209 lines
6.1 KiB
JavaScript
209 lines
6.1 KiB
JavaScript
/**
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* @license Apache-2.0
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*
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* Copyright (c) 2021 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var IS_LITTLE_ENDIAN = require( '@stdlib/assert/is-little-endian' );
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var ArrayBuffer = require( '@stdlib/array/buffer' );
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var DataView = require( '@stdlib/array/dataview' );
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var BigInt = require( '@stdlib/bigint/ctor' );
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var bytesPerElement = require( './../../../base/bytes-per-element' );
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var dtypes = require( './../../../dtypes' ).enum;
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var orders = require( './../../../orders' ).enum;
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var modes = require( './../../../index-modes' ).enum;
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// VARIABLES //
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var DTYPES = dtypes();
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var ORDERS = orders();
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var MODES = modes();
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// MAIN //
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/**
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* Serializes ndarray meta data.
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*
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* ## Notes
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*
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* - This function takes into account ndarray-like objects which may support index modes.
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*
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* - Serialization is performed according to host byte order (endianness).
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*
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* - Meta data format:
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*
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* ```text
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* | endianness (1 byte) | <dtype> (2 bytes) | <ndims> (8 bytes) | <shape> (ndims*8 bytes) | <strides> (ndims*8 bytes) | <offset> (8 bytes) | <order> (1 byte) | <mode> (1 byte) | <nsubmodes> (8 bytes) | <submodes> (nsubmodes*1 bytes) |
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* ```
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*
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* which translates to the following `ArrayBuffer` layout:
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*
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* ```text
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* ArrayBuffer[
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* <endianness>[int8],
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* <dtype>[int16],
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* <ndims>[int64],
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* <shape>[ndims*int64],
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* <strides>[ndims*int64],
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* <offset>[int64],
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* <order>[int8],
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* <mode>[int8],
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* <nsubmodes>[int64],
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* <submodes>[nsubmodes*int8]
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* ]
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* ```
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*
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* where `strides` and `offset` are in units of bytes.
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*
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* - If the endianness is `1`, the byte order is little endian. If the endianness is `0`, the byte order is big endian.
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*
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* - Buffer length:
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*
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* ```text
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* 1 + 2 + 8 + (ndims*8) + (ndims*8) + 8 + 1 + 1 + 8 + (nsubmodes*1) = 29 + (ndims*16) + nsubmodes
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* ```
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*
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* For example, consider a three-dimensional ndarray with one subscript index mode (submode):
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*
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* ```text
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* 29 + (3*16) + 1 = 78 bytes
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* ```
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*
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* - Views:
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*
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* - endianness: `Int8Array( buf, 0, 1 )`
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* - dtype: `Int16Array( buf, 1, 1 )`
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* - ndims: `Int64Array( buf, 3, 1 )`
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* - shape: `Int64Array( buf, 11, ndims )`
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* - strides: `Int64Array( buf, 11+(ndims*8), ndims )`
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* - offset: `Int64Array( buf, 11+(ndims*16), 1 )`
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* - order: `Int8Array( buf, 19+(ndims*16), 1 )`
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* - mode: `Int8Array( buf, 20+(ndims*16), 1 )`
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* - nsubmodes: `Int64Array( buf, 21+(ndims*16), 1 )`
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* - submodes: `Int8Array( buf, 29+(ndims*16), nsubmodes )`
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*
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* @param {ndarrayLike} x - input array
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* @param {string} x.dtype - array data type
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* @param {NonNegativeIntegerArray} x.shape - array shape
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* @param {IntegerArray} x.strides - array strides
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* @param {NonNegativeInteger} x.offset - array index offset
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* @param {string} x.order - array order
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* @param {string} [x.mode='throw'] - array index mode
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* @param {StringArray} [x.submode=[x.mode]] - array subscript index modes
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* @returns {DataView} serialized meta data
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*
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* @example
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* var array = require( '@stdlib/ndarray/array' );
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*
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* var x = array( [ [ 1, 2 ], [ 3, 4 ] ] );
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*
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* var dv = serialize( x );
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* // returns <DataView>
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*/
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function serialize( x ) {
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var nbytes;
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var len;
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var dt;
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var sh;
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var st;
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var sm;
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var v;
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var m;
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var o;
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var s;
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var N;
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var M;
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var i;
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// Check for interface which does the work of serializing to a DataView for us...
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if ( x.__array_meta_dataview__ ) { // eslint-disable-line no-underscore-dangle
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return x.__array_meta_dataview__(); // eslint-disable-line no-underscore-dangle
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}
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// Extract meta data known to be attached to ndarray-like objects:
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dt = x.dtype;
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sh = x.shape;
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st = x.strides;
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N = sh.length; // ndims
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// Extract meta data which may be available on ndarray-like objects (e.g., stdlib ndarray instances):
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m = x.mode || 'throw';
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sm = x.submode || [ m ];
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M = sm.length;
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// Determine number of bytes per element according to the ndarray dtype:
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nbytes = bytesPerElement( dt );
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// Compute the amount of memory we need to allocate for storing meta data:
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len = 29 + (N*16) + M;
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// Allocate raw memory and create a view for interfacing with the allocated memory:
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v = new DataView( new ArrayBuffer( len ) );
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// Endianness: (byteoffset: 0; bytelength: 1)
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o = 0;
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v.setInt8( o, ( IS_LITTLE_ENDIAN ) ? 1 : 0 );
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// Data type: (byteoffset: 1; bytelength: 2)
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o += 1;
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v.setInt16( o, DTYPES[ dt ], IS_LITTLE_ENDIAN );
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// Number of dimensions: (byteoffset: 3; bytelength: 8)
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o += 2;
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v.setBigInt64( o, BigInt( N ), IS_LITTLE_ENDIAN );
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// Shape and strides: (byteoffset: 11 and 11+(ndims*8), respectively; bytelength: ndims*8 for both shape and strides, and, thus, ndims*16 total)
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s = N * 8; // stride length between a dimension (shape[i]) and its associated stride
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o += 8;
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for ( i = 0; i < N; i++ ) {
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v.setBigInt64( o, BigInt( sh[i] ), IS_LITTLE_ENDIAN );
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v.setBigInt64( o+s, BigInt( st[i]*nbytes ), IS_LITTLE_ENDIAN );
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o += 8;
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}
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// Offset: (byteoffset: 11+(ndims*16); bytelength: 8)
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o += s;
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v.setBigInt64( o, BigInt( x.offset*nbytes ), IS_LITTLE_ENDIAN );
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// Order: (byteoffset: 19+(ndims*16); bytelength: 1)
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o += 8;
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v.setInt8( o, ORDERS[ x.order ] );
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// Index mode: (byteoffset: 20+(ndims*16); bytelength: 1)
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o += 1;
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v.setInt8( o, MODES[ m ] );
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// Number of index submodes: (byteoffset: 21+(ndims*16); bytelength: 8)
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o += 1;
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v.setBigInt64( o, BigInt( M ), IS_LITTLE_ENDIAN );
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// Submodes: (byteoffset: 29+(ndims*16); bytelength: nsubmodes*1)
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o += 8;
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for ( i = 0; i < M; i++ ) {
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v.setInt8( o, MODES[ sm[i] ] );
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o += 1;
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}
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return v;
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}
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// EXPORTS //
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module.exports = serialize;
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