Exemple #1
0
GEN
addrr_sign(GEN x, long sx, GEN y, long sy)
{
  long lx, ex = expo(x);
  long ly, ey = expo(y), e = ey - ex;
  long i, j, lz, ez, m;
  int extend, f2;
  GEN z;
  LOCAL_OVERFLOW;

  if (!sy)
  {
    if (!sx)
    {
      if (e > 0) ex = ey;
      return real_0_bit(ex);
    }
    if (e >= 0) return real_0_bit(ey);
    lz = nbits2prec(-e);
    lx = lg(x); if (lz > lx) lz = lx;
    z = cgetr(lz); while(--lz) z[lz] = x[lz];
    setsigne(z,sx); return z;
  }
  if (!sx)
  {
    if (e <= 0) return real_0_bit(ex);
    lz = nbits2prec(e);
    ly = lg(y); if (lz > ly) lz = ly;
    z = cgetr(lz); while (--lz) z[lz] = y[lz];
    setsigne(z,sy); return z;
  }

  if (e < 0) { swap(x,y); lswap(sx,sy); ey=ex; e=-e; }
  /* now ey >= ex */
  lx = lg(x);
  ly = lg(y);
  /* If exponents differ, need to shift one argument, here x. If
   * extend = 1: extension of x,z by m < BIL bits (round to 1 word) */
  /* in this case, lz = lx + d + 1, otherwise lx + d */
  extend = 0;
  if (e)
  {
    long d = dvmdsBIL(e, &m), l = ly-d;
    if (l <= 2) return rcopy_sign(y, sy);
    if (l > lx) { lz = lx + d + 1; extend = 1; }
    else        { lz = ly; lx = l; }
    if (m)
    { /* shift x right m bits */
      const pari_sp av = avma;
      const ulong sh = BITS_IN_LONG-m;
      GEN p1 = x; x = new_chunk(lx + lz + 1);
      shift_right(x,p1,2,lx, 0,m);
      if (extend) uel(x,lx) = uel(p1,lx-1) << sh;
      avma = av; /* HACK: cgetr(lz) will not overwrite x */
    }
  }
  else
  { /* d = 0 */
    m = 0;
    if (lx > ly) lx = ly;
    lz = lx;
  }

  if (sx == sy)
  { /* addition */
    i = lz-1;
    j = lx-1;
    if (extend) {
      ulong garde = addll(x[lx], y[i]);
      if (m < 4) /* don't extend for few correct bits */
        z = cgetr(--lz);
      else
      {
        z = cgetr(lz);
        z[i] = garde;
      }
    }
    else
    {
      z = cgetr(lz);
      z[i] = addll(x[j], y[i]); j--;
    }
    i--;
    for (; j>=2; i--,j--) z[i] = addllx(x[j],y[i]);
    if (overflow)
    {
      z[1] = 1; /* stops since z[1] != 0 */
      for (;;) { z[i] = uel(y,i)+1; if (z[i--]) break; }
      if (i <= 0)
      {
        shift_right(z,z, 2,lz, 1,1);
        z[1] = evalsigne(sx) | evalexpo(ey+1); return z;
      }
    }
    for (; i>=2; i--) z[i] = y[i];
    z[1] = evalsigne(sx) | evalexpo(ey); return z;
  }

  /* subtraction */
  if (e) f2 = 1;
  else
  {
    i = 2; while (i < lx && x[i] == y[i]) i++;
    if (i==lx) return real_0_bit(ey+1 - prec2nbits(lx));
    f2 = (uel(y,i) > uel(x,i));
  }
  /* result is non-zero. f2 = (y > x) */
  i = lz-1; z = cgetr(lz);
  if (f2)
  {
    j = lx-1;
    if (extend) z[i] = subll(y[i], x[lx]);
    else        z[i] = subll(y[i], x[j--]);
    for (i--; j>=2; i--) z[i] = subllx(y[i], x[j--]);
    if (overflow) /* stops since y[1] != 0 */
      for (;;) { z[i] = uel(y,i)-1; if (y[i--]) break; }
    for (; i>=2; i--) z[i] = y[i];
    sx = sy;
  }
  else
  {
    if (extend) z[i] = subll(x[lx], y[i]);
    else        z[i] = subll(x[i],  y[i]);
    for (i--; i>=2; i--) z[i] = subllx(x[i], y[i]);
  }

  x = z+2; i = 0; while (!x[i]) i++;
  lz -= i; z += i;
  j = bfffo(z[2]); /* need to shift left by j bits to normalize mantissa */
  ez = ey - (j | (i * BITS_IN_LONG));
  if (extend)
  { /* z was extended by d+1 words [should be e bits = d words + m bits] */
    /* not worth keeping extra word if less than 5 significant bits in there */
    if (m - j < 5 && lz > 3)
    { /* shorten z */
      ulong last = (ulong)z[--lz]; /* cancelled word */

      /* if we need to shift anyway, shorten from left
       * If not, shorten from right, neutralizing last word of z */
      if (j == 0)
        /* stackdummy((pari_sp)(z + lz+1), (pari_sp)(z + lz)); */
        z[lz] = evaltyp(t_VECSMALL) | _evallg(1);
      else
      {
        GEN t = z;
        z++; shift_left(z,t,2,lz-1, last,j);
      }
      if ((last<<j) & HIGHBIT)
      { /* round up */
        i = lz-1;
        while (++((ulong*)z)[i] == 0 && i > 1) i--;
        if (i == 1) { ez++; z[2] = (long)HIGHBIT; }
      }
    }
    else if (j) shift_left(z,z,2,lz-1, 0,j);
  }
  else if (j) shift_left(z,z,2,lz-1, 0,j);
  z[1] = evalsigne(sx) | evalexpo(ez);
  z[0] = evaltyp(t_REAL) | evallg(lz);
  avma = (pari_sp)z; return z;
}
Exemple #2
0
static GEN
real_0_digits(long n) {
  long b = (n > 0)? (long)(n/LOG10_2): (long)-((-n)/LOG10_2 + 1);
  return real_0_bit(b);
}