/* @(#)e_fmod.c 1.3 95/01/18 */
/*-
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

#include <sys/types.h>
#include <machine/ieee.h>

#include <float.h>
#include <math.h>
#include <stdint.h>

#include "math_private.h"

#define BIAS (LDBL_MAX_EXP - 1)

/*
 * These macros add and remove an explicit integer bit in front of the
 * fractional mantissa, if the architecture doesn't have such a bit by
 * default already.
 */
#ifdef LDBL_IMPLICIT_NBIT
#define LDBL_NBIT       0
#define SET_NBIT(hx)    ((hx) | (1ULL << LDBL_MANH_SIZE))
#define HFRAC_BITS      EXT_FRACHBITS
#else
#define LDBL_NBIT       0x80000000
#define SET_NBIT(hx)    (hx)
#define HFRAC_BITS      (EXT_FRACHBITS - 1)
#endif

#define MANL_SHIFT      (EXT_FRACLBITS - 1)

static const long double one = 1.0, Zero[] = {0.0, -0.0,};

/*
 * fmodl(x,y)
 * Return x mod y in exact arithmetic
 * Method: shift and subtract
 *
 * Assumptions:
 * - The low part of the mantissa fits in a manl_t exactly.
 * - The high part of the mantissa fits in an int64_t with enough room
 *   for an explicit integer bit in front of the fractional bits.
 */
long double
fmodl(long double x, long double y)
{
        union {
                long double e;
                struct ieee_ext bits;
        } ux, uy;
        int64_t hx,hz;  /* We need a carry bit even if LDBL_MANH_SIZE is 32. */
        uint32_t hy;
        uint32_t lx,ly,lz;
        int ix,iy,n,sx;

        ux.e = x;
        uy.e = y;
        sx = ux.bits.ext_sign;

    /* purge off exception values */
        if((uy.bits.ext_exp|uy.bits.ext_frach|uy.bits.ext_fracl)==0 || /* y=0 */
           (ux.bits.ext_exp == BIAS + LDBL_MAX_EXP) ||   /* or x not finite */
           (uy.bits.ext_exp == BIAS + LDBL_MAX_EXP &&
            ((uy.bits.ext_frach&~LDBL_NBIT)|uy.bits.ext_fracl)!=0)) /* or y is NaN */
            return (x*y)/(x*y);
        if(ux.bits.ext_exp<=uy.bits.ext_exp) {
            if((ux.bits.ext_exp<uy.bits.ext_exp) ||
               (ux.bits.ext_frach<=uy.bits.ext_frach &&
                (ux.bits.ext_frach<uy.bits.ext_frach ||
                 ux.bits.ext_fracl<uy.bits.ext_fracl))) {
                return x;               /* |x|<|y| return x or x-y */
            }
            if(ux.bits.ext_frach==uy.bits.ext_frach &&
                ux.bits.ext_fracl==uy.bits.ext_fracl) {
                return Zero[sx];        /* |x|=|y| return x*0*/
            }
        }

    /* determine ix = ilogb(x) */
        if(ux.bits.ext_exp == 0) {      /* subnormal x */
            ux.e *= 0x1.0p512;
            ix = ux.bits.ext_exp - (BIAS + 512);
        } else {
            ix = ux.bits.ext_exp - BIAS;
        }

    /* determine iy = ilogb(y) */
        if(uy.bits.ext_exp == 0) {      /* subnormal y */
            uy.e *= 0x1.0p512;
            iy = uy.bits.ext_exp - (BIAS + 512);
        } else {
            iy = uy.bits.ext_exp - BIAS;
        }

    /* set up {hx,lx}, {hy,ly} and align y to x */
        hx = SET_NBIT(ux.bits.ext_frach);
        hy = SET_NBIT(uy.bits.ext_frach);
        lx = ux.bits.ext_fracl;
        ly = uy.bits.ext_fracl;

    /* fix point fmod */
        n = ix - iy;

        while(n--) {
            hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
            if(hz<0){hx = hx+hx+(lx>>MANL_SHIFT); lx = lx+lx;}
            else {
                if ((hz|lz)==0)         /* return sign(x)*0 */
                    return Zero[sx];
                hx = hz+hz+(lz>>MANL_SHIFT); lx = lz+lz;
            }
        }
        hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
        if(hz>=0) {hx=hz;lx=lz;}

    /* convert back to floating value and restore the sign */
        if((hx|lx)==0)                  /* return sign(x)*0 */
            return Zero[sx];
        while(hx<(1ULL<<HFRAC_BITS)) {  /* normalize x */
            hx = hx+hx+(lx>>MANL_SHIFT); lx = lx+lx;
            iy -= 1;
        }
        ux.bits.ext_frach = hx; /* The mantissa is truncated here if needed. */
        ux.bits.ext_fracl = lx;
        if (iy < LDBL_MIN_EXP) {
            ux.bits.ext_exp = iy + (BIAS + 512);
            ux.e *= 0x1p-512;
        } else {
            ux.bits.ext_exp = iy + BIAS;
        }
        x = ux.e * one;         /* create necessary signal */
        return x;               /* exact output */
}