Add isbn-verifier exercise (#184)

config.json

@@ -235,6 +235,18 @@
           "strings"
         ]
       },
+      {
+        "slug": "isbn-verifier",
+        "name": "Isbn Verifier",
+        "uuid": "f8f770a3-a47b-4404-ae7f-a94af4d8d87f",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4,
+        "topics": [
+          "loops",
+          "strings"
+        ]
+      },
       {
         "slug": "difference-of-squares",
         "name": "Difference of Squares",

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/.gitignore

@@ -0,0 +1,2 @@
+*.o
+tests

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

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "isbn_verifier.asm"
+    ],
+    "test": [
+      "isbn_verifier_test.c"
+    ],
+    "example": [
+      ".meta/example.asm"
+    ]
+  },
+  "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.asm

@@ -0,0 +1,64 @@
+section .text
+global is_valid
+
+; rdi - address of isbn string
+; rax - result (boolean)
+; ecx - weight, counts down to 0
+; dl - current digit
+; r8 - sum
+; r9 - weighted sum
+is_valid:
+    xor rax, rax
+    mov ecx, 10
+    xor rdx, rdx
+    xor r8, r8
+    xor r9, r9
+    jmp .load_byte
+
+.found_x:
+    cmp ecx, 1
+    jne .report_invalid       ; X in non-final position
+    mov dl, 10
+
+.update_sums:
+    add r8, rdx
+    add r9, r8                ; Increase weighed sum using sum
+    dec ecx
+
+.load_byte:
+    mov dl, byte [rdi]        ; Load isbn character
+    inc rdi
+    test dl, dl
+    jz .report                ; Reached end of string
+    cmp dl, '-'
+    je  .load_byte            ; Ignore hyphens
+    test ecx, ecx
+    jz .report_invalid        ; Too many characters
+    cmp dl, 'X'
+    je  .found_x
+    cmp dl, '0'
+    jl .report_invalid
+    cmp dl, '9'
+    jg .report_invalid
+    sub dl, '0'               ; Convert digit to value
+    jmp .update_sums
+
+.report_invalid:
+                              ; rax is already 0
+    ret
+
+.report:
+    test ecx, ecx
+    jnz .report_invalid       ; Reject non-zero weight
+    mov cx, 11
+                              ; dx is already 0
+    mov rax, r9
+    div cx                    ; Divide weighted sum dx:ax by 11
+    cmp dx, 0                 ; Check if remainder is 0
+    sete al                   ; If so, return true, else return false
+                              ; Other bytes of rax are already 0
+    ret
+
+%ifidn __OUTPUT_FORMAT__,elf64
+section .note.GNU-stack noalloc noexec nowrite progbits
+%endif

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

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+AS = nasm
+
+CFLAGS = -g -Wall -Wextra -pedantic -Werror
+LDFLAGS =
+ASFLAGS = -g -F dwarf -Werror
+
+ifeq ($(shell uname -s),Darwin)
+ifeq ($(shell sysctl -n hw.optional.arm64 2>/dev/null),1)
+	ALL_CFLAGS = -target x86_64-apple-darwin
+endif
+	ALL_LDFLAGS = -Wl,-pie -Wl,-fatal_warnings
+	ALL_ASFLAGS = -f macho64 --prefix _
+else
+	ALL_LDFLAGS = -pie -Wl,--fatal-warnings
+	ALL_ASFLAGS = -f elf64
+endif
+
+ALL_CFLAGS += -std=c99 -fPIE -m64 $(CFLAGS)
+ALL_LDFLAGS += $(LDFLAGS)
+ALL_ASFLAGS += $(ASFLAGS)
+
+C_OBJS = $(patsubst %.c,%.o,$(wildcard *.c))
+AS_OBJS = $(patsubst %.asm,%.o,$(wildcard *.asm))
+ALL_OBJS = $(filter-out example.o,$(C_OBJS) $(AS_OBJS) vendor/unity.o)
+
+CC_CMD = $(CC) $(ALL_CFLAGS) -c -o $@ $<
+
+all: tests
+	@./$<
+
+tests: $(ALL_OBJS)
+	@$(CC) $(ALL_CFLAGS) $(ALL_LDFLAGS) -o $@ $(ALL_OBJS)
+
+%.o: %.asm
+	@$(AS) $(ALL_ASFLAGS) -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.asm

@@ -0,0 +1,9 @@
+section .text
+global is_valid
+is_valid:
+    ; Provide your implementation here
+    ret
+
+%ifidn __OUTPUT_FORMAT__,elf64
+section .note.GNU-stack noalloc noexec nowrite progbits
+%endif