Add book-store exercise

config.json

@@ -468,6 +468,14 @@
         "prerequisites": [],
         "difficulty": 8
       },
+      {
+        "slug": "book-store",
+        "name": "Book Store",
+        "uuid": "799fcb2c-939a-4e7d-b8df-c815acc545c7",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 8
+      },
       {
         "slug": "knapsack",
         "name": "Knapsack",

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/.gitignore

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

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

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

@@ -0,0 +1,97 @@
+default rel
+
+section .rodata
+price: dq 0, 3000, 2560, 2160, 1520, 800
+
+section .text
+global total
+total:
+    cld
+    sub rsp, 48 ; reserve stack space
+    xor rax, rax
+    mov rcx, 5
+
+.zero:
+    mov [rsp + 8*rcx], rax ; set book tally to 0
+    loop .zero
+
+    mov rcx, rdi
+    jrcxz .sort ; skip read loop if there are no books
+
+.read:
+    lodsw
+    inc qword [rsp + 8*rax] ; increment book tally
+    loop .read
+
+
+.sort:
+    ; Bubble sort
+    xor r8, r8 ; number of swaps during scan
+    mov rcx, 4
+
+.scan:
+    mov r9, qword [rsp + 8*rcx]
+    mov r10, qword [rsp + 8*rcx + 8]
+    cmp r9, r10
+    jbe .next_pair
+
+    mov qword [rsp + 8*rcx], r10
+    mov qword [rsp + 8*rcx + 8], r9
+    inc r8 ; count swap
+
+.next_pair:
+    loop .scan
+
+    test r8, r8
+    jnz .sort ; repeat until a scan has no swaps
+
+.differences:
+    ; Compute group counts
+    mov rdx, qword [rsp + 8] ; groups of 5
+    mov r8, qword [rsp + 16]
+    mov r9, qword [rsp + 24]
+    mov r10, qword [rsp + 32]
+    mov r11, qword [rsp + 40]
+    sub r11, r10
+    sub r10, r9
+    sub r9, r8
+    sub r8, rdx
+    mov qword [rsp + 16], r8 ; groups of 4
+    mov qword [rsp + 24], r9 ; groups of 3
+    mov qword [rsp + 32], r10 ; groups of 2
+    mov qword [rsp + 40], r11 ; groups of 1
+
+
+    ; Two groups of 4 books are cheaper than a group of 5 books and a group of 4 books
+    mov r8, qword [rsp + 8] ; groups of 5 books
+    mov r9, qword [rsp + 16] ; groups of 4 books
+    mov r10, qword [rsp + 24] ; groups of 3 books
+    mov r11, r10
+    cmp r8, r10
+    cmovb r11, r8 ; r11 now has min(groups of 5 books, groups of 3 books)
+    sub r8, r11
+    sub r10, r11
+    shl r11, 1
+    add r9, r11
+    mov qword [rsp + 8], r8
+    mov qword [rsp + 16], r9
+    mov qword [rsp + 24], r10
+
+    xor r10, r10
+    lea r11, [price]
+    mov rcx, 5
+
+.multiply:
+    mov rax, qword [rsp + rcx*8] ; number of groups
+    mov rdx, qword [r11 + rcx*8] ; price of each group
+    mul rdx
+    add r10, rax ; accumulate total price
+    loop .multiply
+
+    mov rax, r10
+    add rsp, 48 ; restore original stack pointer
+    ret
+
+%ifidn __OUTPUT_FORMAT__,elf64
+section .note.GNU-stack noalloc noexec nowrite progbits
+%endif

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 +1,46 @@
+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/book-store/book_store.asm

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