mirror of
https://gitlab.com/wgp/dougal/software.git
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1cb9d4b1e2
It encodes / decodes sequence / preplot data using an efficient binary format for sending large amounts of data across the wire and for (relatively) memory efficient client-side use.
140 lines
3.5 KiB
JavaScript
140 lines
3.5 KiB
JavaScript
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/** Binary encoder
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*
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* This module encodes scalar data from a grid-like source
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* into a packed binary format for bandwidth efficiency and
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* speed of access.
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*
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* Data are indexed by i & j values, with "i" being constant
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* (e.g., a sequence or line number) and "j" expected to change
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* by a constant, linear amount (e.g., point numbers). All data
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* from consecutive "j" values will be encoded as a single array
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* (or series of arrays if multiple values are encoded).
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* If there is a jump in the "j" progression, a new "chunk" will
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* be started with a new array (or series of arrays).
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*
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* Multiple values may be encoded per (i, j) pair, using any of
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* the types supported by JavaScript's TypedArray except for
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* Float16 and Uint8Clamped. Each variable can be encoded with
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* a different size.
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*
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* Values may be encoded directly or as deltas from an initial
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* value. The latter is particularly efficient when dealing with
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* monotonically incrementing data, such as timestamps.
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*
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* The conceptual packet format for sequentially encoded data
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* looks like this:
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*
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* <msg-type> <count: x> <i> <j0> <Δj>
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*
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* <Δelement_count: y>
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* <element_count: z>
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*
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* <Δelement_1_type_base> … <Δelement_y_type_base>
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* <Δelement_1_type_incr> … <Δelement_y_type_incr>
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* <elem_1_type> … <elem_z_type>
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*
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* <Δelement_1_first> … <Δelement_z_first>
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*
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* <Δelem_1_0> … <Δelem_1_x>
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* …
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* <Δelem_y_0> … <Δelem_y_x>
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* <elem_1_0> … <elem_1_x>
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* …
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* <elem_z_0> … <elem_z_x>
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*
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*
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* The conceptual packet format for interleaved encoded data
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* looks like this:
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*
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*
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* <msg-type> <count: x> <i> <j0> <Δj>
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*
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* <Δelement_count: y>
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* <element_count: z>
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*
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* <Δelement_1_type_base> … <Δelement_y_type_base>
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* <Δelement_1_type_incr> … <Δelement_y_type_incr>
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* <elem_1_type> … <elem_z_type>
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*
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* <Δelement_1_first> … <Δelement_y_first>
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*
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* <Δelem_1_0> <Δelem_2_0> … <Δelem_y_0> <elem_1_0> <elem_2_0> … <elem_z_0>
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* <Δelem_1_1> <Δelem_2_1> … <Δelem_y_1> <elem_1_1> <elem_2_1> … <elem_z_1>
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* …
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* <Δelem_1_x> <Δelem_2_x> … <Δelem_y_x> <elem_1_x> <elem_2_x> … <elem_z_x>
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*
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*
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* Usage example:
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*
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* json = [
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* {
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* sequence: 7,
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* sailline: 5354,
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* line: 5356,
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* point: 1068,
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* tstamp: 1695448704372,
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* objrefraw: 3,
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* objreffinal: 4
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* },
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* {
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* sequence: 7,
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* sailline: 5354,
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* line: 5352,
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* point: 1070,
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* tstamp: 1695448693612,
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* objrefraw: 2,
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* objreffinal: 3
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* },
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* {
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* sequence: 7,
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* sailline: 5354,
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* line: 5356,
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* point: 1072,
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* tstamp: 1695448684624,
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* objrefraw: 3,
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* objreffinal: 4
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* }
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* ];
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*
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* deltas = [
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* { key: el => el.tstamp, baseType: BigUint64Array, incrType: Int16Array }
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* ];
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*
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* elems = [
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* { key: el => el.objrefraw, type: Uint8Array },
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* { key: el => el.objreffinal, type: Uint8Array }
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* ];
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*
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* i = el => el.sequence;
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*
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* j = el => el.point;
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*
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* bundle = encode(json, i, j, deltas, elems);
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*
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* // bundle:
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*
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* Uint8Array(40) [
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* 36, 0, 0, 28, 17, 0, 3, 0, 7, 0,
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* 44, 4, 2, 0, 1, 2, 42, 1, 1, 116,
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* 37, 158, 192, 138, 1, 0, 0, 0, 0, 0,
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* 248, 213, 228, 220, 3, 2, 3, 4, 3, 4
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* ]
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*
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* decode(bundle);
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*
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* {
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* i: 7,
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* j: [ 1068, 1070, 1072 ],
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* 'Δelems': [ [ 1695448704372, 1695448693612, 1695448684624 ] ],
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* elems: [ [ 3, 2, 3 ], [ 4, 3, 4 ] ]
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* }
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*
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*/
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module.exports = {
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encode: {...require('./encode')},
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decode: {...require('./decode')},
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...require('./classes')
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};
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