Add food-chain exercise (#259)

config.json

@@ -484,6 +484,14 @@
         "prerequisites": [],
         "difficulty": 5
       },
+      {
+        "slug": "food-chain",
+        "name": "Food Chain",
+        "uuid": "5d4da9ec-5b46-4609-b942-6be556884ef3",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6
+      },
       {
         "slug": "luhn",
         "name": "Luhn",

exercises/practice/food-chain/.docs/instructions.md

@@ -0,0 +1,64 @@
+# Instructions
+
+Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'.
+
+While you could copy/paste the lyrics, or read them from a file, this problem is much more interesting if you approach it algorithmically.
+
+This is a [cumulative song][cumulative-song] of unknown origin.
+
+This is one of many common variants.
+
+```text
+I know an old lady who swallowed a fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a spider.
+It wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a bird.
+How absurd to swallow a bird!
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a cat.
+Imagine that, to swallow a cat!
+She swallowed the cat to catch the bird.
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a dog.
+What a hog, to swallow a dog!
+She swallowed the dog to catch the cat.
+She swallowed the cat to catch the bird.
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a goat.
+Just opened her throat and swallowed a goat!
+She swallowed the goat to catch the dog.
+She swallowed the dog to catch the cat.
+She swallowed the cat to catch the bird.
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a cow.
+I don't know how she swallowed a cow!
+She swallowed the cow to catch the goat.
+She swallowed the goat to catch the dog.
+She swallowed the dog to catch the cat.
+She swallowed the cat to catch the bird.
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a horse.
+She's dead, of course!
+```
+
+[cumulative-song]: https://en.wikipedia.org/wiki/Cumulative_song

exercises/practice/food-chain/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "food_chain.asm"
+    ],
+    "test": [
+      "food_chain_test.c"
+    ],
+    "example": [
+      ".meta/example.asm"
+    ]
+  },
+  "blurb": "Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/There_Was_an_Old_Lady_Who_Swallowed_a_Fly"
+}

exercises/practice/food-chain/.meta/example.asm

@@ -0,0 +1,147 @@
+default rel
+
+section .rodata
+
+i_know: db "I know an old lady who swallowed a ", 0
+stop:   db ".", 10, 0
+newline:
+        db 10, 0
+shes_dead:
+        db "She's dead, of course!", 10, 0
+i_dont: db "I don't know why she swallowed the fly. Perhaps she'll die.", 10, 0
+she:    db "She swallowed the ", 0
+to_catch:
+        db " to catch the ", 0
+that:   db " that wriggled and jiggled and tickled inside her", 0
+
+fly:    db "fly", 0
+spider: db "spider", 0
+bird:   db "bird", 0
+cat:    db "cat", 0
+dog:    db "dog", 0
+goat:   db "goat", 0
+cow:    db "cow", 0
+horse:  db "horse", 0
+
+spider2:
+        db "It wriggled and jiggled and tickled inside her.", 10, 0
+bird2:  db "How absurd to swallow a bird!", 10, 0
+cat2:   db "Imagine that, to swallow a cat!", 10, 0
+dog2:   db "What a hog, to swallow a dog!", 10, 0
+goat2:  db "Just opened her throat and swallowed a goat!", 10, 0
+cow2:   db "I don't know how she swallowed a cow!", 10, 0
+
+section .data
+
+animal_array:
+        dq 0
+        dq fly
+        dq spider
+        dq bird
+        dq cat
+        dq dog
+        dq goat
+        dq cow
+        dq horse
+
+animal2_array:
+        dq 0
+        dq 0
+        dq spider2
+        dq bird2
+        dq cat2
+        dq dog2
+        dq goat2
+        dq cow2
+
+
+section .text
+global recite
+
+append:
+        lodsb
+        stosb
+        test    al, al
+        jnz     append
+
+        dec     rdi
+        ret
+
+; extern void recite(char *buffer, int start_verse, int end_verse);
+recite:
+        cld
+        lea     r8, [animal_array]
+        lea     r9, [animal2_array]
+        mov     r10, rsi                ; current verse
+        jmp     .start_verse
+
+.next_verse:
+        inc     r10
+        lea     rsi, [newline]
+        call    append
+
+.start_verse:
+        mov     r11, r10                ; current animal
+        lea     rsi, [i_know]
+        call    append
+
+        mov     rsi, [r8 + r11 * 8]     ; lookup animal_array
+        call    append
+
+        lea     rsi, [stop]
+        call    append
+
+        cmp     r10, 8
+        je      .shes_dead
+
+        cmp     r10, 1
+        je      .i_dont
+
+        mov     rsi, [r9 + r11 * 8]     ; lookup animal2_array
+        call    append
+
+.she:
+        lea     rsi, [she]
+        call    append
+
+        mov     rsi, [r8 + r11 * 8]     ; lookup animal_array
+        call    append
+
+        dec     r11                     ; previous animal
+        lea     rsi, [to_catch]
+        call    append
+
+        mov     rsi, [r8 + r11 * 8]     ; lookup animal_array
+        call    append
+
+        cmp     r11, 2
+        jne     .stop
+
+        lea     rsi, [that]
+        call    append
+
+.stop:
+        lea     rsi, [stop]
+        call    append
+
+        cmp     r11, 1
+        jne     .she                    ; continue inner loop over animals
+
+.i_dont:
+        lea     rsi, [i_dont]
+        call    append
+
+        cmp     r10, rdx
+        jne     .next_verse             ; continue outer loop over verses
+
+        ret
+
+.shes_dead:
+        lea     rsi, [shes_dead]
+        call    append
+
+        ret
+
+%ifidn __OUTPUT_FORMAT__,elf64
+section .note.GNU-stack noalloc noexec nowrite progbits
+%endif

exercises/practice/food-chain/.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.
+
+[751dce68-9412-496e-b6e8-855998c56166]
+description = "fly"
+
+[6c56f861-0c5e-4907-9a9d-b2efae389379]
+description = "spider"
+
+[3edf5f33-bef1-4e39-ae67-ca5eb79203fa]
+description = "bird"
+
+[e866a758-e1ff-400e-9f35-f27f28cc288f]
+description = "cat"
+
+[3f02c30e-496b-4b2a-8491-bc7e2953cafb]
+description = "dog"
+
+[4b3fd221-01ea-46e0-825b-5734634fbc59]
+description = "goat"
+
+[1b707da9-7001-4fac-941f-22ad9c7a65d4]
+description = "cow"
+
+[3cb10d46-ae4e-4d2c-9296-83c9ffc04cdc]
+description = "horse"
+
+[22b863d5-17e4-4d1e-93e4-617329a5c050]
+description = "multiple verses"
+
+[e626b32b-745c-4101-bcbd-3b13456893db]
+description = "full song"

exercises/practice/food-chain/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/food-chain/food_chain.asm

@@ -0,0 +1,13 @@
+default rel
+
+section .data
+
+section .text
+global recite
+recite:
+    ; Provide your implementation here
+    ret
+
+%ifidn __OUTPUT_FORMAT__,elf64
+section .note.GNU-stack noalloc noexec nowrite progbits
+%endif