Add food-chain exercise (#135)

config.json

@@ -354,6 +354,14 @@
         "prerequisites": [],
         "difficulty": 5
       },
+      {
+        "slug": "food-chain",
+        "name": "Food Chain",
+        "uuid": "bd684e71-75b9-4d31-8775-cb93eeb6dea0",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "house",
         "name": "House",

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.s"
+    ],
+    "test": [
+      "food_chain_test.c"
+    ],
+    "example": [
+      ".meta/example.s"
+    ]
+  },
+  "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.s

@@ -0,0 +1,147 @@
+.data
+
+i_know: .string "I know an old lady who swallowed a "
+stop:   .string ".\n"
+shes:   .string "She's dead, of course!\n"
+i_dont: .string "I don't know why she swallowed the fly. Perhaps she'll die.\n"
+she:    .string "She swallowed the "
+to:     .string " to catch the "
+that:   .string " that wriggled and jiggled and tickled inside her"
+
+fly:    .string "fly"
+spider: .string "spider"
+bird:   .string "bird"
+cat:    .string "cat"
+dog:    .string "dog"
+goat:   .string "goat"
+cow:    .string "cow"
+horse:  .string "horse"
+
+spider2:
+        .string "It wriggled and jiggled and tickled inside her.\n"
+bird2:  .string "How absurd to swallow a bird!\n"
+cat2:   .string "Imagine that, to swallow a cat!\n"
+dog2:   .string "What a hog, to swallow a dog!\n"
+goat2:  .string "Just opened her throat and swallowed a goat!\n"
+cow2:   .string "I don't know how she swallowed a cow!\n"
+
+animal_array:
+        .dword 0
+        .dword fly
+        .dword spider
+        .dword bird
+        .dword cat
+        .dword dog
+        .dword goat
+        .dword cow
+        .dword horse
+
+animal2_array:
+        .dword 0
+        .dword 0
+        .dword spider2
+        .dword bird2
+        .dword cat2
+        .dword dog2
+        .dword goat2
+        .dword cow2
+
+.macro LOAD register, label
+        adrp    \register, \label
+        add     \register, \register, :lo12:\label
+.endm
+
+.macro APPEND str
+
+.copy_\str:
+        ldrb    w15, [x14], #1          /* load byte, with post-increment */
+        strb    w15, [x0], #1           /* store byte, post-increment */
+        cbnz    w15, .copy_\str
+
+        sub     x0, x0, #1
+.endm
+
+.text
+.globl recite
+
+/* extern void recite(char *buffer, int start_verse, int end_verse); */
+recite:
+        LOAD    x3, i_know
+        LOAD    x4, stop
+        LOAD    x5, shes
+        LOAD    x6, i_dont
+        LOAD    x7, she
+        LOAD    x8, to
+        LOAD    x9, that
+        LOAD    x10, animal_array                    
+        LOAD    x11, animal2_array
+
+        lsl     x1, x1, #3
+        lsl     x2, x2, #3
+
+.verse:
+        mov     x14, x3
+        APPEND  i_know
+
+        ldr     x14, [x10, x1]
+        APPEND  animal
+
+        mov     x14, x4
+        APPEND  stop
+
+        cmp     x1, #64
+        beq     .shes
+
+        cmp     x1, #8
+        beq     .i_dont
+
+        ldr     x14, [x11, x1]
+        APPEND  second
+
+        mov     x13, x1
+
+.reason:
+        mov     x14, x7
+        APPEND  she
+
+        ldr     x14, [x10, x13]
+        APPEND  animal2
+
+        mov     x14, x8
+        APPEND  to
+
+        sub     x13, x13, #8
+        ldr     x14, [x10, x13]
+        APPEND  animal3
+
+        cmp     x13, #16
+        bne     .stop
+
+        mov     x14, x9
+        APPEND  that
+
+.stop:  
+        mov     x14, x4
+        APPEND  stop2
+
+        cmp     x13, #8
+        bne     .reason
+
+.i_dont:
+        mov     x14, x6
+        APPEND  i_dont
+
+        cmp     x1, x2
+        beq     .return
+
+        add     x1, x1, #8
+        mov     w15, #'\n'
+        strb    w15, [x0], #1
+        b       .verse
+
+.shes:
+        mov     x14, x5
+        APPEND  shes
+
+.return:
+        ret

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 +1,36 @@
+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/food-chain/food_chain.s

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