fixp-arith.h

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#ifndef _FIXP_ARITH_H
#define _FIXP_ARITH_H

/*
 * Simplistic fixed-point arithmetics.
 * Hmm, I'm probably duplicating some code :(
 *
 * Copyright (c) 2002 Johann Deneux
 */

/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 * Should you need to contact me, the author, you can do so by
 * e-mail - mail your message to <[email protected]>
 */

#include <linux/types.h>

/* The type representing fixed-point values */
typedef s16 fixp_t;

#define FRAC_N 8
#define FRAC_MASK ((1<<FRAC_N)-1)

/* Not to be used directly. Use fixp_{cos,sin} */
static const fixp_t cos_table[46] = {
    0x0100, 0x00FF, 0x00FF, 0x00FE, 0x00FD, 0x00FC, 0x00FA, 0x00F8,
    0x00F6, 0x00F3, 0x00F0, 0x00ED, 0x00E9, 0x00E6, 0x00E2, 0x00DD,
    0x00D9, 0x00D4, 0x00CF, 0x00C9, 0x00C4, 0x00BE, 0x00B8, 0x00B1,
    0x00AB, 0x00A4, 0x009D, 0x0096, 0x008F, 0x0087, 0x0080, 0x0078,
    0x0070, 0x0068, 0x005F, 0x0057, 0x004F, 0x0046, 0x003D, 0x0035,
    0x002C, 0x0023, 0x001A, 0x0011, 0x0008, 0x0000
};


/* a: 123 -> 123.0 */
static inline fixp_t fixp_new(s16 a)
{
    return a<<FRAC_N;
}

/* a: 0xFFFF -> -1.0
      0x8000 -> 1.0
      0x0000 -> 0.0
*/
static inline fixp_t fixp_new16(s16 a)
{
    return ((s32)a)>>(16-FRAC_N);
}

static inline fixp_t fixp_cos(unsigned int degrees)
{
    int quadrant = (degrees / 90) & 3;
    unsigned int i = degrees % 90;

    if (quadrant == 1 || quadrant == 3)
        i = 90 - i;

    i >>= 1;

    return (quadrant == 1 || quadrant == 2)? -cos_table[i] : cos_table[i];
}

static inline fixp_t fixp_sin(unsigned int degrees)
{
    return -fixp_cos(degrees + 90);
}

static inline fixp_t fixp_mult(fixp_t a, fixp_t b)
{
    return ((s32)(a*b))>>FRAC_N;
}

#endif