(test_input_is_9_characters);
+    RUN_TEST(test_invalid_characters_are_not_ignored_after_checking_length);
+    RUN_TEST(test_invalid_characters_are_not_ignored_before_checking_length);
+    RUN_TEST(test_input_is_too_long_but_contains_a_valid_isbn);
+    return UNITY_END();
+}