Add pascals-triangle exercise

config.json

@@ -242,6 +242,14 @@
         "prerequisites": [],
         "difficulty": 6
       },
+      {
+        "slug": "pascals-triangle",
+        "name": "Pascal's Triangle",
+        "uuid": "46295ef5-0bcb-423f-8eaf-31e69ef51055",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6
+      },
       {
         "slug": "zebra-puzzle",
         "name": "Zebra Puzzle",

exercises/practice/pascals-triangle/.docs/instructions.md

@@ -0,0 +1,35 @@
+# Instructions
+
+Your task is to output the first N rows of Pascal's triangle.
+
+[Pascal's triangle][wikipedia] is a triangular array of positive integers.
+
+In Pascal's triangle, the number of values in a row is equal to its row number (which starts at one).
+Therefore, the first row has one value, the second row has two values, and so on.
+
+The first (topmost) row has a single value: `1`.
+Subsequent rows' values are computed by adding the numbers directly to the right and left of the current position in the previous row.
+
+If the previous row does _not_ have a value to the left or right of the current position (which only happens for the leftmost and rightmost positions), treat that position's value as zero (effectively "ignoring" it in the summation).
+
+## Example
+
+Let's look at the first 5 rows of Pascal's Triangle:
+
+```text
+    1
+   1 1
+  1 2 1
+ 1 3 3 1
+1 4 6 4 1
+```
+
+The topmost row has one value, which is `1`.
+
+The leftmost and rightmost values have only one preceding position to consider, which is the position to its right respectively to its left.
+With the topmost value being `1`, it follows from this that all the leftmost and rightmost values are also `1`.
+
+The other values all have two positions to consider.
+For example, the fifth row's (`1 4 6 4 1`) middle value is `6`, as the values to its left and right in the preceding row are `3` and `3`:
+
+[wikipedia]: https://en.wikipedia.org/wiki/Pascal%27s_triangle

exercises/practice/pascals-triangle/.docs/introduction.md

@@ -0,0 +1,22 @@
+# Introduction
+
+With the weather being great, you're not looking forward to spending an hour in a classroom.
+Annoyed, you enter the class room, where you notice a strangely satisfying triangle shape on the blackboard.
+Whilst waiting for your math teacher to arrive, you can't help but notice some patterns in the triangle: the outer values are all ones, each subsequent row has one more value than its previous row and the triangle is symmetrical.
+Weird!
+
+Not long after you sit down, your teacher enters the room and explains that this triangle is the famous [Pascal's triangle][wikipedia].
+
+Over the next hour, your teacher reveals some amazing things hidden in this triangle:
+
+- It can be used to compute how many ways you can pick K elements from N values.
+- It contains the Fibonacci sequence.
+- If you color odd and even numbers differently, you get a beautiful pattern called the [Sierpiński triangle][wikipedia-sierpinski-triangle].
+
+The teacher implores you and your classmates to lookup other uses, and assures you that there are lots more!
+At that moment, the school bell rings.
+You realize that for the past hour, you were completely absorbed in learning about Pascal's triangle.
+You quickly grab your laptop from your bag and go outside, ready to enjoy both the sunshine _and_ the wonders of Pascal's triangle.
+
+[wikipedia]: https://en.wikipedia.org/wiki/Pascal%27s_triangle
+[wikipedia-sierpinski-triangle]: https://en.wikipedia.org/wiki/Sierpi%C5%84ski_triangle

exercises/practice/pascals-triangle/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "pascals_triangle.s"
+    ],
+    "test": [
+      "pascals_triangle_test.c"
+    ],
+    "example": [
+      ".meta/example.s"
+    ]
+  },
+  "blurb": "Compute Pascal's triangle up to a given number of rows.",
+  "source": "Pascal's Triangle at Wolfram Math World",
+  "source_url": "https://www.wolframalpha.com/input/?i=Pascal%27s+triangle"
+}

exercises/practice/pascals-triangle/.meta/example.s

@@ -0,0 +1,54 @@
+.text
+.globl rows
+
+/* extern size_t rows(uint64_t* dest, size_t count); */
+rows:
+
+/*
+| `x0`    | input/output | address | start of array                   |
+| `x0`    | output       | integer | number of output elements        |
+| `x1`    | input        | integer | count of triangle rows           |
+| `x1`    | temporary    | integer | number of bytes in x1 elements   |
+| `x2`    | temporary    | address | output pointer                   |
+| `x3`    | temporary    | integer | sum two values from previous row |
+| `x4`    | temporary    | integer | row length, in bytes             |
+| `x5`    | temporary    | address | pointer into previous row        |
+| `x6`    | temporary    | address | initial 1 of current row         |
+| `x7`    | temporary    | address | final 1 of current row           |
+| `x8`    | temporary    | integer | left value from previous row     |
+| `x9`    | temporary    | integer | right value from previous row    |
+*/
+
+        mov     x2, x0                  /* output pointer */
+        cbz     x1, .done               /* stop immediately if 0 rows */
+
+        lsl     x1, x1, #3              /* number of bytes in count elements */
+        mov     x4, xzr                 /* current row length, in bytes */
+        mov     x9, #1                  /* right value from previous row */
+
+.next_row:
+        mov     x6, x2                  /* address of initial 1 of current row */
+        add     x7, x2, x4              /* address of final 1 of current row */
+        add     x4, x4, #8              /* row length, in bytes */
+        mov     x8, xzr                 /* left value from previous row */
+        cmp     x2, x7
+        beq     .last_column
+
+.next_column:
+        ldr     x9, [x5], #8            /* read from previous row, post-increment */
+        add     x3, x8, x9              /* sum two values from previous row */
+        mov     x8, x9
+        str     x3, [x2], #8            /* write output, post-increment */
+        cmp     x2, x7
+        bne     .next_column
+
+.last_column:
+        str     x9, [x2], #8            /* write output, post-increment */
+        mov     x5, x6                  /* start of most recent row */
+        cmp     x4, x1
+        bne     .next_row               /* repeat until we have final row length */
+
+.done:
+        sub     x0, x2, x0              /* subtract start of output */
+        lsr     x0, x0, #3              /* convert to number of elements */
+        ret

exercises/practice/pascals-triangle/.meta/tests.toml

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+# 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.
+
+[9920ce55-9629-46d5-85d6-4201f4a4234d]
+description = "zero rows"
+
+[70d643ce-a46d-4e93-af58-12d88dd01f21]
+description = "single row"
+
+[a6e5a2a2-fc9a-4b47-9f4f-ed9ad9fbe4bd]
+description = "two rows"
+
+[97206a99-79ba-4b04-b1c5-3c0fa1e16925]
+description = "three rows"
+
+[565a0431-c797-417c-a2c8-2935e01ce306]
+description = "four rows"
+
+[06f9ea50-9f51-4eb2-b9a9-c00975686c27]
+description = "five rows"
+
+[c3912965-ddb4-46a9-848e-3363e6b00b13]
+description = "six rows"
+
+[6cb26c66-7b57-4161-962c-81ec8c99f16b]
+description = "ten rows"

exercises/practice/pascals-triangle/Makefile

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+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/pascals-triangle/pascals_triangle.s

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