85 lines
2.1 KiB
JavaScript
85 lines
2.1 KiB
JavaScript
exports.readIEEE754 = function(buffer, offset, isBE, mLen, nBytes) {
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var e, m,
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eLen = nBytes * 8 - mLen - 1,
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eMax = (1 << eLen) - 1,
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eBias = eMax >> 1,
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nBits = -7,
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i = isBE ? 0 : (nBytes - 1),
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d = isBE ? 1 : -1,
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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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exports.writeIEEE754 = function(buffer, value, offset, isBE, mLen, nBytes) {
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var e, m, c,
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eLen = nBytes * 8 - mLen - 1,
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eMax = (1 << eLen) - 1,
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eBias = eMax >> 1,
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rt = (mLen === 23 ? Math.pow(2, -24) - Math.pow(2, -77) : 0),
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i = isBE ? (nBytes - 1) : 0,
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d = isBE ? -1 : 1,
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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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