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Add intergalactic-transmission (#277)
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‎config.json

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"prerequisites": [],
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"difficulty": 6
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},
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{
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"slug": "intergalactic-transmission",
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"name": "Intergalactic Transmission",
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"uuid": "c24ff280-84fe-4d70-a0ef-94748da57d40",
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"practices": [],
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"prerequisites": [],
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"difficulty": 6
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},
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{
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"slug": "luhn",
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"name": "Luhn",

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

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

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

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

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{
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"authors": [
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"keiravillekode"
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],
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"files": {
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"solution": [
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"intergalactic_transmission.asm"
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],
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"test": [
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"intergalactic_transmission_test.c"
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],
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"example": [
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".meta/example.asm"
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]
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},
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"blurb": "Add parity bits to a message for transmission",
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"source": "Kah Goh",
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"source_url": "https://github.com/exercism/problem-specifications/pull/2543"
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}

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

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WRONG_PARITY equ -1
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section .text
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global transmit_sequence, decode_message
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; extern int transmit_sequence(uint8_t *buffer, const uint8_t *message, int message_length);
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transmit_sequence:
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mov r8, rdi ; buffer
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test rdx, rdx
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jz .transmit_success
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cld
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add rdx, rsi ; end of message
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xor cl, cl ; number of pending bits
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xor r10, r10 ; value of pending bits
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.transmit_read:
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shl r10, 8
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lodsb ; read
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or r10b, al
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add cl, 8
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.transmit_encode:
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sub cl, 7
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mov rax, r10
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shr rax, cl
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shl al, 1
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test al, al
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jp .transmit_write
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or al, 1
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.transmit_write:
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stosb ; write
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cmp cl, 7
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je .transmit_encode
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cmp rsi, rdx
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jne .transmit_read ; more to read?
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test cl, cl
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jz .transmit_success ; no more bits to transmit?
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neg cl
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add cl, 7 ; 7 minus number of pending bits
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shl r10, cl
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mov cl, 7
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jmp .transmit_encode
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.transmit_success:
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mov rax, rdi
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sub rax, r8
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ret
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; extern int decode_message(uint8_t *buffer, const uint8_t *message, int message_length);
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decode_message:
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mov r8, rdi ; buffer
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xor cl, cl ; number of pending bits
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xor r10, r10 ; value of pending bits
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cld
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add rdx, rsi ; end of message
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jmp .decode_check_remaining
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.decode_without_write:
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mov cl, 7
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.decode_read:
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lodsb ; read byte
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test al, al
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jnp .decode_failure
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shr al, 1 ; discard parity bit
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shl r10, 7
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or r10b, al
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test cl, cl
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jz .decode_without_write
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dec cl ; we read 7 bits but write 8
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mov rax, r10
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shr rax, cl
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stosb ; write
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.decode_check_remaining:
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cmp rsi, rdx
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jne .decode_read
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.decode_success:
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mov rax, rdi
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sub rax, r8
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ret
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.decode_failure:
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mov rax, WRONG_PARITY
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ret
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%ifidn __OUTPUT_FORMAT__,elf64
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section .note.GNU-stack noalloc noexec nowrite progbits
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%endif

‎exercises/practice/intergalactic-transmission/.meta/tests.toml

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# This is an auto-generated file.
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#
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# Regenerating this file via `configlet sync` will:
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# - Recreate every `description` key/value pair
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# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
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# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
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# - Preserve any other key/value pair
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#
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# As user-added comments (using the # character) will be removed when this file
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# is regenerated, comments can be added via a `comment` key.
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[f99d4046-b429-4582-9324-f0bcac7ab51c]
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description = "calculate transmit sequences -> empty message"
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[ee27ea2d-8999-4f23-9275-8f6879545f86]
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description = "calculate transmit sequences -> 0x00 is transmitted as 0x0000"
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[97f27f98-8020-402d-be85-f21ba54a6df0]
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description = "calculate transmit sequences -> 0x02 is transmitted as 0x0300"
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[24712fb9-0336-4e2f-835e-d2350f29c420]
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description = "calculate transmit sequences -> 0x06 is transmitted as 0x0600"
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[7630b5a9-dba1-4178-b2a0-4a376f7414e0]
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description = "calculate transmit sequences -> 0x05 is transmitted as 0x0581"
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[ab4fe80b-ef8e-4a99-b4fb-001937af415d]
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description = "calculate transmit sequences -> 0x29 is transmitted as 0x2881"
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[4e200d84-593b-4449-b7c0-4de1b6a0955e]
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description = "calculate transmit sequences -> 0xc001c0de is transmitted as 0xc000711be1"
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[fbc537e9-6b21-4f4a-8c2b-9cf9b702a9b7]
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description = "calculate transmit sequences -> six byte message"
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[d5b75adf-b5fc-4f77-b4ab-77653e30f07c]
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description = "calculate transmit sequences -> seven byte message"
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[6d8b297b-da1d-435e-bcd7-55fbb1400e73]
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description = "calculate transmit sequences -> eight byte message"
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[54a0642a-d5aa-490c-be89-8e171a0cab6f]
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description = "calculate transmit sequences -> twenty byte message"
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[9a8084dd-3336-474c-90cb-8a852524604d]
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description = "decode received messages -> empty message"
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[879af739-0094-4736-9127-bd441b1ddbbf]
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description = "decode received messages -> zero message"
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[7a89eeef-96c5-4329-a246-ec181a8e959a]
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description = "decode received messages -> 0x0300 is decoded to 0x02"
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[3e515af7-8b62-417f-960c-3454bca7f806]
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description = "decode received messages -> 0x0581 is decoded to 0x05"
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[a1b4a3f7-9f05-4b7a-b86e-d7c6fc3f16a9]
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description = "decode received messages -> 0x2881 is decoded to 0x29"
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[2e99d617-4c91-4ad5-9217-e4b2447d6e4a]
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description = "decode received messages -> first byte has wrong parity"
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[507e212d-3dae-42e8-88b4-2223838ff8d2]
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description = "decode received messages -> second byte has wrong parity"
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[b985692e-6338-46c7-8cea-bc38996d4dfd]
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description = "decode received messages -> 0xcf4b00 is decoded to 0xce94"
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[7a1f4d48-696d-4679-917c-21b7da3ff3fd]
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description = "decode received messages -> 0xe2566500 is decoded to 0xe2ad90"
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[467549dc-a558-443b-80c5-ff3d4eb305d4]
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description = "decode received messages -> six byte message"
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[1f3be5fb-093a-4661-9951-c1c4781c71ea]
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description = "decode received messages -> seven byte message"
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[6065b8b3-9dcd-45c9-918c-b427cfdb28c1]
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description = "decode received messages -> last byte has wrong parity"
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[98af97b7-9cca-4c4c-9de3-f70e227a4cb1]
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description = "decode received messages -> eight byte message"
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[aa7d4785-2bb9-43a4-a38a-203325c464fb]
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description = "decode received messages -> twenty byte message"
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[4c86e034-b066-42ac-8497-48f9bc1723c1]
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description = "decode received messages -> wrong parity on 16th byte"

‎exercises/practice/intergalactic-transmission/Makefile

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AS = nasm
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CFLAGS = -g -Wall -Wextra -pedantic -Werror
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LDFLAGS =
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ASFLAGS = -g -F dwarf -Werror
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ifeq ($(shell uname -s),Darwin)
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ifeq ($(shell sysctl -n hw.optional.arm64 2>/dev/null),1)
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ALL_CFLAGS = -target x86_64-apple-darwin
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endif
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ALL_LDFLAGS = -Wl,-pie
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ALL_ASFLAGS = -f macho64 --prefix _
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else
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ALL_LDFLAGS = -pie -Wl,--fatal-warnings
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ALL_ASFLAGS = -f elf64
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endif
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ALL_CFLAGS += -std=c99 -fPIE -m64 $(CFLAGS)
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ALL_LDFLAGS += $(LDFLAGS)
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ALL_ASFLAGS += $(ASFLAGS)
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C_OBJS = $(patsubst %.c,%.o,$(wildcard *.c))
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AS_OBJS = $(patsubst %.asm,%.o,$(wildcard *.asm))
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ALL_OBJS = $(filter-out example.o,$(C_OBJS) $(AS_OBJS) vendor/unity.o)
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CC_CMD = $(CC) $(ALL_CFLAGS) -c -o $@ $<
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all: tests
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@./$<
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tests: $(ALL_OBJS)
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@$(CC) $(ALL_CFLAGS) $(ALL_LDFLAGS) -o $@ $(ALL_OBJS)
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%.o: %.asm
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@$(AS) $(ALL_ASFLAGS) -o $@ $<
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%.o: %.c
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@$(CC_CMD)
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vendor/unity.o: vendor/unity.c vendor/unity.h vendor/unity_internals.h
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@$(CC_CMD)
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clean:
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@rm -f *.o vendor/*.o tests
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.PHONY: all clean

‎exercises/practice/intergalactic-transmission/intergalactic_transmission.asm

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section .text
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global transmit_sequence, decode_message
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transmit_sequence:
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; Provide your implementation here
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ret
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decode_message:
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; Provide your implementation here
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ret
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%ifidn __OUTPUT_FORMAT__,elf64
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section .note.GNU-stack noalloc noexec nowrite progbits
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%endif

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