/*      $NetBSD: mra.c,v 1.7 2018/03/10 23:25:59 khorben Exp $  */

/*
 * Copyright (c) 1999 Shin Takemura All rights reserved.
 * Copyright (c) 1999 PocketBSD Project. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: mra.c,v 1.7 2018/03/10 23:25:59 khorben Exp $");

#include <sys/param.h>
#include <sys/systm.h>

extern int mra_Y_AX1_BX2_C(const int *, int,
                           const int *, int, const int *, int, int, int,
                           int *, int *, int *);

/*
 * multiple regression analysis
 * Y = AX1 + BX2 + C
 */
int
mra_Y_AX1_BX2_C(const int *y, int ys,
                const int *x1, int x1s, const int *x2, int x2s,
                int n, int scale,
                int *a, int *b, int *c)
{
        int i;
        int64_t X1a, X2a, Ya;
        int64_t X1X1s, X2X2s, X1X2s;
        int64_t YYs, X1Ys, X2Ys;
        int64_t S11, S22, S12;
//      int64_t SYY;
        int64_t S1Y, S2Y;
        int64_t A, B, C, M;
#define AA(p, s, i)     (*((const int *)(((const char *)(p)) + (s) * (i))))
#define X1(i)           AA(x1, x1s, i)
#define X2(i)           AA(x2, x2s, i)
#define Y(i)            AA(y, ys, i)

        /*
         * get average and sum
         */
        X1a = 0;        X2a = 0;        Ya = 0;
        X1X1s = 0;      X2X2s = 0;      X1X2s = 0;
        X1Ys = 0;       X2Ys = 0;       YYs = 0;
        for (i = 0; i < n; i++) {
                X1a += X1(i);
                X2a += X2(i);
                Ya += Y(i);

                X1X1s += X1(i) * X1(i);
                X2X2s += X2(i) * X2(i);
                X1X2s += X1(i) * X2(i);

                X1Ys += X1(i) * Y(i);
                X2Ys += X2(i) * Y(i);
                YYs += Y(i) * Y(i);
        }
        X1a /= n;       X2a /= n;       Ya /= n;

        S11 = X1X1s - n * X1a * X1a;
        S22 = X2X2s - n * X2a * X2a;
        S12 = X1X2s - n * X1a * X2a;

//      SYY = YYs - n * Ya * Ya;
        S1Y = X1Ys - n * X1a * Ya;
        S2Y = X2Ys - n * X2a * Ya;

#if 0
        printf("X1a=%d X2a=%d Ya=%d\n", (int)X1a, (int)X2a, (int)Ya);
        printf("X1X1s=%d X2X2s=%d X1X2s=%d\n", (int)X1X1s, (int)X2X2s, (int)X1X2s);
        printf("X1Ys=%d X2Ys=%d YYs=%d\n", (int)X1Ys, (int)X2Ys, (int)YYs);
        printf("S11=%d S22=%d S12=%d\n", (int)S11, (int)S22, (int)S12);
        printf("SYY=%d S1Y=%d S2Y=%d\n", (int)SYY, (int)S1Y, (int)S2Y);
#endif

        M = (S11 * S22 - S12 * S12);
        if (M == 0) {
                /* error */
                return -1;
        }

        A = (S1Y * S22 - S2Y * S12) * scale / M;
        B = (S2Y * S11 - S1Y * S12) * scale / M;
        C = Ya - (A * X1a + B * X2a) / scale;

#if 0
        printf("A=%d B=%d C=%d\n", (int)A, (int)B, (int)C);
#endif
        *a = A;
        *b = B;
        *c = C;

        return (0);
}