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/** |
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* type: The Type class. |
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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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/** @private */ |
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let f32 = new Float32Array(1); |
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/** @private */ |
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let i32 = new Int32Array(f32.buffer); |
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/** @private */ |
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let f64 = new Float64Array(1); |
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/** @private */ |
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let ui32 = new Uint32Array(f64.buffer); |
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/** |
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* Functions to read data from bytes. |
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* @enum {Function} |
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*/ |
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const BitReader = { |
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"read": function(bytes, i, type) { |
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let num = 0; |
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let z = 1; |
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let x = type.offset; |
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/* |
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if (type.bits < 33) { |
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for (let x = type.offset; x > 0; x--) { |
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if (x > 1) { |
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num = bytes[x + i] << ((i - 1) * 8) | num; |
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} else { |
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num = (bytes[i] | num); |
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} |
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z++; |
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} |
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*/ |
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//} else { |
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num = readBytesAsBits(bytes, i, type.offset); |
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//} |
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return num; |
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}, |
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/** |
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* Read 1 16-bit float from from bytes. |
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* Thanks https://stackoverflow.com/a/8796597 |
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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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* @return {number} |
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*/ |
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"read16F": function (bytes, i) { |
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let binary = parseInt(getBinary([bytes[i], bytes[i+1]]), 2); |
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let exponent = (binary & 0x7C00) >> 10; |
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let fraction = binary & 0x03FF; |
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let floatValue; |
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if (exponent) { |
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floatValue = Math.pow(2, exponent - 15) * (1 + fraction / 0x400); |
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} else { |
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floatValue = 6.103515625e-5 * (fraction / 0x400); |
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} |
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return floatValue * (binary >> 15 ? -1 : 1); |
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}, |
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/** |
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* Read 1 32-bit float from from bytes. |
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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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* @return {number} |
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*/ |
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"read32F": function (bytes, i) { |
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i32[0] = BitReader["read"](bytes, i, {"offset": 4}); |
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return f32[0]; |
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}, |
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/** |
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* Read 1 64-bit double from bytes. |
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* Thanks https://gist.github.com/kg/2192799 |
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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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* @return {number} |
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*/ |
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"read64F": function (bytes, i) { |
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let type = {"bits": 32, "offset": 4}; |
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ui32[0] = BitReader["read"](bytes, i, type); |
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ui32[1] = BitReader["read"](bytes, i + 4, type); |
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return f64[0]; |
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}, |
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/** |
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* Read 1 char from bytes. |
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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 index to read. |
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* @return {string} |
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*/ |
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"readChar": function (bytes, i, type) { |
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let chrs = ""; |
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let j = 0; |
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let len = type.bits / 8; |
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while(j < len) { |
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chrs += String.fromCharCode(bytes[i+j]); |
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j++; |
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} |
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return chrs; |
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} |
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}; |
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/** |
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* Functions to write data to bytes. |
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* @enum {Function} |
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*/ |
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let BitWriter = { |
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/** |
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* Write one 64-bit float as a binary value. |
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* @param {!Array<number>} bytes An array of bytes. |
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* @param {number} number The number to write as bytes. |
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* @param {number} j The index being written in the byte buffer. |
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* @return {number} The next index to write on the byte buffer. |
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*/ |
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"write64F": function(bytes, number, j) { |
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f64[0] = number; |
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let type = {bits: 32, offset: 4, lastByteMask:255}; |
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j = BitWriter["write"](bytes, ui32[0], j, type); |
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return BitWriter["write"](bytes, ui32[1], j, type); |
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}, |
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/** |
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* Write one 32-bit float as a binary value. |
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* @param {!Array<number>} bytes An array of bytes. |
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* @param {number} number The number to write as bytes. |
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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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*/ |
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"write32F": function (bytes, number, j, type) { |
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f32[0] = number; |
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j = BitWriter["write"](bytes, i32[0], j, type); |
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return j; |
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}, |
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/** |
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* Write one 16-bit float as a binary value. |
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* @param {!Array<number>} bytes An array of bytes. |
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* @param {number} number The number to write as bytes. |
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* @param {number} j The index being written in the byte buffer. |
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* @return {number} The next index to write on the byte buffer. |
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*/ |
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"write16F": function (bytes, number, j) { |
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f32[0] = number; |
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let x = i32[0]; |
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let bits = (x >> 16) & 0x8000; |
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let m = (x >> 12) & 0x07ff; |
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let e = (x >> 23) & 0xff; |
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if (e >= 103) { |
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bits |= ((e - 112) << 10) | (m >> 1); |
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bits += m & 1; |
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} |
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bytes[j++] = bits & 0xFF; |
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bytes[j++] = bits >>> 8 & 0xFF; |
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return j; |
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}, |
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/** |
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* Write one char as a byte. |
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* @param {!Array<number>} bytes An array of bytes. |
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* @param {string} string The string to write as bytes. |
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* @param {number} j The index being written in the byte buffer. |
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* @return {number} The next index to write on the byte buffer. |
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*/ |
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"writeString": function (bytes, string, j) { |
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bytes[j++] = string.charCodeAt(0); |
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return j; |
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}, |
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/** |
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* Write one char as a byte. |
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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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*/ |
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"write": function (bytes, number, j, type) { |
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let mask = 255; |
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let len = type.offset; |
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for (let i = 1; i <= len; i++) { |
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if (i == 1) { |
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j = writeFirstByte(bytes, number, j, type); |
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} else { |
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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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} |
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return j; |
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} |
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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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*/ |
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function writeFirstByte(bytes, number, j, type) { |
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if (type.offset == 1 && 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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* A class to represent byte-data types. |
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*/ |
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class Type { |
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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.char True for string/char types. |
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* @param {boolean} options.float True for float types. |
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* Available only for 16, 32 and 64-bit data. |
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* @param {boolean} options.be True for signed types. |
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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 represent floating-point values or not. |
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* @type {boolean} |
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*/ |
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this.char = options["char"]; |
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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.float = options["float"]; |
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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 = this.float ? true : options["signed"]; |
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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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*/ |
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this.reader = null; |
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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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*/ |
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this.writer = null; |
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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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*/ |
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this.offset = 0; |
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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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* Min value for numbers of this type. |
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* @type {number} |
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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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*/ |
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this.max = Infinity; |
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this.realBits = this.bits; |
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this.lastByteMask = 255; |
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this.build_(); |
292
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} |
293
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294
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/** |
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* Sign a number according to the type. |
296
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* @param {number} num The number. |
297
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* @return {number} |
298
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*/ |
299
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sign(num) { |
300
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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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306
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/** |
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* Limit the value according to the bit depth in case of |
308
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* overflow or underflow. |
309
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* @param {number} value The data. |
310
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* @return {number} |
311
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*/ |
312
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overflow(value) { |
313
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if (value > this.max) { |
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value = this.max; |
315
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} else if (value < this.min) { |
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value = this.min; |
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} |
318
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return value; |
319
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} |
320
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321
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/** |
322
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* Build the type. |
323
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* @private |
324
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*/ |
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build_() { |
326
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this.setRealBits_(); |
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this.setLastByteMask_(); |
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this.offset = this.bits < 8 ? 1 : Math.ceil(this.realBits / 8); |
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this.setReader_(); |
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this.setWriter_(); |
331
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if (!this.float) { |
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this.setMinMax_(); |
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} |
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} |
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336
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/** |
337
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* Set the function to read data of this type. |
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* @private |
339
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*/ |
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setReader_() { |
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if (this.float) { |
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this.reader = BitReader[ |
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'read' + this.bits + 'F']; |
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} else if (this.char) { |
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this.reader = BitReader["readChar"]; |
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} else { |
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this.reader = BitReader["read"]; |
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} |
349
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} |
350
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351
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/** |
352
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* Set the function to write data of this type. |
353
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* @private |
354
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*/ |
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setWriter_() { |
356
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if (this.char) { |
357
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this.writer = BitWriter["writeString"]; |
358
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} else if (this.float) { |
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this.writer = BitWriter[ |
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'write' + this.realBits + 'F']; |
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} else { |
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this.writer = BitWriter["write"]; |
363
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} |
364
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} |
365
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366
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/** |
367
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* Set the minimum and maximum values for the type. |
368
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* @private |
369
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*/ |
370
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setMinMax_() { |
371
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|
|
let max = Math.pow(2, this.bits); |
372
|
|
|
if (this.signed) { |
373
|
|
|
this.max = max / 2 -1; |
374
|
|
|
this.min = -max / 2; |
375
|
|
|
} else { |
376
|
|
|
this.max = max - 1; |
377
|
|
|
this.min = 0; |
378
|
|
|
} |
379
|
|
|
} |
380
|
|
|
|
381
|
|
|
/** |
382
|
|
|
* Set the real bit depth for data with bit count different from the |
383
|
|
|
* standard types (1, 2, 4, 8, 16, 32, 40, 48, 64): the closest bigger |
384
|
|
|
* standard number of bits. The data is then treated as data of the |
385
|
|
|
* standard type on all aspects except for the min and max values. |
386
|
|
|
* Ex: a 11-bit uInt is treated as 16-bit uInt with a max value of 2048. |
387
|
|
|
* @private |
388
|
|
|
*/ |
389
|
|
|
setRealBits_() { |
390
|
|
|
if (this.bits > 8) { |
391
|
|
|
if (this.bits <= 16) { |
392
|
|
|
this.realBits = 16; |
393
|
|
|
} else if (this.bits <= 24) { |
394
|
|
|
this.realBits = 24; |
395
|
|
|
} else if (this.bits <= 32) { |
396
|
|
|
this.realBits = 32; |
397
|
|
|
} else if (this.bits <= 40) { |
398
|
|
|
this.realBits = 40; |
399
|
|
|
} else if (this.bits <= 48) { |
400
|
|
|
this.realBits = 48; |
401
|
|
|
} else if (this.bits <= 56) { |
402
|
|
|
this.realBits = 56; |
403
|
|
|
} else { |
404
|
|
|
this.realBits = 64; |
405
|
|
|
} |
406
|
|
|
} else { |
407
|
|
|
this.realBits = this.bits; |
408
|
|
|
} |
409
|
|
|
} |
410
|
|
|
|
411
|
|
|
/** |
412
|
|
|
* Set the mask that should be used when writing the last byte of |
413
|
|
|
* data of the type. |
414
|
|
|
* @private |
415
|
|
|
*/ |
416
|
|
|
setLastByteMask_() { |
417
|
|
|
let r = 8 - (this.realBits - this.bits); |
418
|
|
|
this.lastByteMask = Math.pow(2, r > 0 ? r : 8) -1; |
419
|
|
|
} |
420
|
|
|
} |
421
|
|
|
|
422
|
|
|
/** |
423
|
|
|
* Get a binary string representation of a value described as bytes. |
424
|
|
|
* @param {Array<number>|number} bytes The bytes. |
425
|
|
|
* @return {string} |
426
|
|
|
*/ |
427
|
|
|
function getBinary(bytes) { |
428
|
|
|
let binary = ""; |
429
|
|
|
let i = 0; |
430
|
|
|
let bytesLength = bytes.length; |
431
|
|
|
while(i < bytesLength) { |
432
|
|
|
let bits = bytes[i].toString(2); |
433
|
|
|
binary = Array(9 - bits.length).join("0") + bits + binary; |
434
|
|
|
i++; |
435
|
|
|
} |
436
|
|
|
return binary; |
437
|
|
|
} |
438
|
|
|
|
439
|
|
|
/** |
440
|
|
|
* Read a group of bytes by turning it to bits. |
441
|
|
|
* @param {!Array<number>|Uint8Array} bytes An array of bytes. |
442
|
|
|
* @param {number} i The index to read. |
443
|
|
|
* @param {number} numBytes The number of bytes |
444
|
|
|
* (1 for 8-bit, 2 for 16-bit, etc). |
445
|
|
|
* @return {number} |
446
|
|
|
*/ |
447
|
|
|
function readBytesAsBits(bytes, i, numBytes) { |
448
|
|
|
let j = numBytes-1; |
449
|
|
|
let byte = ""; |
450
|
|
|
while (j >= 0) { |
451
|
|
|
let bits = bytes[j + i].toString(2); |
452
|
|
|
byte += Array(9 - bits.length).join("0") + bits; |
453
|
|
|
j--; |
454
|
|
|
} |
455
|
|
|
return parseInt(byte, 2); |
456
|
|
|
} |
457
|
|
|
|
458
|
|
|
module.exports = Type; |
459
|
|
|
|