/* @(#)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/cdefs.h>
__RCSID("$NetBSD: e_fmodl.c,v 1.3 2024/07/17 12:00:48 riastradh Exp $");
#if 0
__FBSDID("$FreeBSD: head/lib/msun/src/e_fmodl.c 181063 2008-07-31 20:09:47Z das $");
#endif

#include "namespace.h"

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

#include "math.h"
#include "math_private.h"
#include <machine/ieee.h>

#ifdef __HAVE_LONG_DOUBLE

#define BIAS (LDBL_MAX_EXP - 1)

#if EXT_FRACLBITS > 32
typedef uint64_t manl_t;
#else
typedef uint32_t manl_t;
#endif

#if EXT_FRACHBITS > 32
typedef uint64_t manh_t;
#else
typedef uint32_t manh_t;
#endif

/*
 * These macros add and remove an explicit integer bit in front of the
 * fractional significand, if the architecture doesn't have such a bit
 * by default already.
 */
#ifdef LDBL_IMPLICIT_NBIT
#define SET_NBIT(hx)    ((hx) | (1ULL << EXT_FRACHBITS))
#define HFRAC_BITS      EXT_FRACHBITS
#define LDBL_NBIT       0
#else
#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 significand fits in a manl_t exactly.
 * - The high part of the significand fits in an int64_t with enough
 *   room for an explicit integer bit in front of the fractional bits.
 */
long double
__ieee754_fmodl(long double x, long double y)
{
        union ieee_ext_u ux = { .extu_ld = x, };
        union ieee_ext_u uy = { .extu_ld = y, };
        int64_t hx,hz;  /* We need a carry bit even if EXT_FRACHBITS is 32. */
        manh_t hy;
        manl_t lx,ly,lz;
        int ix,iy,n,sx;

        sx = ux.extu_sign;

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

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

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

    /* set up {hx,lx}, {hy,ly} and align y to x */
        hx = SET_NBIT(ux.extu_frach);
        hy = SET_NBIT(uy.extu_frach);
        lx = ux.extu_fracl;
        ly = uy.extu_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<(1LL<<HFRAC_BITS)) {   /* normalize x */
            hx = hx+hx+(lx>>MANL_SHIFT); lx = lx+lx;
            iy -= 1;
        }
        ux.extu_frach = hx; /* The significand is truncated here if needed. */
        ux.extu_fracl = lx;
        if (iy < LDBL_MIN_EXP) {
            ux.extu_exp = iy + (BIAS + 512);
            ux.extu_ld *= 0x1p-512;
        } else {
            ux.extu_exp = iy + BIAS;
        }
        x = ux.extu_ld * one;   /* create necessary signal */
        return x;               /* exact output */
}

#endif /* __HAVE_LONG_DOUBLE */