Add book-store exercise (#137)

config.json

@@ -482,6 +482,14 @@
         "prerequisites": [],
         "difficulty": 7
       },
+      {
+        "slug": "book-store",
+        "name": "Book Store",
+        "uuid": "a01d25e1-021c-40ed-983e-fdda79556aaa",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 8
+      },
       {
         "slug": "meetup",
         "name": "Meetup",

exercises/practice/book-store/.docs/instructions.md

@@ -0,0 +1,61 @@
+# Instructions
+
+To try and encourage more sales of different books from a popular 5 book series, a bookshop has decided to offer discounts on multiple book purchases.
+
+One copy of any of the five books costs $8.
+
+If, however, you buy two different books, you get a 5% discount on those two books.
+
+If you buy 3 different books, you get a 10% discount.
+
+If you buy 4 different books, you get a 20% discount.
+
+If you buy all 5, you get a 25% discount.
+
+Note that if you buy four books, of which 3 are different titles, you get a 10% discount on the 3 that form part of a set, but the fourth book still costs $8.
+
+Your mission is to write code to calculate the price of any conceivable shopping basket (containing only books of the same series), giving as big a discount as possible.
+
+For example, how much does this basket of books cost?
+
+- 2 copies of the first book
+- 2 copies of the second book
+- 2 copies of the third book
+- 1 copy of the fourth book
+- 1 copy of the fifth book
+
+One way of grouping these 8 books is:
+
+- 1 group of 5 (1st, 2nd,3rd, 4th, 5th)
+- 1 group of 3 (1st, 2nd, 3rd)
+
+This would give a total of:
+
+- 5 books at a 25% discount
+- 3 books at a 10% discount
+
+Resulting in:
+
+- 5 × (100% - 25%) × $8 = 5 × $6.00 = $30.00, plus
+- 3 × (100% - 10%) × $8 = 3 × $7.20 = $21.60
+
+Which equals $51.60.
+
+However, a different way to group these 8 books is:
+
+- 1 group of 4 books (1st, 2nd, 3rd, 4th)
+- 1 group of 4 books (1st, 2nd, 3rd, 5th)
+
+This would give a total of:
+
+- 4 books at a 20% discount
+- 4 books at a 20% discount
+
+Resulting in:
+
+- 4 × (100% - 20%) × $8 = 4 × $6.40 = $25.60, plus
+- 4 × (100% - 20%) × $8 = 4 × $6.40 = $25.60
+
+Which equals $51.20.
+
+And $51.20 is the price with the biggest discount.

exercises/practice/book-store/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "book_store.s"
+    ],
+    "test": [
+      "book_store_test.c"
+    ],
+    "example": [
+      ".meta/example.s"
+    ]
+  },
+  "blurb": "To try and encourage more sales of different books from a popular 5 book series, a bookshop has decided to offer discounts of multiple-book purchases.",
+  "source": "Inspired by the harry potter kata from Cyber-Dojo.",
+  "source_url": "https://cyber-dojo.org"
+}

exercises/practice/book-store/.meta/example.s

@@ -0,0 +1,122 @@
+.text
+.globl total
+
+/* void count(size_t basket_count, const uint16_t *basket, uint16_t *tally); */
+count:
+        lsl     x0, x0, #1              /* number of bytes occupied by array */
+        cbz     x0, .return
+
+.loop:
+        sub     x0, x0, #2
+        ldrh    w10, [x1, x0]           /* book */
+        lsl     w10, w10, #1
+        ldrh    w11, [x2, x10]
+        add     w11, w11, #1            /* increment tally */
+        strh    w11, [x2, x10]
+        cbnz    x0, .loop
+
+.return:
+        ret
+
+/* extern void sort(uint16_t *tally) */
+sort:
+        mov     w9, #4                  /* offsets 4..10 for books 2..5 */
+
+.outer:
+        ldrh    w12, [x0, x9]
+        mov     w10, w9                 /* offset for inner loop of insertion sort */
+
+.inner:
+        sub     w11, w10, #2
+        cbz     w11, .exit
+
+        ldrh    w13, [x0, x11]
+        cmp     w13, w12
+        bge     .exit
+
+        strh    w13, [x0, x10]
+        mov     w10, w11
+        b       .inner
+
+.exit:
+        strh    w12, [x0, x10]
+
+        add     w9, w9, #2
+        cmp     w9, #10
+        ble     .outer
+
+        ret
+
+/* void difference(uint16_t *tally); */
+difference:
+        ldrh    w10, [x0, #10]
+        ldrh    w11, [x0, #8]
+        sub     w12, w11, w10
+        strh    w12, [x0, #8]           /* tally[4] - tally[5] */
+
+        ldrh    w10, [x0, #6]
+        sub     w12, w10, w11
+        strh    w12, [x0, #6]           /* tally[3] - tally[4] */
+
+        ldrh    w11, [x0, #4]
+        sub     w12, w11, w10
+        strh    w12, [x0, #4]           /* tally[2] - tally[3] */
+
+        ldrh    w10, [x0, #2]
+        sub     w12, w10, w11
+        strh    w12, [x0, #2]           /* tally[1] - tally[2] */
+        ret
+
+/* void adjust(uint16_t *tally); */
+adjust:
+        ldrh    w11, [x0, #6]
+        ldrh    w12, [x0, #8]
+        ldrh    w13, [x0, #10]
+        cmp     w11, w13
+        csel    w14, w11, w13, lt       /* smallest of tallies for 3 and 5 books */
+
+        sub     w11, w11, w14
+        sub     w13, w13, w14           /* replace each pair of groups of 3 and 5 books */
+        lsl     w14, w14, #1            /* with pairs of groups of 4 books */
+        add     w12, w12, w14
+        strh    w11, [x0, #6]
+        strh    w12, [x0, #8]
+        strh    w13, [x0, #10]
+        ret
+
+/* uint32_t score(uint16_t *tally); */
+score:
+        ldrh    w11, [x0, #2]
+        mov     w10, #800               /* price of 1 book */
+        mul     w12, w10, w11
+
+        ldrh    w11, [x0, #4]
+        mov     w10, #1520              /* price of 2 books */
+        madd    w12, w10, w11, w12
+
+        ldrh    w11, [x0, #6]
+        mov     w10, #2160              /* price of 3 books */
+        madd    w12, w10, w11, w12
+
+        ldrh    w11, [x0, #8]
+        mov     w10, #2560              /* price of 4 books */
+        madd    w12, w10, w11, w12
+
+        ldrh    w11, [x0, #10]
+        mov     w10, #3000              /* price of 5 books */
+        madd    w0, w10, w11, w12
+        ret
+
+/* extern uint32_t total(size_t basket_count, const uint16_t *basket); */
+total:
+        mov     x15, lr                 /* save return address */
+        stp     xzr, xzr, [sp, #-16]!
+        mov     x2, sp
+        bl      count
+        mov     x0, sp
+        bl      sort
+        bl      difference
+        bl      adjust
+        bl      score
+        add     sp, sp, #16
+        ret     x15

exercises/practice/book-store/.meta/tests.toml

@@ -0,0 +1,64 @@
+# 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.
+
+[17146bd5-2e80-4557-ab4c-05632b6b0d01]
+description = "Only a single book"
+
+[cc2de9ac-ff2a-4efd-b7c7-bfe0f43271ce]
+description = "Two of the same book"
+
+[5a86eac0-45d2-46aa-bbf0-266b94393a1a]
+description = "Empty basket"
+
+[158bd19a-3db4-4468-ae85-e0638a688990]
+description = "Two different books"
+
+[f3833f6b-9332-4a1f-ad98-6c3f8e30e163]
+description = "Three different books"
+
+[1951a1db-2fb6-4cd1-a69a-f691b6dd30a2]
+description = "Four different books"
+
+[d70f6682-3019-4c3f-aede-83c6a8c647a3]
+description = "Five different books"
+
+[78cacb57-911a-45f1-be52-2a5bd428c634]
+description = "Two groups of four is cheaper than group of five plus group of three"
+
+[f808b5a4-e01f-4c0d-881f-f7b90d9739da]
+description = "Two groups of four is cheaper than groups of five and three"
+
+[fe96401c-5268-4be2-9d9e-19b76478007c]
+description = "Group of four plus group of two is cheaper than two groups of three"
+
+[68ea9b78-10ad-420e-a766-836a501d3633]
+description = "Two each of first four books and one copy each of rest"
+
+[c0a779d5-a40c-47ae-9828-a340e936b866]
+description = "Two copies of each book"
+
+[18fd86fe-08f1-4b68-969b-392b8af20513]
+description = "Three copies of first book and two each of remaining"
+
+[0b19a24d-e4cf-4ec8-9db2-8899a41af0da]
+description = "Three each of first two books and two each of remaining books"
+
+[bb376344-4fb2-49ab-ab85-e38d8354a58d]
+description = "Four groups of four are cheaper than two groups each of five and three"
+
+[5260ddde-2703-4915-b45a-e54dbbac4303]
+description = "Check that groups of four are created properly even when there are more groups of three than groups of five"
+
+[b0478278-c551-4747-b0fc-7e0be3158b1f]
+description = "One group of one and four is cheaper than one group of two and three"
+
+[cf868453-6484-4ae1-9dfc-f8ee85bbde01]
+description = "One group of one and two plus three groups of four is cheaper than one group of each size"

exercises/practice/book-store/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/book-store/book_store.s

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