Add crypto-square exercise

config.json

@@ -234,6 +234,14 @@
         "prerequisites": [],
         "difficulty": 5
       },
+      {
+        "slug": "crypto-square",
+        "name": "Crypto Square",
+        "uuid": "de268eb1-66a8-4094-b19f-25da515fb7ac",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 7
+      },
       {
         "slug": "nth-prime",
         "name": "Nth Prime",

exercises/practice/crypto-square/.docs/hints.md

@@ -0,0 +1,6 @@
+# Hints
+
+## General
+
+- The `$t0-9` registers can be used to temporarily store values
+- The instructions specify which registers are used as input and output

exercises/practice/crypto-square/.docs/instructions.append.md

@@ -0,0 +1,9 @@
+# Instructions append
+
+## Registers
+
+| Register | Usage        | Type    | Description                   |
+| -------- | ------------ | ------- | ----------------------------- |
+| `$a0`    | input        | address | null-terminated input string  |
+| `$a1`    | input/output | address | null-terminated output string |
+| `$t0-9`  | temporary    | any     | used for temporary storage    |

exercises/practice/crypto-square/.docs/instructions.md

@@ -0,0 +1,71 @@
+# Instructions
+
+Implement the classic method for composing secret messages called a square code.
+
+Given an English text, output the encoded version of that text.
+
+First, the input is normalized: the spaces and punctuation are removed from the English text and the message is down-cased.
+
+Then, the normalized characters are broken into rows.
+These rows can be regarded as forming a rectangle when printed with intervening newlines.
+
+For example, the sentence
+
+```text
+"If man was meant to stay on the ground, god would have given us roots."
+```
+
+is normalized to:
+
+```text
+"ifmanwasmeanttostayonthegroundgodwouldhavegivenusroots"
+```
+
+The plaintext should be organized into a rectangle as square as possible.
+The size of the rectangle should be decided by the length of the message.
+
+If `c` is the number of columns and `r` is the number of rows, then for the rectangle `r` x `c` find the smallest possible integer `c` such that:
+
+- `r * c >= length of message`,
+- and `c >= r`,
+- and `c - r <= 1`.
+
+Our normalized text is 54 characters long, dictating a rectangle with `c = 8` and `r = 7`:
+
+```text
+"ifmanwas"
+"meanttos"
+"tayonthe"
+"groundgo"
+"dwouldha"
+"vegivenu"
+"sroots  "
+```
+
+The coded message is obtained by reading down the columns going left to right.
+
+The message above is coded as:
+
+```text
+"imtgdvsfearwermayoogoanouuiontnnlvtwttddesaohghnsseoau"
+```
+
+Output the encoded text in chunks that fill perfect rectangles `(r X c)`, with `c` chunks of `r` length, separated by spaces.
+For phrases that are `n` characters short of the perfect rectangle, pad each of the last `n` chunks with a single trailing space.
+
+```text
+"imtgdvs fearwer mayoogo anouuio ntnnlvt wttddes aohghn  sseoau "
+```
+
+Notice that were we to stack these, we could visually decode the ciphertext back in to the original message:
+
+```text
+"imtgdvs"
+"fearwer"
+"mayoogo"
+"anouuio"
+"ntnnlvt"
+"wttddes"
+"aohghn "
+"sseoau "
+```

exercises/practice/crypto-square/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "impl.mips"
+    ],
+    "test": [
+      "runner.mips"
+    ],
+    "example": [
+      ".meta/example.mips"
+    ]
+  },
+  "blurb": "Implement the classic method for composing secret messages called a square code.",
+  "source": "J Dalbey's Programming Practice problems",
+  "source_url": "https://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html"
+}

exercises/practice/crypto-square/.meta/example.mips

@@ -0,0 +1,96 @@
+# | Register | Usage        | Type    | Description                        |
+# | -------- | ------------ | ------- | ---------------------------------- |
+# | `$a0`    | input        | address | null-terminated input string       |
+# | `$a1`    | input/output | address | null-terminated output string      |
+# | `$t0`    | temporary    | integer | count of alphanumeric characters   |
+# | `$t1`    | temporary    | integer | number of input columns            |
+# | `$t2`    | temporary    | integer | number of input rows, plus 1       |
+# | `$t3`    | temporary    | integer | product, then output row number    |
+# | `$t4`    | temporary    | address | start of input string              |
+# | `$t5`    | temporary    | address | pointer into output                |
+# | `$t6`    | temporary    | byte    | '0'                                |
+# | `$t7`    | temporary    | byte    | '9'                                |
+# | `$t8`    | temporary    | byte    | 'a'                                |
+# | `$t9`    | temporary    | byte    | 'z'                                |
+# | `$v0`    | temporary    | byte    | character in string                |
+# | `$v1`    | temporary    | address | return address                     |
+
+.globl ciphertext
+
+ciphertext:
+        move    $v1, $ra                # save return address
+        move    $t4, $a0                # start of input string
+        li      $t6, '0'
+        li      $t7, '9'
+        li      $t8, 'a'
+        li      $t9, 'z'
+
+        li      $t0, -1
+count_alphanumeric:
+        addi    $t0, $t0, 1             # count of alphanumeric characters
+        jal     get_input               # return next alphanumeric, or null terminator
+        bnez    $v0, count_alphanumeric
+
+        beqz    $t0, return_empty       # output an empty string when count is 0
+        move    $a0, $t4                # start of input string
+
+        move    $t1, $zero
+increment_columns:
+        addi    $t1, $t1, 1             # number of columns
+        mulu    $t3, $t1, $t1
+        blt     $t3, $t0, increment_columns # repeat while columns * column < count
+
+        subi    $t2, $t1, 2
+increment_rows:
+        addi    $t2, $t2, 1             # number of rows
+        mulu    $t3, $t2, $t1
+        blt     $t3, $t0, increment_rows # repeat while rows * column < count
+
+        add     $t3, $t3, $t1
+        subi    $t3, $t3, 1             # output length is (rows + 1) * columns - 1
+
+        addi    $t2, $t2, 1             # rows + 1
+        add     $t5, $a1, $t3
+        sb      $zero, 0($t5)           # write null terminator
+        li      $v0, ' '
+
+write_space:
+        subi    $t5, $t5, 1
+        sb      $v0, 0($t5)
+        bne     $t5, $a1, write_space
+
+next_output_column:
+        move    $t5, $a1
+        addi    $a1, $a1, 1
+
+        move    $t3, $zero
+next_output_row:
+        addi    $t3, $t3, 1             # 1-based output row number
+        jal     get_input
+        sb      $v0, 0($t5)             # output alphanumeric byte
+        subi    $t0, $t0, 1
+        beqz    $t0, return             # return when decremented count is 0
+        add     $t5, $t5, $t2
+        blt     $t3, $t1, next_output_row
+        j       next_output_column
+
+return_empty:
+        sb      $zero, 0($a1)           # write null terminator
+
+return:
+        jr      $v1
+
+check_input:
+        blt     $v0, $t6, get_input     # reject if < '0'
+        ble     $v0, $t7, accept_input  # accept if numeric
+        ori     $v0, 0x20               # convert to lower case
+        blt     $v0, $t8, get_input     # reject if < 'a'
+        ble     $v0, $t9, accept_input  # accept if alphabetic
+
+get_input:
+        lb      $v0, 0($a0)             # read input byte
+        addi    $a0, $a0, 1
+        bnez    $v0, check_input
+
+accept_input:
+        jr      $ra

exercises/practice/crypto-square/.meta/tests.toml

@@ -0,0 +1,34 @@
+# 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.
+
+[407c3837-9aa7-4111-ab63-ec54b58e8e9f]
+description = "empty plaintext results in an empty ciphertext"
+
+[aad04a25-b8bb-4304-888b-581bea8e0040]
+description = "normalization results in empty plaintext"
+
+[64131d65-6fd9-4f58-bdd8-4a2370fb481d]
+description = "Lowercase"
+
+[63a4b0ed-1e3c-41ea-a999-f6f26ba447d6]
+description = "Remove spaces"
+
+[1b5348a1-7893-44c1-8197-42d48d18756c]
+description = "Remove punctuation"
+
+[8574a1d3-4a08-4cec-a7c7-de93a164f41a]
+description = "9 character plaintext results in 3 chunks of 3 characters"
+
+[a65d3fa1-9e09-43f9-bcec-7a672aec3eae]
+description = "8 character plaintext results in 3 chunks, the last one with a trailing space"
+
+[fbcb0c6d-4c39-4a31-83f6-c473baa6af80]
+description = "54 character plaintext results in 7 chunks, the last two with trailing spaces"

exercises/practice/crypto-square/impl.mips

@@ -0,0 +1,10 @@
+# | Register | Usage        | Type    | Description                   |
+# | -------- | ------------ | ------- | ----------------------------- |
+# | `$a0`    | input        | address | null-terminated input string  |
+# | `$a1`    | input/output | address | null-terminated output string |
+# | `$t0-9`  | temporary    | any     | used for temporary storage    |
+
+.globl ciphertext
+
+ciphertext:
+        jr $ra