85 lines
2.0 KiB
JavaScript
85 lines
2.0 KiB
JavaScript
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export function read(buffer, offset, isLE, mLen, nBytes) {
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var e, m
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var eLen = (nBytes * 8) - mLen - 1
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var eMax = (1 << eLen) - 1
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var eBias = eMax >> 1
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var nBits = -7
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var i = isLE ? (nBytes - 1) : 0
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var d = isLE ? -1 : 1
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var s = buffer[offset + i]
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i += d
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e = s & ((1 << (-nBits)) - 1)
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s >>= (-nBits)
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nBits += eLen
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for (; nBits > 0; e = (e * 256) + buffer[offset + i], i += d, nBits -= 8) {}
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m = e & ((1 << (-nBits)) - 1)
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e >>= (-nBits)
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nBits += mLen
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for (; nBits > 0; m = (m * 256) + buffer[offset + i], i += d, nBits -= 8) {}
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if (e === 0) {
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e = 1 - eBias
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} else if (e === eMax) {
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return m ? NaN : ((s ? -1 : 1) * Infinity)
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} else {
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m = m + Math.pow(2, mLen)
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e = e - eBias
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}
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return (s ? -1 : 1) * m * Math.pow(2, e - mLen)
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}
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export function write(buffer, value, offset, isLE, mLen, nBytes) {
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var e, m, c
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var eLen = (nBytes * 8) - mLen - 1
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var eMax = (1 << eLen) - 1
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var eBias = eMax >> 1
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var rt = (mLen === 23 ? Math.pow(2, -24) - Math.pow(2, -77) : 0)
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var i = isLE ? 0 : (nBytes - 1)
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var d = isLE ? 1 : -1
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var s = value < 0 || (value === 0 && 1 / value < 0) ? 1 : 0
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value = Math.abs(value)
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if (isNaN(value) || value === Infinity) {
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m = isNaN(value) ? 1 : 0
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e = eMax
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} else {
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e = Math.floor(Math.log(value) / Math.LN2)
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if (value * (c = Math.pow(2, -e)) < 1) {
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e--
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c *= 2
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}
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if (e + eBias >= 1) {
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value += rt / c
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} else {
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value += rt * Math.pow(2, 1 - eBias)
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}
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if (value * c >= 2) {
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e++
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c /= 2
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}
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if (e + eBias >= eMax) {
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m = 0
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e = eMax
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} else if (e + eBias >= 1) {
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m = ((value * c) - 1) * Math.pow(2, mLen)
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e = e + eBias
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} else {
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m = value * Math.pow(2, eBias - 1) * Math.pow(2, mLen)
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e = 0
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}
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}
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for (; mLen >= 8; buffer[offset + i] = m & 0xff, i += d, m /= 256, mLen -= 8) {}
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e = (e << mLen) | m
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eLen += mLen
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for (; eLen > 0; buffer[offset + i] = e & 0xff, i += d, e /= 256, eLen -= 8) {}
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buffer[offset + i - d] |= s * 128
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}
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