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/** |
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* gint: Generic integer. |
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* A class to represent any integer from 1 to 53-Bit. |
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* Copyright (c) 2017 Rafael da Silva Rocha. |
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* https://github.com/rochars/byte-data |
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*/ |
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/** |
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* A class to represent any integer from 1 to 53-Bit. |
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*/ |
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class GInt { |
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/** |
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* @param {Object} options The type definition. |
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* @param {number} options.bits Number of bits used by data of this type. |
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* @param {boolean} options.be True for big-endian. |
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* @param {boolean} options.signed True for signed types. |
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*/ |
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constructor(options) { |
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/** |
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* The max number of bits used by data of this type. |
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* @type {number} |
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*/ |
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this.bits = options["bits"]; |
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/** |
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* If this type is big-endian or not. |
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* @type {boolean} |
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*/ |
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this.be = options["be"]; |
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/** |
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* If this type it is signed or not. |
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* @type {boolean} |
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*/ |
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this.signed = options["signed"]; |
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/** |
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* The base used to represent data of this type. |
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* Default is 10. |
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* @type {number} |
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*/ |
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this.base = options["base"] ? options["base"] : 10; |
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/** |
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* The function to read values of this type from buffers. |
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* @type {Function} |
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* @ignore |
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*/ |
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this.reader = this.read_; |
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/** |
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* The function to write values of this type to buffers. |
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* @type {Function} |
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* @ignore |
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*/ |
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this.writer = this.write_; |
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/** |
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* The number of bytes used by data of this type. |
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* @type {number} |
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* @ignore |
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*/ |
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this.offset = 0; |
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/** |
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* Min value for numbers of this type. |
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* @type {number} |
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* @ignore |
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*/ |
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this.min = -Infinity; |
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/** |
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* Max value for numbers of this type. |
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* @type {number} |
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* @ignore |
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*/ |
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this.max = Infinity; |
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/** |
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* The word size. |
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* @type {number} |
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* @ignore |
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*/ |
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this.realBits = this.bits; |
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/** |
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* The mask to be used in the last byte of this type. |
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* @type {number} |
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* @ignore |
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*/ |
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this.lastByteMask = 255; |
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this.build_(); |
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} |
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/** |
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* Sign a number according to the type. |
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* @param {number} num The number. |
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* @return {number} |
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* @ignore |
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*/ |
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sign(num) { |
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if (num > this.max) { |
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num -= (this.max * 2) + 2; |
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} |
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return num; |
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} |
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/** |
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* Limit the value according to the bit depth in case of |
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* overflow or underflow. |
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* @param {number} value The data. |
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* @return {number} |
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* @ignore |
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*/ |
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overflow(value) { |
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if (value > this.max) { |
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value = this.max; |
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} else if (value < this.min) { |
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value = this.min; |
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} |
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return value; |
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} |
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/** |
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* Read a integer number from a byte buffer. |
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* @param {!Array<number>|Uint8Array} bytes An array of bytes. |
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* @param {number} i The index to read. |
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* @param {Object} type The type if other than this. |
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* @return {number} |
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* @private |
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*/ |
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read_(bytes, i, type=this) { |
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let num = 0; |
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let x = type.offset - 1; |
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while (x > 0) { |
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num = (bytes[x + i] << x * 8) | num; |
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x--; |
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} |
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num = (bytes[i] | num) >>> 0; |
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return this.overflow(this.sign(num)); |
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} |
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/** |
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* Read a integer number from a byte buffer by turning the bytes |
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* to a string of bits. |
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* @param {!Array<number>|Uint8Array} bytes An array of bytes. |
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* @param {number} i The index to read. |
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* @param {Object} type The type if other than this. |
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* @return {number} |
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* @private |
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*/ |
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readBits_(bytes, i, type=this) { |
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let binary = ""; |
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let j = 0; |
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while(j < type.offset) { |
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let bits = bytes[i + j].toString(2); |
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binary = Array(9 - bits.length).join("0") + bits + binary; |
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j++; |
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} |
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return this.overflow(this.sign(parseInt(binary, 2))); |
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} |
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/** |
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* Write one integer number to a byte buffer. |
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* @param {!Array<number>} bytes An array of bytes. |
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* @param {number} number The number. |
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* @param {number} j The index being written in the byte buffer. |
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* @param {Object} type The type. |
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* @return {number} The next index to write on the byte buffer. |
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* @private |
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*/ |
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write_(bytes, number, j, type=this) { |
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number = this.overflow(number); |
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let mask = 255; |
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let len = type.offset; |
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j = this.writeFirstByte_(bytes, number, j, type); |
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for (let i = 2; i <= len; i++) { |
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if (i == len) { |
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mask = type.lastByteMask; |
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} |
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bytes[j++] = Math.floor(number / Math.pow(2, ((i - 1) * 8))) & mask; |
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} |
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return j; |
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} |
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/** |
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* Build the type. |
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* @private |
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*/ |
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build_() { |
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this.validateWordSize_(); |
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this.setRealBits_(); |
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this.setLastByteMask_(); |
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this.setMinMax_(); |
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this.offset = this.bits < 8 ? 1 : Math.ceil(this.realBits / 8); |
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} |
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/** |
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* Set the minimum and maximum values for the type. |
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* @private |
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*/ |
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setMinMax_() { |
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let max = Math.pow(2, this.bits); |
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if (this.signed) { |
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this.max = max / 2 -1; |
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this.min = -max / 2; |
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} else { |
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this.max = max - 1; |
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this.min = 0; |
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} |
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} |
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validateWordSize_() { |
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if (this.bits < 1 || this.bits > 64) { |
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throw Error("Not a supported type."); |
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} |
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} |
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/** |
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* Set the real bit depth for data with bit count different from the |
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* standard types (1, 2, 4, 8, 16, 32, 40, 48, 64): the closest bigger |
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* standard number of bits. The data is then treated as data of the |
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* standard type on all aspects except for the min and max values. |
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* Ex: a 11-bit uInt is treated as 16-bit uInt with a max value of 2048. |
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* @private |
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*/ |
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setRealBits_() { |
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if (this.bits > 8) { |
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if (this.bits <= 16) { |
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this.realBits = 16; |
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} else if (this.bits <= 24) { |
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this.realBits = 24; |
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} else if (this.bits <= 32) { |
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this.realBits = 32; |
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} else if (this.bits <= 40) { |
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this.realBits = 40; |
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} else if (this.bits <= 48) { |
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this.realBits = 48; |
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} else if (this.bits <= 56) { |
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this.realBits = 56; |
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} else { |
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this.realBits = 64; |
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} |
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} else { |
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this.realBits = this.bits; |
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} |
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} |
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/** |
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* Set the mask that should be used when writing the last byte of |
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* data of the type. |
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* @private |
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*/ |
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setLastByteMask_() { |
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let r = 8 - (this.realBits - this.bits); |
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this.lastByteMask = Math.pow(2, r > 0 ? r : 8) -1; |
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} |
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/** |
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* Write the first byte of a integer number. |
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* @param {!Array<number>} bytes An array of bytes. |
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* @param {number} number The number. |
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* @param {number} j The index being written in the byte buffer. |
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* @param {Object} type The type. |
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* @return {number} The next index to write on the byte buffer. |
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* @private |
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*/ |
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writeFirstByte_(bytes, number, j, type=this) { |
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if (type.bits < 8) { |
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bytes[j++] = number < 0 ? number + Math.pow(2, type.bits) : number; |
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} else { |
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bytes[j++] = number & 255; |
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} |
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return j; |
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} |
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} |
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module.exports = GInt; |
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