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