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102 lines
2.8 KiB
102 lines
2.8 KiB
// IEEE754 conversions based on https://github.com/feross/ieee754 |
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var $Array = Array; |
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var abs = Math.abs; |
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var pow = Math.pow; |
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var floor = Math.floor; |
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var log = Math.log; |
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var LN2 = Math.LN2; |
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var pack = function (number, mantissaLength, bytes) { |
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var buffer = $Array(bytes); |
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var exponentLength = bytes * 8 - mantissaLength - 1; |
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var eMax = (1 << exponentLength) - 1; |
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var eBias = eMax >> 1; |
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var rt = mantissaLength === 23 ? pow(2, -24) - pow(2, -77) : 0; |
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var sign = number < 0 || number === 0 && 1 / number < 0 ? 1 : 0; |
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var index = 0; |
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var exponent, mantissa, c; |
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number = abs(number); |
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// eslint-disable-next-line no-self-compare -- NaN check |
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if (number != number || number === Infinity) { |
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// eslint-disable-next-line no-self-compare -- NaN check |
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mantissa = number != number ? 1 : 0; |
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exponent = eMax; |
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} else { |
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exponent = floor(log(number) / LN2); |
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c = pow(2, -exponent); |
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if (number * c < 1) { |
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exponent--; |
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c *= 2; |
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} |
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if (exponent + eBias >= 1) { |
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number += rt / c; |
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} else { |
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number += rt * pow(2, 1 - eBias); |
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} |
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if (number * c >= 2) { |
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exponent++; |
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c /= 2; |
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} |
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if (exponent + eBias >= eMax) { |
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mantissa = 0; |
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exponent = eMax; |
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} else if (exponent + eBias >= 1) { |
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mantissa = (number * c - 1) * pow(2, mantissaLength); |
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exponent = exponent + eBias; |
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} else { |
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mantissa = number * pow(2, eBias - 1) * pow(2, mantissaLength); |
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exponent = 0; |
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} |
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} |
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while (mantissaLength >= 8) { |
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buffer[index++] = mantissa & 255; |
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mantissa /= 256; |
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mantissaLength -= 8; |
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} |
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exponent = exponent << mantissaLength | mantissa; |
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exponentLength += mantissaLength; |
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while (exponentLength > 0) { |
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buffer[index++] = exponent & 255; |
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exponent /= 256; |
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exponentLength -= 8; |
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} |
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buffer[--index] |= sign * 128; |
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return buffer; |
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}; |
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var unpack = function (buffer, mantissaLength) { |
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var bytes = buffer.length; |
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var exponentLength = bytes * 8 - mantissaLength - 1; |
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var eMax = (1 << exponentLength) - 1; |
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var eBias = eMax >> 1; |
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var nBits = exponentLength - 7; |
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var index = bytes - 1; |
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var sign = buffer[index--]; |
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var exponent = sign & 127; |
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var mantissa; |
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sign >>= 7; |
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while (nBits > 0) { |
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exponent = exponent * 256 + buffer[index--]; |
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nBits -= 8; |
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} |
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mantissa = exponent & (1 << -nBits) - 1; |
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exponent >>= -nBits; |
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nBits += mantissaLength; |
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while (nBits > 0) { |
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mantissa = mantissa * 256 + buffer[index--]; |
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nBits -= 8; |
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} |
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if (exponent === 0) { |
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exponent = 1 - eBias; |
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} else if (exponent === eMax) { |
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return mantissa ? NaN : sign ? -Infinity : Infinity; |
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} else { |
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mantissa = mantissa + pow(2, mantissaLength); |
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exponent = exponent - eBias; |
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} return (sign ? -1 : 1) * mantissa * pow(2, exponent - mantissaLength); |
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}; |
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module.exports = { |
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pack: pack, |
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unpack: unpack |
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};
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