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claus/base64fixer.js

Created August 25, 2021 19:12
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Revisions

  1. claus revised this gist Aug 25, 2021. No changes.
  2. claus created this gist Aug 25, 2021.
    60 changes: 60 additions & 0 deletions base64fixer.js
    View file
    Original file line number Diff line number Diff line change
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    const b64alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
    const b64 = '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'.toUpperCase();
    const b64arr = b64.split('');

    function getBestMatch(quad) {
    const scores = [];
    let cancelled = false;
    for (let i = 0; i < 16; i++) {
    const bin = i.toString(2).padStart(4, '0');
    const res = new Array(3).fill(0);
    let resb64 = '';
    for (let j = 0; j < 4; j++) {
    try {
    const b = bin[j] === '0' ? quad[j].toLowerCase() : quad[j];
    const b6 = b64alphabet.indexOf(b);
    if (j === 0) {
    res[0] = b6 << 2; // 543210xx
    } else if (j === 1) {
    res[0] = res[0] | (b6 >> 4); // xxxxxx54
    res[1] = (b6 << 4) & 255; // 3210xxxx
    } else if (j === 2) {
    res[1] = res[1] | (b6 >> 2); // xxxx5432
    res[2] = (b6 << 6) & 255; // 10xxxxxx
    } else if (j === 3) {
    res[2] = res[2] | b6; // xx543210
    }
    resb64 += b;
    } catch (e) {
    console.log(`cancelled ${i} ${j}`);
    cancelled = true;
    j = 4;
    i = 16;
    }
    }
    const score = res.reduce((a, v) => {
    return v >= 0x20 && v <= 0x7a ? a + 1 : a;
    }, 0);
    scores.push({
    score,
    res,
    resb64,
    });
    }
    const best = scores.sort((a, b) => b.score - a.score)[0];
    return { ...best, cancelled };
    }

    let pos = 0;
    let resultb64 = '';
    while (pos < b64arr.length) {
    const quad = b64arr.slice(pos, pos + 4);
    const best = getBestMatch(quad);
    if (best.cancelled) {
    console.log(`cancelled at ${pos} from ${b64arr.length}`)
    }
    resultb64 += best.resb64;
    pos += 4;
    }

    console.log(resultb64);