JS parser for Float Hex notation

hex-float-parser.js

function floatToWord(f) {
    let b = new ArrayBuffer(4)
    let iView = new Uint32Array(b)
    let fView = new Float32Array(b)
    fView[0] = f
    return iView[0]
}

function wordToFloat(w) {
    let b = new ArrayBuffer(4)
    let iView = new Uint32Array(b)
    let fView = new Float32Array(b)
    iView[0] = w
    return fView[0]
}

function readHexFloat(str) {
    var [_, sign, int, _, frac, _, expStr] = /^([+-]?)0x([0-9a-f]*)(\.([0-9a-f]*))?([pP]([+-]?\d*))?$/.exec(str.toLowerCase())
    let exp = parseInt(expStr || '0', 10)
    int = int.replace(/^0*/, '') || '0'
    frac = (frac || '').replace(/0*$/, '') || '0'
    let w = sign === '-' ? 0x80000000 : 0
    if (parseInt(int, 16)) {
        frac = int + frac
        exp += int.length * 4
    }
    if (parseInt(frac, 16) === 0) {
        return wordToFloat(w)
    }
    let hexFracWithoutLeadingZeros = frac.replace(/^0*/, '')
    exp -= (frac.length - hexFracWithoutLeadingZeros.length) * 4
    let binFrac = parseInt(frac, 16).toString(2)
    exp -= hexFracWithoutLeadingZeros.length * 4 - binFrac.length + 1
    binFrac = binFrac.replace(/0*$/, '')
    const budget = Math.min(24, 150 + exp)
    if (binFrac.length > budget) {
        let roundedFrac = binFrac.slice(0, budget)
        let rest = binFrac.slice(budget)
        if (rest[0] === '1' && (rest.length > 1 || roundedFrac[roundedFrac.length - 1] === '1')) {
            if (roundedFrac.length === roundedFrac.replace('0', '').length) {
                exp++
                binFrac = '1'
            }
            else {
                binFrac = (parseInt(roundedFrac, 2) + 1).toString(2)
            }
        }
        else {
            binFrac = roundedFrac
        }
    }
    if (exp < -150 || exp > 127) {
        throw Error('Constant out of range: ' + exp)
    }
    if (exp >= -126) {
        w = w | ((exp + 127) << 23) | (parseInt(binFrac.slice(1) || '0', 2) << (24 - binFrac.length))
    }
    else {
        const shift = 150 - binFrac.length - Math.abs(exp)
        if (shift < 0) {
            return wordToFloat(w)
        }
        w = w | (parseInt(binFrac, 2) << (150 - binFrac.length - Math.abs(exp)))
    }
    return wordToFloat(w)
}