Implemented the Intergalactic Transmission exercise

config.json

@@ -569,6 +569,14 @@
         "prerequisites": [],
         "difficulty": 9
       },
+      {
+        "slug": "intergalactic-transmission",
+        "name": "Intergalactic Transmission",
+        "uuid": "1fc2f497-ddd8-4826-bffe-01023efe6bd7",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 9
+      },
       {
         "slug": "zebra-puzzle",
         "name": "Zebra Puzzle",

exercises/practice/intergalactic-transmission/.docs/instructions.md

@@ -0,0 +1,54 @@
+# Instructions
+
+Your job is to help implement
+
+- the transmitter, which calculates the transmission sequence, and
+- the receiver, which decodes it.
+
+A parity bit is simple way of detecting transmission errors.
+The transmitters and receivers can only transmit and receive _exactly_ eight bits at a time (including the parity bit).
+The parity bit is set so that there is an _even_ number of 1 bits in each transmission, and the parity bit is always the first bit from the right.
+So if the receiver receives `11000001`, `01110101` or `01000000` (i.e. a transmission with an odd number of 1 bits), it knows there is an error.
+
+However, messages are rarely this short, and need to be transmitted in a sequence when they are longer.
+
+For example, consider the message `11000000 00000001 11000000 11011110` (or `C0 01 C0 DE` in hex).
+
+Since each transmission contains exactly eight bits, it can only contain seven bits of data and the parity bit.
+A parity bit must then be inserted after every seven bits of data:
+
+```text
+11000000 00000001 11000000 11011110
+      ↑       ↑       ↑       ↑          (7th bits)
+```
+
+The transmission sequence for this message looks like this:
+
+```text
+1100000_ 0000000_ 0111000_ 0001101_ 1110
+       ↑        ↑        ↑        ↑      (parity bits)
+```
+
+The data in the first transmission in the sequence (`1100000`) has two 1 bits (an even number), so the parity bit is 0.
+The first transmission becomes `11000000` (or `C0` in hex).
+
+The data in the next transmission (`0000000`) has zero 1 bits (an even number again), so the parity bit is 0 again.
+The second transmission thus becomes `00000000` (or `00` in hex).
+
+The data for the next two transmissions (`0111000` and `0001101`) have three 1 bits.
+Their parity bits are set to 1 so that they have an even number of 1 bits in the transmission.
+They are transmitted as `01110001` and `00011011` (or `71` and `1B` in hex).
+
+The last transmission (`1110`) has only four bits of data.
+Since exactly eight bits are transmitted at a time and the parity bit is the rightmost bit, three 0 bits and then the parity bit are added to make up eight bits.
+It now looks like this (where `_` is the parity bit):
+
+```text
+1110 000_
+     ↑↑↑   (added 0 bits)
+```
+
+There is an odd number of 1 bits again, so the parity bit is 1.
+The last transmission in the sequence becomes `11100001` (or `E1` in hex).
+
+The entire transmission sequence for this message is `11000000 00000000 01110001 00011011 11100001` (or `C0 00 71 1B E1` in hex).

exercises/practice/intergalactic-transmission/.docs/introduction.md

@@ -0,0 +1,23 @@
+# Introduction
+
+Trillions upon trillions of messages zip between Earth and neighboring galaxies every millisecond.
+But transmitting over such long distances is tricky.
+Pesky solar flares, temporal distortions, stray forces, and even the flap of a space butterfly's wing can cause a random bit to change during transmission.
+
+Now imagine the consequences:
+
+- Crashing the Intergalactic Share Market when "buy low" turns to "sell now".
+- Losing contact with the Kepler Whirl system when "save new worm hole" becomes "cave new worm hole".
+- Or plunging the universe into existential horror by replacing a cowboy emoji 🤠 with a clown emoji 🤡.
+
+Detecting corrupted messages isn't just important — it's critical.
+The receiver _must_ know when something has gone wrong before disaster strikes.
+
+But how?
+Scientists and engineers from across the universe have been battling this problem for eons.
+Entire cosmic AI superclusters churn through the data.
+And then, one day, a legend resurfaces — an ancient, powerful method, whispered in debugging forums, muttered by engineers who've seen too much...
+
+The Parity Bit!
+
+A method so simple, so powerful, that it might just save interstellar communication.

exercises/practice/intergalactic-transmission/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "rmonnet"
+  ],
+  "files": {
+    "solution": [
+      "intergalactic_transmission.odin"
+    ],
+    "test": [
+      "intergalactic_transmission_test.odin"
+    ],
+    "example": [
+      ".meta/example.odin"
+    ]
+  },
+  "blurb": "Add parity bits to a message for transmission",
+  "source": "Kah Goh",
+  "source_url": "https://github.com/exercism/problem-specifications/pull/2543"
+}

exercises/practice/intergalactic-transmission/.meta/example.odin

@@ -0,0 +1,160 @@
+package intergalactic_transmission
+
+transmit_sequence :: proc(msg: []u8) -> (seq: []u8) {
+
+	if len(msg) == 0 { return nil }
+
+	buf: comm_buffer
+	for chunk in msg {
+		transmit_chunk(&buf, chunk)
+	}
+	// There may be some remaining bit in the buffer, flush them.
+	if buf.step != 0 {
+		transmit_overflow(&buf)
+	}
+	return buf.data[:]
+}
+
+decode_message :: proc(seq: []u8) -> (msg: []u8, okay: bool) {
+
+	if len(seq) == 0 { return nil, true }
+
+	buf: comm_buffer
+	for chunk in seq {
+		if !has_even_ones(chunk) {
+			// We got a chunk with invalid parity, abort!
+			delete(buf.data)
+			return nil, false
+		}
+		decode_chunk(&buf, chunk)
+	}
+	// Because the original message is a set of 8bit words,
+	// once we got through all of them, what's left in the overflow register
+	// can only be some zeros (the reminder of a last padded chunk) so there is no need
+	// to flush the receive buffer.
+	return buf.data[:], true
+}
+
+comm_buffer :: struct {
+	step:     u8,
+	overflow: u8,
+	data:     [dynamic]u8,
+}
+
+// Since we only use 7 bits out of each 8bit word, we get leftovers that
+// we store in an overflow register. After the 1st word, the leftover is 1 bit,
+// after the 2nd word, the leftover is 2 bits, ..., after each 7th word,
+// we end up with enough data in the overflow register to send an extra 8bit
+// chunk (including parity bit) herefore the need to flush the buffer every 7
+// messages.
+//
+// For the 1st word, we use the leftmost 7 bits to send and keep the
+// 1 rightmost bit in the overflow register.
+// For the 2nd word of the message, we will use the 6 leftmost bits
+// to build the next tr_chunk and add the 1 bit that was in the overflow
+// register to the right of the 6bit block (that bit came first in the
+// transmission). We will then be left with 2 bits to store in the
+// overflow buffer.
+// We repeat the process with, at each step, one less bit of the
+// message word going into the chunk and one more bit going into
+// the overflow register, until we are left with 7 bits in the
+// overflow register, at which point we can emit two chunks
+// and go back to the situation we were for the 1st message
+// (empty overflow register)
+// The tr_chunk_masks and tr_overflow_masks split the current word
+// into the rigthmost part (going into the tr_chunk) to be sent
+// and the leftmost part (going into the overflow register).
+// At each step that split move by 1 bit to the left.
+transmit_chunk :: proc(buf: ^comm_buffer, chunk: u8) {
+
+	// Use the leftmost (7 - seq)th bits of chunk and store in position (7-seq)..1.
+	tr_chunk := (chunk & tr_chunk_masks[buf.step]) >> buf.step
+	// Add seq-th bits of overflow at position 7..(7-seq+1)
+	if buf.step > 0 {
+		tr_chunk |= (buf.overflow << (8 - buf.step))
+	}
+	// Store the remaining rightmost bits in the overflow register.
+	buf.overflow = chunk & tr_overflow_masks[buf.step]
+	package_chunk_for_transmission(buf, tr_chunk)
+	buf.step += 1
+	// If we have 7 bits in the overflow, we should flush it.
+	if buf.step == 7 {
+		transmit_overflow(buf)
+	}
+
+}
+
+// Every seven steps (when the overflow register has 7 bits)
+// and at the end of the message, we need to flush the
+// overflow register and send what's in there.
+transmit_overflow :: proc(buf: ^comm_buffer) {
+
+	last_chunk := buf.overflow << (8 - buf.step)
+	package_chunk_for_transmission(buf, last_chunk)
+	// Reset the sequence since we emptied the overflow register.
+	buf.step = 0
+}
+
+// Add the parity bit and put the chunk in the data buffer for transmission.
+package_chunk_for_transmission :: proc(buf: ^comm_buffer, chunk: u8) {
+
+	tr_chunk := chunk
+	// Compute and set the parity bit.
+	if !has_even_ones(tr_chunk) {
+		tr_chunk |= 1
+	}
+	append(&buf.data, tr_chunk)
+}
+
+// Each chunk we receive has 7bits usable. We need to
+// collect them in sets of 8bits.
+// For the 1st word received, we store the 7 bits in the overflow
+// register (in the 7 leftmost bits).
+// For the 2nd word, we add the 1 leftmost bit to the
+// content of the overflow (to the right of the register),
+// queue the now full overflow register and then reuse it
+// to store the 6 rightmost remaining bits of the 2nd word.
+// For each successive word, we keep doing this but with
+// one more bit going to complete the previous overflow
+// and one less bit going to the new overflow, until there is
+// no more bits to go in the new overflow. At which point
+// we are back to the same situation as for the first word.
+decode_chunk :: proc(buf: ^comm_buffer, chunk: u8) {
+
+	// Remove the parity bit
+	rc_chunk := (chunk & 0xFE) >> 1
+	if buf.step == 0 {
+		// Store the chunk in the top of the overflow register.
+		buf.overflow = rc_chunk << 1
+	} else {
+		// Store the rightmost bits at the bottom of the overflow register.
+		buf.overflow |= ((rc_chunk & rc_chunk_masks[buf.step - 1]) >> (7 - buf.step))
+		// We have a full overflow register, output it.
+		append(&buf.data, buf.overflow)
+		// Store the leftmost remaining bits at the top of the overflow register.
+		buf.overflow = (rc_chunk & rc_overflow_masks[buf.step - 1]) << (buf.step + 1)
+	}
+	buf.step = (buf.step + 1) % 8
+}
+
+// Check if the word has an even number of bits set to 1.
+has_even_ones :: proc(n: u8) -> bool {
+
+	ones := 0
+	num := n
+	for _ in 0 ..= 7 {
+		if num & 1 == 1 {
+			ones += 1
+		}
+		num = num >> 1
+	}
+	return ones & 1 == 0
+}
+
+// Since these masks splits 8 bits into two parts: tr_chunk_masks[i] + tr_overflow_masks[i] = 0xFF
+tr_chunk_masks := [?]u8{0xFE, 0xFC, 0xF8, 0xF0, 0xE0, 0xC0, 0x80}
+tr_overflow_masks := [?]u8{0x01, 0x03, 0x07, 0x0F, 0x1F, 0x3F, 0x7F}
+
+// Since these masks splits 7 bits into two parts: rc_chunk_masks[i] + rc_overflow_masks[i] = 0x7F
+rc_chunk_masks := [?]u8{0x40, 0x60, 0x70, 0x78, 0x7C, 0x7E, 0x7F}
+rc_overflow_masks := [?]u8{0x3F, 0x1F, 0x0F, 0x07, 0x03, 0x01, 0x00}

exercises/practice/intergalactic-transmission/.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.
+
+[f99d4046-b429-4582-9324-f0bcac7ab51c]
+description = "calculate transmit sequences -> empty message"
+
+[ee27ea2d-8999-4f23-9275-8f6879545f86]
+description = "calculate transmit sequences -> 0x00 is transmitted as 0x0000"
+
+[97f27f98-8020-402d-be85-f21ba54a6df0]
+description = "calculate transmit sequences -> 0x02 is transmitted as 0x0300"
+
+[24712fb9-0336-4e2f-835e-d2350f29c420]
+description = "calculate transmit sequences -> 0x06 is transmitted as 0x0600"
+
+[7630b5a9-dba1-4178-b2a0-4a376f7414e0]
+description = "calculate transmit sequences -> 0x05 is transmitted as 0x0581"
+
+[ab4fe80b-ef8e-4a99-b4fb-001937af415d]
+description = "calculate transmit sequences -> 0x29 is transmitted as 0x2881"
+
+[4e200d84-593b-4449-b7c0-4de1b6a0955e]
+description = "calculate transmit sequences -> 0xc001c0de is transmitted as 0xc000711be1"
+
+[fbc537e9-6b21-4f4a-8c2b-9cf9b702a9b7]
+description = "calculate transmit sequences -> six byte message"
+
+[d5b75adf-b5fc-4f77-b4ab-77653e30f07c]
+description = "calculate transmit sequences -> seven byte message"
+
+[6d8b297b-da1d-435e-bcd7-55fbb1400e73]
+description = "calculate transmit sequences -> eight byte message"
+
+[54a0642a-d5aa-490c-be89-8e171a0cab6f]
+description = "calculate transmit sequences -> twenty byte message"
+
+[9a8084dd-3336-474c-90cb-8a852524604d]
+description = "decode received messages -> empty message"
+
+[879af739-0094-4736-9127-bd441b1ddbbf]
+description = "decode received messages -> zero message"
+
+[7a89eeef-96c5-4329-a246-ec181a8e959a]
+description = "decode received messages -> 0x0300 is decoded to 0x02"
+
+[3e515af7-8b62-417f-960c-3454bca7f806]
+description = "decode received messages -> 0x0581 is decoded to 0x05"
+
+[a1b4a3f7-9f05-4b7a-b86e-d7c6fc3f16a9]
+description = "decode received messages -> 0x2881 is decoded to 0x29"
+
+[2e99d617-4c91-4ad5-9217-e4b2447d6e4a]
+description = "decode received messages -> first byte has wrong parity"
+
+[507e212d-3dae-42e8-88b4-2223838ff8d2]
+description = "decode received messages -> second byte has wrong parity"
+
+[b985692e-6338-46c7-8cea-bc38996d4dfd]
+description = "decode received messages -> 0xcf4b00 is decoded to 0xce94"
+
+[7a1f4d48-696d-4679-917c-21b7da3ff3fd]
+description = "decode received messages -> 0xe2566500 is decoded to 0xe2ad90"
+
+[467549dc-a558-443b-80c5-ff3d4eb305d4]
+description = "decode received messages -> six byte message"
+
+[1f3be5fb-093a-4661-9951-c1c4781c71ea]
+description = "decode received messages -> seven byte message"
+
+[6065b8b3-9dcd-45c9-918c-b427cfdb28c1]
+description = "decode received messages -> last byte has wrong parity"
+
+[98af97b7-9cca-4c4c-9de3-f70e227a4cb1]
+description = "decode received messages -> eight byte message"
+
+[aa7d4785-2bb9-43a4-a38a-203325c464fb]
+description = "decode received messages -> twenty byte message"
+
+[4c86e034-b066-42ac-8497-48f9bc1723c1]
+description = "decode received messages -> wrong parity on 16th byte"

exercises/practice/intergalactic-transmission/intergalactic_transmission.odin

@@ -0,0 +1,11 @@
+package intergalactic_transmission
+
+transmit_sequence :: proc(msg: []u8) -> (seq: []u8) {
+	// Implement this procedure.
+	return nil
+}
+
+decode_message :: proc(seq: []u8) -> (msg: []u8, okay: bool) {
+	// Implement this procedure.
+	return nil, false
+}