Add luhn exercise (#246)

config.json

@@ -460,6 +460,14 @@
           "arrays"
         ]
       },
+      {
+        "slug": "luhn",
+        "name": "Luhn",
+        "uuid": "0dd26cf2-d613-4a03-93a3-49d2960d2154",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6
+      },
       {
         "slug": "pascals-triangle",
         "name": "Pascal's Triangle",

exercises/practice/luhn/.docs/instructions.md

@@ -0,0 +1,65 @@
+# Instructions
+
+Given a number determine whether or not it is valid per the Luhn formula.
+
+The [Luhn algorithm][luhn] is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers and Canadian Social Insurance Numbers.
+
+The task is to check if a given string is valid.
+
+## Validating a Number
+
+Strings of length 1 or less are not valid.
+Spaces are allowed in the input, but they should be stripped before checking.
+All other non-digit characters are disallowed.
+
+### Example 1: valid credit card number
+
+```text
+4539 3195 0343 6467
+```
+
+The first step of the Luhn algorithm is to double every second digit, starting from the right.
+We will be doubling
+
+```text
+4539 3195 0343 6467
+↑ ↑  ↑ ↑  ↑ ↑  ↑ ↑  (double these)
+```
+
+If doubling the number results in a number greater than 9 then subtract 9 from the product.
+The results of our doubling:
+
+```text
+8569 6195 0383 3437
+```
+
+Then sum all of the digits:
+
+```text
+8+5+6+9+6+1+9+5+0+3+8+3+3+4+3+7 = 80
+```
+
+If the sum is evenly divisible by 10, then the number is valid.
+This number is valid!
+
+### Example 2: invalid credit card number
+
+```text
+8273 1232 7352 0569
+```
+
+Double the second digits, starting from the right
+
+```text
+7253 2262 5312 0539
+```
+
+Sum the digits
+
+```text
+7+2+5+3+2+2+6+2+5+3+1+2+0+5+3+9 = 57
+```
+
+57 is not evenly divisible by 10, so this number is not valid.
+
+[luhn]: https://en.wikipedia.org/wiki/Luhn_algorithm

exercises/practice/luhn/.gitignore

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

exercises/practice/luhn/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "luhn.asm"
+    ],
+    "test": [
+      "luhn_test.c"
+    ],
+    "example": [
+      ".meta/example.asm"
+    ]
+  },
+  "blurb": "Given a number determine whether or not it is valid per the Luhn formula.",
+  "source": "The Luhn Algorithm on Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Luhn_algorithm"
+}

exercises/practice/luhn/.meta/example.asm

@@ -0,0 +1,68 @@
+section .text
+global valid
+valid:
+    cld ; rsi will be incremented with each lodsb
+    mov rsi, rdi
+    dec rdi ; the address immediately before the first character
+    xor rax, rax
+    xor rcx, rcx ; number of digits read
+    xor r8, r8 ; total
+    mov r10, 10
+
+.seek_end:
+    lodsb
+    test al, al
+    jnz .seek_end
+
+    sub rsi, 2 ; the address immediately before the null character
+    std ; rsi will be decremented with each lodsb
+    jmp .check_end
+
+.read:
+    lodsb
+    cmp al, ' '
+    je .check_end
+
+    sub al, '0'
+    cmp al, 10
+    jae .invalid
+
+    inc rcx
+    test rcx, 1
+    jnz .odd
+
+    shl rax, 1
+    cmp rax, 9
+    jb .odd
+
+    sub rax, 9
+
+.odd:
+    add r8, rax
+
+.check_end:
+    cmp rsi, rdi
+    jne .read
+
+    cmp rcx, 1
+    jbe .invalid
+
+    mov rax, r8
+    xor rdx, rdx
+    div r10
+    test rdx, rdx
+    jnz .invalid
+
+.valid:
+    cld
+    mov rax, 1
+    ret
+
+.invalid:
+    cld
+    xor rax, rax
+    ret
+
+%ifidn __OUTPUT_FORMAT__,elf64
+section .note.GNU-stack noalloc noexec nowrite progbits
+%endif

exercises/practice/luhn/.meta/tests.toml

@@ -0,0 +1,76 @@
+# 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.
+
+[792a7082-feb7-48c7-b88b-bbfec160865e]
+description = "single digit strings can not be valid"
+
+[698a7924-64d4-4d89-8daa-32e1aadc271e]
+description = "a single zero is invalid"
+
+[73c2f62b-9b10-4c9f-9a04-83cee7367965]
+description = "a simple valid SIN that remains valid if reversed"
+
+[9369092e-b095-439f-948d-498bd076be11]
+description = "a simple valid SIN that becomes invalid if reversed"
+
+[8f9f2350-1faf-4008-ba84-85cbb93ffeca]
+description = "a valid Canadian SIN"
+
+[1cdcf269-6560-44fc-91f6-5819a7548737]
+description = "invalid Canadian SIN"
+
+[656c48c1-34e8-4e60-9a5a-aad8a367810a]
+description = "invalid credit card"
+
+[20e67fad-2121-43ed-99a8-14b5b856adb9]
+description = "invalid long number with an even remainder"
+
+[7e7c9fc1-d994-457c-811e-d390d52fba5e]
+description = "invalid long number with a remainder divisible by 5"
+
+[ad2a0c5f-84ed-4e5b-95da-6011d6f4f0aa]
+description = "valid number with an even number of digits"
+
+[ef081c06-a41f-4761-8492-385e13c8202d]
+description = "valid number with an odd number of spaces"
+
+[bef66f64-6100-4cbb-8f94-4c9713c5e5b2]
+description = "valid strings with a non-digit added at the end become invalid"
+
+[2177e225-9ce7-40f6-b55d-fa420e62938e]
+description = "valid strings with punctuation included become invalid"
+
+[ebf04f27-9698-45e1-9afe-7e0851d0fe8d]
+description = "valid strings with symbols included become invalid"
+
+[08195c5e-ce7f-422c-a5eb-3e45fece68ba]
+description = "single zero with space is invalid"
+
+[12e63a3c-f866-4a79-8c14-b359fc386091]
+description = "more than a single zero is valid"
+
+[ab56fa80-5de8-4735-8a4a-14dae588663e]
+description = "input digit 9 is correctly converted to output digit 9"
+
+[b9887ee8-8337-46c5-bc45-3bcab51bc36f]
+description = "very long input is valid"
+
+[8a7c0e24-85ea-4154-9cf1-c2db90eabc08]
+description = "valid luhn with an odd number of digits and non zero first digit"
+
+[39a06a5a-5bad-4e0f-b215-b042d46209b1]
+description = "using ascii value for non-doubled non-digit isn't allowed"
+
+[f94cf191-a62f-4868-bc72-7253114aa157]
+description = "using ascii value for doubled non-digit isn't allowed"
+
+[8b72ad26-c8be-49a2-b99c-bcc3bf631b33]
+description = "non-numeric, non-space char in the middle with a sum that's divisible by 10 isn't allowed"

exercises/practice/luhn/Makefile

@@ -0,0 +1,46 @@
+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
+	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/luhn/luhn.asm

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