add variable-length-quantity exercise

config.json

@@ -910,6 +910,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 5
+      },
+      {
+        "slug": "variable-length-quantity",
+        "name": "Variable Length Quantity",
+        "uuid": "5073fd82-3025-4370-ae93-37b661c17483",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6
       }
     ]
   },
@@ -956,4 +964,4 @@
     "typing/strong",
     "used_for/scripts"
   ]
-}
+}

exercises/practice/variable-length-quantity/.docs/instructions.md

@@ -0,0 +1,34 @@
+# Instructions
+
+Implement variable length quantity encoding and decoding.
+
+The goal of this exercise is to implement [VLQ][vlq] encoding/decoding.
+
+In short, the goal of this encoding is to encode integer values in a way that would save bytes.
+Only the first 7 bits of each byte are significant (right-justified; sort of like an ASCII byte).
+So, if you have a 32-bit value, you have to unpack it into a series of 7-bit bytes.
+Of course, you will have a variable number of bytes depending upon your integer.
+To indicate which is the last byte of the series, you leave bit #7 clear.
+In all of the preceding bytes, you set bit #7.
+
+So, if an integer is between `0-127`, it can be represented as one byte.
+Although VLQ can deal with numbers of arbitrary sizes, for this exercise we will restrict ourselves to only numbers that fit in a 32-bit unsigned integer.
+Here are examples of integers as 32-bit values, and the variable length quantities that they translate to:
+
+```text
+ NUMBER        VARIABLE QUANTITY
+00000000              00
+00000040              40
+0000007F              7F
+00000080             81 00
+00002000             C0 00
+00003FFF             FF 7F
+00004000           81 80 00
+00100000           C0 80 00
+001FFFFF           FF FF 7F
+00200000          81 80 80 00
+08000000          C0 80 80 00
+0FFFFFFF          FF FF FF 7F
+```
+
+[vlq]: https://en.wikipedia.org/wiki/Variable-length_quantity

exercises/practice/variable-length-quantity/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "kmarker1101"
+  ],
+  "files": {
+    "solution": [
+      "variable-length-quantity.el"
+    ],
+    "test": [
+      "variable-length-quantity-test.el"
+    ],
+    "example": [
+      ".meta/example.el"
+    ]
+  },
+  "blurb": "Implement variable length quantity encoding and decoding.",
+  "source": "A poor Splice developer having to implement MIDI encoding/decoding.",
+  "source_url": "https://splice.com"
+}

exercises/practice/variable-length-quantity/.meta/example.el

@@ -0,0 +1,43 @@
+;;; variable-length-quantity.el --- Variable Length Quantity (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+
+(define-error 'incomplete "incomplete sequence")
+
+
+(defun encode (numbers)
+  "Encode a list of numbers into VLQ format."
+  (let ((encode-single (lambda (number)
+                         (let ((byte-string (list (logand number 127)))) ; Initialize with the least significant byte
+                           (setq number (lsh number -7)) ; Shift right before the loop
+                           (while (> number 0)
+                             (push (logior (logand number 127) 128) byte-string)
+                             (setq number (lsh number -7)))
+                           byte-string))))
+    (apply #'append (mapcar encode-single numbers))))
+
+
+(defun decode (byte-string)
+  "Decode a byte string from VLQ format into numbers."
+  (let ((values '())
+        (number 0)
+        (incomplete t))
+    (dolist (byte byte-string)
+      (setq number (lsh number 7))
+      (setq number (logior number (logand byte 127)))
+      (if (= (logand byte 128) 0)
+          (progn
+            (setq values (cons number values))
+            (setq number 0)
+            (setq incomplete nil))
+        (setq incomplete t)))
+    (if incomplete
+        (signal 'incomplete 'nil)
+      (reverse values))))
+
+
+(provide 'variable-length-quantity)
+;;; variable-length-quantity.el ends here

exercises/practice/variable-length-quantity/.meta/tests.toml

@@ -0,0 +1,88 @@
+# 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.
+
+[35c9db2e-f781-4c52-b73b-8e76427defd0]
+description = "Encode a series of integers, producing a series of bytes. -> zero"
+
+[be44d299-a151-4604-a10e-d4b867f41540]
+description = "Encode a series of integers, producing a series of bytes. -> arbitrary single byte"
+
+[ea399615-d274-4af6-bbef-a1c23c9e1346]
+description = "Encode a series of integers, producing a series of bytes. -> largest single byte"
+
+[77b07086-bd3f-4882-8476-8dcafee79b1c]
+description = "Encode a series of integers, producing a series of bytes. -> smallest double byte"
+
+[63955a49-2690-4e22-a556-0040648d6b2d]
+description = "Encode a series of integers, producing a series of bytes. -> arbitrary double byte"
+
+[29da7031-0067-43d3-83a7-4f14b29ed97a]
+description = "Encode a series of integers, producing a series of bytes. -> largest double byte"
+
+[3345d2e3-79a9-4999-869e-d4856e3a8e01]
+description = "Encode a series of integers, producing a series of bytes. -> smallest triple byte"
+
+[5df0bc2d-2a57-4300-a653-a75ee4bd0bee]
+description = "Encode a series of integers, producing a series of bytes. -> arbitrary triple byte"
+
+[f51d8539-312d-4db1-945c-250222c6aa22]
+description = "Encode a series of integers, producing a series of bytes. -> largest triple byte"
+
+[da78228b-544f-47b7-8bfe-d16b35bbe570]
+description = "Encode a series of integers, producing a series of bytes. -> smallest quadruple byte"
+
+[11ed3469-a933-46f1-996f-2231e05d7bb6]
+description = "Encode a series of integers, producing a series of bytes. -> arbitrary quadruple byte"
+
+[d5f3f3c3-e0f1-4e7f-aad0-18a44f223d1c]
+description = "Encode a series of integers, producing a series of bytes. -> largest quadruple byte"
+
+[91a18b33-24e7-4bfb-bbca-eca78ff4fc47]
+description = "Encode a series of integers, producing a series of bytes. -> smallest quintuple byte"
+
+[5f34ff12-2952-4669-95fe-2d11b693d331]
+description = "Encode a series of integers, producing a series of bytes. -> arbitrary quintuple byte"
+
+[7489694b-88c3-4078-9864-6fe802411009]
+description = "Encode a series of integers, producing a series of bytes. -> maximum 32-bit integer input"
+
+[f9b91821-cada-4a73-9421-3c81d6ff3661]
+description = "Encode a series of integers, producing a series of bytes. -> two single-byte values"
+
+[68694449-25d2-4974-ba75-fa7bb36db212]
+description = "Encode a series of integers, producing a series of bytes. -> two multi-byte values"
+
+[51a06b5c-de1b-4487-9a50-9db1b8930d85]
+description = "Encode a series of integers, producing a series of bytes. -> many multi-byte values"
+
+[baa73993-4514-4915-bac0-f7f585e0e59a]
+description = "Decode a series of bytes, producing a series of integers. -> one byte"
+
+[72e94369-29f9-46f2-8c95-6c5b7a595aee]
+description = "Decode a series of bytes, producing a series of integers. -> two bytes"
+
+[df5a44c4-56f7-464e-a997-1db5f63ce691]
+description = "Decode a series of bytes, producing a series of integers. -> three bytes"
+
+[1bb58684-f2dc-450a-8406-1f3452aa1947]
+description = "Decode a series of bytes, producing a series of integers. -> four bytes"
+
+[cecd5233-49f1-4dd1-a41a-9840a40f09cd]
+description = "Decode a series of bytes, producing a series of integers. -> maximum 32-bit integer"
+
+[e7d74ba3-8b8e-4bcb-858d-d08302e15695]
+description = "Decode a series of bytes, producing a series of integers. -> incomplete sequence causes error"
+
+[aa378291-9043-4724-bc53-aca1b4a3fcb6]
+description = "Decode a series of bytes, producing a series of integers. -> incomplete sequence causes error, even if value is zero"
+
+[a91e6f5a-c64a-48e3-8a75-ce1a81e0ebee]
+description = "Decode a series of bytes, producing a series of integers. -> multiple values"

exercises/practice/variable-length-quantity/variable-length-quantity-test.el

@@ -0,0 +1,118 @@
+;;; variable-length-quantity-test.el --- Variable Length Quantity (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+
+(load-file "variable-length-quantity.el")
+(declare-function encode "variable-length-quantity.el" (integers))
+(declare-function decode "variable-length-quantity.el" (integers))
+
+
+(ert-deftest zero ()
+  (should (equal (encode '(0)) '(0))))
+
+
+(ert-deftest arbitrary-single-byte ()
+  (should (equal (encode '(64)) '(64))))
+
+
+(ert-deftest largest-single-byte ()
+  (should (equal (encode '(127)) '(127))))
+
+
+(ert-deftest smallest-double-byte ()
+  (should (equal (encode '(128)) '(129 0))))
+
+
+(ert-deftest arbitrary-double-byte ()
+  (should (equal (encode '(8192)) '(192 0))))
+
+
+(ert-deftest largest-double-byte ()
+  (should (equal (encode '(16383)) '(255 127))))
+
+
+(ert-deftest smallest-triple-byte ()
+  (should (equal (encode '(16384)) '(129 128 0))))
+
+
+(ert-deftest arbitrary-triple-byte ()
+  (should (equal (encode '(1048576)) '(192 128 0))))
+
+
+(ert-deftest largest-triple-byte ()
+  (should (equal (encode '(2097151)) '(255 255 127))))
+
+
+(ert-deftest smallest-quadruple-byte ()
+  (should (equal (encode '(2097152)) '(129 128 128 0))))
+
+
+(ert-deftest arbitrary-quadruple-byte ()
+  (should (equal (encode '(134217728)) '(192 128 128 0))))
+
+
+(ert-deftest largest-quadruple-byte ()
+  (should (equal (encode '(268435455)) '(255 255 255 127))))
+
+
+(ert-deftest smallest-quintuple-byte ()
+  (should (equal (encode '(268435456)) '(129 128 128 128 0))))
+
+
+(ert-deftest arbitrary-quintuple-byte ()
+  (should (equal (encode '(4278190080)) '(143 248 128 128 0))))
+
+
+(ert-deftest maximum-32-bit-integer-input ()
+  (should (equal (encode '(4294967295)) '(143 255 255 255 127))))
+
+
+(ert-deftest two-single-byte-values ()
+  (should (equal (encode '(64 127)) '(64 127))))
+
+
+(ert-deftest two-multi-byte-values ()
+  (should (equal (encode '(16384 1193046)) '(129 128 0 200 232 86))))
+
+
+(ert-deftest many-multi-byte-values ()
+  (should (equal (encode '(8192 1193046 268435455 0 16383 16384)) '(192 0 200 232 86 255 255 255 127 0 255 127 129 128 0))))
+
+
+(ert-deftest one-byte ()
+  (should (equal (decode '(127)) '(127))))
+
+
+(ert-deftest two-bytes ()
+  (should (equal (decode '(192 0)) '(8192))))
+
+
+(ert-deftest three-bytes ()
+  (should (equal (decode '(255 255 127)) '(2097151))))
+
+
+(ert-deftest four-bytes ()
+  (should (equal (decode '(129 128 128 0)) '(2097152))))
+
+
+(ert-deftest maximum-32-bit-integer ()
+  (should (equal (decode '(143 255 255 255 127)) '(4294967295))))
+
+
+(ert-deftest incomplete-sequence-causes-error ()
+  (should-error (decode '(255)) :type 'incomplete))
+
+
+(ert-deftest incomplete-sequence-causes-error-even-if-value-is-zero ()
+  (should-error (decode '(128)) :type 'incomplete))
+
+
+(ert-deftest multiple-values ()
+  (should (equal (decode '(192 0 200 232 86 255 255 255 127 0 255 127 129 128 0)) '(8192 1193046 268435455 0 16383 16384))))
+
+
+(provide 'variable-length-quantity-test)
+;;; variable-length-quantity-test.el ends here

exercises/practice/variable-length-quantity/variable-length-quantity.el

@@ -0,0 +1,22 @@
+;;; variable-length-quantity.el --- Variable Length Quantity (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+
+(define-error 'incomplete
+              (error "Delete this S-Expression and write your own implementation"))
+
+
+(defun encode (integers)
+  (error "Delete this S-Expression and write your own implementation"))
+
+
+(defun decode (integers)
+  (error "Delete this S-Expression and write your own implementation"))
+
+
+(provide 'variable-length-quantity)
+;;; variable-length-quantity.el ends here
+