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* @license Apache-2.0
*
* Copyright (c) 2026 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* eslint-disable max-params, max-len */
'use strict';
// MODULES //
var isColumnMajor = require( '@stdlib/ndarray/base/assert/is-column-major' );
// MAIN //
/**
* Returns the index of the first column in a double-precision floating-point input matrix which has the same elements as a provided search vector using alternative indexing semantics.
*
* ## Notes
*
* - If the function is provided an empty matrix or if the function is unable to find a matching column, the function returns `-1` (i.e., an invalid index).
* - The `workspace` array is only applicable when an input matrix is stored in row-major order. When the matrix is stored in column-major order, the workspace array is ignored.
*
* @param {PositiveInteger} M - number of rows in `A`
* @param {PositiveInteger} N - number of columns in `A`
* @param {Float64Array} A - input matrix
* @param {integer} strideA1 - stride of the first dimension of `A`
* @param {integer} strideA2 - stride of the second dimension of `A`
* @param {NonNegativeInteger} offsetA - starting index for `A`
* @param {Float64Array} x - search vector
* @param {integer} strideX - stride length for `x`
* @param {NonNegativeInteger} offsetX - starting index for `x`
* @param {Uint8Array} workspace - workspace array for tracking column match candidates
* @param {integer} strideW - stride length for `workspace`
* @param {NonNegativeInteger} offsetW - starting index for `workspace`
* @returns {integer} column index
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
* var Uint8Array = require( '@stdlib/array/uint8' );
*
* var A = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 0.0, 0.0 ] ); // => [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 0.0, 0.0 ] ]
* var x = new Float64Array( [ 2.0, 4.0, 0.0 ] );
* var workspace = new Uint8Array( 2 );
*
* var out = dindexOfColumn( 3, 2, A, 2, 1, 0, x, 1, 0, workspace, 1, 0 );
* // returns 1
*/
function dindexOfColumn( M, N, A, strideA1, strideA2, offsetA, x, strideX, offsetX, workspace, strideW, offsetW ) {
var da0;
var da1;
var S0;
var S1;
var ia;
var iw;
var ix;
var i0;
var i1;
// Check whether the matrix is an empty matrix...
if ( M <= 0 || N <= 0 ) {
return -1;
}
// Search for the first column matching the search vector...
if ( isColumnMajor( [ strideA1, strideA2 ] ) ) {
S0 = M;
S1 = N;
// Scan a column-major linear buffer from the first indexed element to the last indexed element, always moving in the same direction when both strides are the same sign, thus ensuring cache optimal traversal...
for ( i1 = 0; i1 < S1; i1++ ) {
ia = offsetA + ( i1*strideA2 );
ix = offsetX;
for ( i0 = 0; i0 < S0; i0++ ) {
if ( A[ ia ] !== x[ ix ] ) {
// We found an element which is not in the search vector...
break;
}
ia += strideA1;
ix += strideX;
}
// If we successfully iterated over all rows, then that means we've found a match...
if ( i0 === S0 ) {
return i1;
}
}
// If we've made it here, then no columns match the search vector:
return -1;
}
// Row-major...
S0 = N;
S1 = M;
// Resolve loop offset (pointer) increments:
da0 = strideA2;
da1 = strideA1 - ( S0*strideA2 );
// Initialize the workspace array for tracking which columns contain matching elements:
iw = offsetW;
for ( i0 = 0; i0 < S0; i0++ ) {
workspace[ iw ] = 1;
iw += strideW;
}
// Finding the first matching column when a matrix is stored in row-major order requires effectively performing a full linear scan. In order to ensure cache-efficient traversal, scan across each row (otherwise, if we went column-by-column, we'd hop around linear memory, resulting in poor cache behavior)...
ia = offsetA;
ix = offsetX;
for ( i1 = 0; i1 < S1; i1++ ) {
// Scan across the columns in a row looking for a matching element...
iw = offsetW;
for ( i0 = 0; i0 < S0; i0++ ) {
if ( A[ ia ] !== x[ ix ] ) {
// We found a non-matching element, which means we can exclude this column from the list of column candidates...
workspace[ iw ] = 0;
}
ia += da0;
iw += strideW;
}
ia += da1;
ix += strideX;
}
// Search for the first matching column...
iw = offsetW;
for ( i0 = 0; i0 < S0; i0++ ) {
if ( workspace[ iw ] === 1 ) {
break;
}
iw += strideW;
}
return ( i0 === S0 ) ? -1 : i0;
}
// EXPORTS //
module.exports = dindexOfColumn;
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