[{"_1":2,"_3":-5,"_4":-5},"loaderData",{"_5":6,"_7":8},"actionData","errors","root",{"_26":27,"_28":29,"_30":12,"_31":12,"_32":12,"_33":29,"_34":12,"_35":12,"_36":12,"_37":12,"_38":-5,"_39":40},"routes/canvas.shared.$sharedTextdocId",{"_9":10,"_11":12},"sharedTextdoc",{"_13":14,"_15":-7,"_16":17,"_18":19,"_20":21,"_22":23,"_24":12,"_25":12},"isAuthenticated",false,"sharedTextdocId","690c3bb2c7fc81919e07ec62c63fc0ad","versionInt","title","Parity & Checksum Error-detection Playground","type","code/react","content","import React, { useMemo, useState } from \"react\";\nimport { Card, CardContent } from \"@/components/ui/card\";\nimport { Label } from \"@/components/ui/label\";\nimport { motion } from \"framer-motion\";\n\n// ----------------- Bit helpers -----------------\nfunction textToBytes(str: string): number[] {\n return Array.from(new TextEncoder().encode(str));\n}\nfunction byteToBits(b: number): number[] {\n const bits = new Array(8).fill(0);\n for (let i = 0; i < 8; i++) bits[7 - i] = (b >> i) & 1;\n return bits;\n}\nfunction bitsToByte(bits: number[]): number {\n let v = 0;\n for (let i = 0; i < 8; i++) v = (v << 1) | (bits[i] & 1);\n return v & 0xff;\n}\nfunction addNoise(bits: number[], p: number): number[] {\n return bits.map((bit) => (Math.random() < p ? 1 - bit : bit));\n}\n\n// ----------------- FEC: variable redundancy via per-bit repetition -----------------\n// Each payload bit is repeated reps[i] times (odd), and recovered by majority vote.\nfunction repsForByte(fecBitsPerByte: number): number[] {\n const base = Math.floor(fecBitsPerByte / 8);\n let extra = fecBitsPerByte % 8;\n const reps = new Array(8).fill(1 + base);\n for (let i = 0; i < 8; i++) {\n if (extra > 0) {\n reps[i] += 1;\n extra--;\n }\n if (reps[i] % 2 === 0) reps[i] += 1; // force odd to avoid ties\n }\n return reps; // sum(reps) = 8 + fecBitsPerByte (+ up to 8 from odd forcing)\n}\n\nfunction encodeFECVariable(payloadBytes: number[], fecBitsPerByte: number): { bits: number[]; groupSizes: number[] } {\n const out: number[] = [];\n const reps = repsForByte(fecBitsPerByte);\n const groupSizes: number[] = [];\n for (const b of payloadBytes) {\n const data = byteToBits(b);\n for (let i = 0; i < 8; i++) {\n for (let r = 0; r < reps[i]; r++) out.push(data[i]);\n groupSizes.push(reps[i]);\n }\n }\n return { bits: out, groupSizes };\n}\n\ntype DecodeStats = {\n detectedError: boolean;\n correctedAny: boolean;\n payloadBytes: number[];\n effectiveOverhead: number; // bits per encoded byte minus 8\n groupsTotal: number;\n groupsWithFlips: number;\n groupsCorrected: number; // flips present and majority recovered original bit\n groupsFailed: number; // flips present and majority chose wrong bit\n bytesIncorrect: number; // decoded byte != original byte\n};\n\nfunction decodeFECVariable(rxBits: number[], fecBitsPerByte: number, txBits: number[], originalBytes: number[]): DecodeStats {\n const reps = repsForByte(fecBitsPerByte);\n const stride = reps.reduce((a, b) => a + b, 0); // bits per encoded byte\n const out: number[] = [];\n let detectedError = false;\n let correctedAny = false;\n let ptr = 0;\n\n let groupsTotal = 0;\n let groupsWithFlips = 0;\n let groupsCorrected = 0;\n let groupsFailed = 0;\n let bytesIncorrect = 0;\n\n for (let byteIdx = 0; byteIdx < originalBytes.length; byteIdx++) {\n const dataBits: number[] = [];\n let anyGroupFlip = false;\n let anyGroupWrong = false;\n for (let i = 0; i < 8; i++) {\n const R = reps[i];\n const groupRx = rxBits.slice(ptr, ptr + R);\n const groupTx = txBits.slice(ptr, ptr + R); // all equal to original bit\n ptr += R;\n groupsTotal++;\n\n const ones = groupRx.reduce((a, b) => a + b, 0);\n const zeros = R - ones;\n const majority = ones >= zeros ? 1 : 0; // ties impossible\n const originalBit = groupTx[0];\n\n const flipsHappened = ones !== 0 && zeros !== 0;\n if (flipsHappened) {\n groupsWithFlips++;\n anyGroupFlip = true;\n detectedError = true;\n if (majority === originalBit) {\n groupsCorrected++;\n correctedAny = true;\n } else {\n groupsFailed++;\n anyGroupWrong = true;\n }\n }\n\n dataBits.push(majority);\n }\n const decodedByte = bitsToByte(dataBits);\n out.push(decodedByte);\n if (decodedByte !== originalBytes[byteIdx]) bytesIncorrect++;\n }\n\n const effectiveOverhead = stride - 8;\n return { detectedError, correctedAny, payloadBytes: out, effectiveOverhead, groupsTotal, groupsWithFlips, groupsCorrected, groupsFailed, bytesIncorrect };\n}\n\nexport default function App() {\n // Fixed requirements: always 8 bytes (\"MESSAGES\").\n const text = \"MESSAGES\";\n\n const [bitError, setBitError] = useState(0.01);\n const [fecBits, setFecBits] = useState(8); // requested extra FEC bits per payload byte\n const [bitView, setBitView] = useState(false);\n\n const bytes = useMemo(() => textToBytes(text), []);\n\n const { txBits, rxBits, decoded } = useMemo(() => {\n const enc = encodeFECVariable(bytes, fecBits);\n const noisy = addNoise(enc.bits, bitError);\n const dec = decodeFECVariable(noisy, fecBits, enc.bits, bytes);\n return { txBits: enc.bits, rxBits: noisy, decoded: dec };\n }, [bytes, fecBits, bitError]);\n\n const originalBits = useMemo(() => txBits.join(\"\"), [txBits]);\n const receivedBits = useMemo(() => rxBits.join(\"\"), [rxBits]);\n\n const codeRate = useMemo(() => {\n const reps = repsForByte(fecBits);\n const stride = reps.reduce((a, b) => a + b, 0);\n return 8 / stride;\n }, [fecBits]);\n\n const pct = (num: number, den: number) => (den === 0 ? 0 : (100 * num) / den);\n\n return (\n

\n \n FEC Error Visualization (8-byte message)\n \n\n

\n \n \n

\n Bit error rate (E)\n setBitError(parseFloat(e.target.value))} className=\"w-full\" />\n

E = {bitError.toFixed(4)}

\n\n

\n FEC extra bits per payload byte\n setFecBits(parseInt(e.target.value || \"0\"))} className=\"w-full\" />\n

requested = {fecBits} | effective (odd groups) = {decoded.effectiveOverhead}

Extra bits are distributed across the 8 data bits and each bit is repeated with an odd count for safe majority decoding.

\n\n

\n setBitView(e.target.checked)} />\n Bit-level view\n

\n\n

Code rate: {codeRate.toFixed(3)} (payload/encoded)

Lower rate ⇒ more redundancy ⇒ higher correction capability.

\n \n \n\n \n \n {bitView ? (\n

Original bits:

{originalBits}

Received bits:

\n {receivedBits.split(\"\").map((b, i) => (\n {b}\n ))}\n

\n ) : (\n

Original text:

{\"MESSAGES\"}

Received text:

\n {String.fromCharCode(...decoded.payloadBytes).split(\"\").map((c, i) => (\n {c}\n ))}\n

\n )}\n\n

Detected any flips: {decoded.detectedError ? \"yes\" : \"no\"}

\n Bit-groups corrected:\n {\" \"}\n {decoded.groupsCorrected}/{decoded.groupsWithFlips} ({pct(decoded.groupsCorrected, decoded.groupsWithFlips).toFixed(1)}%)\n

\n Bit-groups uncorrectable:\n {\" \"}\n {decoded.groupsFailed}/{decoded.groupsWithFlips} ({pct(decoded.groupsFailed, decoded.groupsWithFlips).toFixed(1)}%)\n

\n Bytes incorrect after decode:\n {\" \"}\n {decoded.bytesIncorrect}/8 ({pct(decoded.bytesIncorrect, 8).toFixed(1)}%)\n

A \"bit-group\" is the repetition block for one payload bit. \"Uncorrectable\" means more than half of a group flipped.

\n \n \n

\n );\n}\n","access","public","isModerationBlocked","isAnonifyApiKeyDetected","dd",{"_41":42,"_43":44},"disablePrefetch",true,"shouldPrefetchAccount","shouldPrefetchUser","shouldPrefetchSystemHints","manageRootRouteStylesheet","mobileWebHandoffEnabled","promoteCss","disableSSR","stripModulepreloadImports","paidCampaignAppRedirect","statsigGateEvaluationsPromise",["P",40],"traceId","7847795672904685465","traceTime",1789573971467]