| [6a3a178] | 1 | "use strict";
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| 2 | Object.defineProperty(exports, "__esModule", { value: true });
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| 3 | const { pow, floor } = Math;
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| 4 | const TWO_POW_7 = pow(2, 7);
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| 5 | const TWO_POW_14 = pow(2, 14);
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| 6 | const TWO_POW_21 = pow(2, 21);
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| 7 | const TWO_POW_28 = pow(2, 28);
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| 8 | const TWO_POW_35 = pow(2, 35);
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| 9 | const TWO_POW_42 = pow(2, 42);
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| 10 | const TWO_POW_49 = pow(2, 49);
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| 11 | const TWO_POW_56 = pow(2, 56);
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| 12 | /**
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| 13 | * This class provides encoding and decoding methods for writing and reading
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| 14 | * ZigZag-encoded LEB128-64b9B-variant (Little Endian Base 128) values to/from a
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| 15 | * {@link ByteBuffer}. LEB128's variable length encoding provides for using a
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| 16 | * smaller nuber of bytes for smaller values, and the use of ZigZag encoding
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| 17 | * allows small (closer to zero) negative values to use fewer bytes. Details
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| 18 | * on both LEB128 and ZigZag can be readily found elsewhere.
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| 19 | *
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| 20 | * The LEB128-64b9B-variant encoding used here diverges from the "original"
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| 21 | * LEB128 as it extends to 64 bit values: In the original LEB128, a 64 bit
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| 22 | * value can take up to 10 bytes in the stream, where this variant's encoding
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| 23 | * of a 64 bit values will max out at 9 bytes.
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| 24 | *
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| 25 | * As such, this encoder/decoder should NOT be used for encoding or decoding
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| 26 | * "standard" LEB128 formats (e.g. Google Protocol Buffers).
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| 27 | */
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| 28 | class ZigZagEncoding {
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| 29 | /**
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| 30 | * Writes a long value to the given buffer in LEB128 ZigZag encoded format
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| 31 | * (negative numbers not supported)
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| 32 | * @param buffer the buffer to write to
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| 33 | * @param value the value to write to the buffer
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| 34 | */
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| 35 | static encode(buffer, value) {
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| 36 | if (value >= 0) {
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| 37 | value = value * 2;
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| 38 | }
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| 39 | else {
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| 40 | value = -value * 2 - 1;
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| 41 | }
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| 42 | if (value < TWO_POW_7) {
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| 43 | buffer.put(value);
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| 44 | }
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| 45 | else {
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| 46 | buffer.put(value | 0x80);
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| 47 | if (value < TWO_POW_14) {
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| 48 | buffer.put(floor(value / TWO_POW_7));
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| 49 | }
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| 50 | else {
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| 51 | buffer.put(floor(value / TWO_POW_7) | 0x80);
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| 52 | if (value < TWO_POW_21) {
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| 53 | buffer.put(floor(value / TWO_POW_14));
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| 54 | }
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| 55 | else {
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| 56 | buffer.put(floor(value / TWO_POW_14) | 0x80);
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| 57 | if (value < TWO_POW_28) {
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| 58 | buffer.put(floor(value / TWO_POW_21));
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| 59 | }
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| 60 | else {
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| 61 | buffer.put(floor(value / TWO_POW_21) | 0x80);
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| 62 | if (value < TWO_POW_35) {
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| 63 | buffer.put(floor(value / TWO_POW_28));
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| 64 | }
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| 65 | else {
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| 66 | buffer.put(floor(value / TWO_POW_28) | 0x80);
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| 67 | if (value < TWO_POW_42) {
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| 68 | buffer.put(floor(value / TWO_POW_35));
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| 69 | }
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| 70 | else {
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| 71 | buffer.put(floor(value / TWO_POW_35) | 0x80);
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| 72 | if (value < TWO_POW_49) {
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| 73 | buffer.put(floor(value / TWO_POW_42));
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| 74 | }
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| 75 | else {
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| 76 | buffer.put(floor(value / TWO_POW_42) | 0x80);
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| 77 | if (value < TWO_POW_56) {
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| 78 | buffer.put(floor(value / TWO_POW_49));
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| 79 | }
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| 80 | else {
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| 81 | // should not happen
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| 82 | buffer.put(floor(value / TWO_POW_49) + 0x80);
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| 83 | buffer.put(floor(value / TWO_POW_56));
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| 84 | }
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| 85 | }
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| 86 | }
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| 87 | }
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| 88 | }
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| 89 | }
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| 90 | }
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| 91 | }
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| 92 | }
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| 93 | /**
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| 94 | * Read an LEB128-64b9B ZigZag encoded long value from the given buffer
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| 95 | * (negative numbers not supported)
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| 96 | * @param buffer the buffer to read from
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| 97 | * @return the value read from the buffer
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| 98 | */
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| 99 | static decode(buffer) {
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| 100 | let v = buffer.get();
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| 101 | let value = v & 0x7f;
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| 102 | if ((v & 0x80) != 0) {
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| 103 | v = buffer.get();
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| 104 | value += (v & 0x7f) * TWO_POW_7;
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| 105 | if ((v & 0x80) != 0) {
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| 106 | v = buffer.get();
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| 107 | value += (v & 0x7f) * TWO_POW_14;
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| 108 | if ((v & 0x80) != 0) {
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| 109 | v = buffer.get();
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| 110 | value += (v & 0x7f) * TWO_POW_21;
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| 111 | if ((v & 0x80) != 0) {
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| 112 | v = buffer.get();
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| 113 | value += (v & 0x7f) * TWO_POW_28;
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| 114 | if ((v & 0x80) != 0) {
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| 115 | v = buffer.get();
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| 116 | value += (v & 0x7f) * TWO_POW_35;
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| 117 | if ((v & 0x80) != 0) {
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| 118 | v = buffer.get();
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| 119 | value += (v & 0x7f) * TWO_POW_42;
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| 120 | if ((v & 0x80) != 0) {
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| 121 | v = buffer.get();
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| 122 | value += (v & 0x7f) * TWO_POW_49;
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| 123 | if ((v & 0x80) != 0) {
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| 124 | v = buffer.get();
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| 125 | value += (v & 0x7f) * TWO_POW_56;
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| 126 | }
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| 127 | }
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| 128 | }
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| 129 | }
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| 130 | }
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| 131 | }
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| 132 | }
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| 133 | }
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| 134 | if (value % 2 === 0) {
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| 135 | value = value / 2;
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| 136 | }
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| 137 | else {
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| 138 | value = -(value + 1) / 2;
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| 139 | }
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| 140 | return value;
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| 141 | }
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| 142 | }
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| 143 | exports.default = ZigZagEncoding;
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| 144 | //# sourceMappingURL=ZigZagEncoding.js.map |
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