/**
* @license Apache-2.0
*
* Copyright (c) 2020 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.
*/

#include "stdlib/strided/base/dmskmap.h"
#include <stdint.h>

/**
* Applies a unary function accepting and returning double-precision floating-point numbers to each element in a double-precision floating-point strided input array according to a corresponding element in a strided mask array and assigns each result to an element in a double-precision floating-point strided output array.
*
* @param N           number of indexed elements
* @param X           input array
* @param strideX     X stride length
* @param Mask        mask array
* @param strideMask  Mask stride length
* @param Y           destination array
* @param strideY     Y stride length
* @param fcn         unary function to apply
*
* @example
* #include "stdlib/strided/base/dmskmap.h"
* #include <stdint.h>
*
* static double scale( const double x ) {
*     return x * 10.0;
* }
*
* double X[] = { 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 };
* uint8_t M[] = { 0, 0, 1, 0, 0, 1 };
* double Y[] = { 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 };
*
* int64_t N = 6;
*
* stdlib_strided_dmskmap( N, X, 1, M, 1, Y, 1, scale );
*/
void stdlib_strided_dmskmap( const int64_t N, const double *X, const int64_t strideX, const uint8_t *Mask, const int64_t strideMask, double *Y, const int64_t strideY, double (*fcn)( double ) ) {
	int64_t ix;
	int64_t im;
	int64_t iy;
	int64_t i;
	if ( N <= 0 ) {
		return;
	}
	if ( strideX < 0 ) {
		ix = (1-N) * strideX;
	} else {
		ix = 0;
	}
	if ( strideMask < 0 ) {
		im = (1-N) * strideMask;
	} else {
		im = 0;
	}
	if ( strideY < 0 ) {
		iy = (1-N) * strideY;
	} else {
		iy = 0;
	}
	for ( i = 0; i < N; i++ ) {
		if ( Mask[ im ] == 0 ) {
			Y[ iy ] = fcn( X[ ix ] );
		}
		ix += strideX;
		im += strideMask;
		iy += strideY;
	}
	return;
}