dtoa.cpp

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        word0(d) &= ~Sign_bit;    /* clear sign bit */
    } else
        *sign = 0;

    if ((word0(d) & Exp_mask) == Exp_mask)
    {
        /* Infinity or NaN */
        *decpt = 9999;
        if (!word1(d) && !(word0(d) & 0xfffff))
            return nrv_alloc("Infinity", rve, 8);
        return nrv_alloc("NaN", rve, 3);
    }
    if (!dval(d)) {
        *decpt = 1;
        return nrv_alloc("0", rve, 1);
    }

#ifdef SET_INEXACT
    try_quick = oldinexact = get_inexact();
    inexact = 1;
#endif

    b = d2b(dval(d), &be, &bbits);
#ifdef Sudden_Underflow
    i = (int)(word0(d) >> Exp_shift1 & (Exp_mask >> Exp_shift1));
#else
    if ((i = (int)(word0(d) >> Exp_shift1 & (Exp_mask >> Exp_shift1)))) {
#endif
        dval(d2) = dval(d);
        word0(d2) &= Frac_mask1;
        word0(d2) |= Exp_11;

        /* log(x)    ~=~ log(1.5) + (x-1.5)/1.5
         * log10(x)     =  log(x) / log(10)
         *        ~=~ log(1.5)/log(10) + (x-1.5)/(1.5*log(10))
         * log10(d) = (i-Bias)*log(2)/log(10) + log10(d2)
         *
         * This suggests computing an approximation k to log10(d) by
         *
         * k = (i - Bias)*0.301029995663981
         *    + ( (d2-1.5)*0.289529654602168 + 0.176091259055681 );
         *
         * We want k to be too large rather than too small.
         * The error in the first-order Taylor series approximation
         * is in our favor, so we just round up the constant enough
         * to compensate for any error in the multiplication of
         * (i - Bias) by 0.301029995663981; since |i - Bias| <= 1077,
         * and 1077 * 0.30103 * 2^-52 ~=~ 7.2e-14,
         * adding 1e-13 to the constant term more than suffices.
         * Hence we adjust the constant term to 0.1760912590558.
         * (We could get a more accurate k by invoking log10,
         *  but this is probably not worthwhile.)
         */

        i -= Bias;
#ifndef Sudden_Underflow
        denorm = 0;
    } else {
        /* d is denormalized */

        i = bbits + be + (Bias + (P - 1) - 1);
        x = i > 32  ? word0(d) << 64 - i | word1(d) >> i - 32
                : word1(d) << 32 - i;
        dval(d2) = x;
        word0(d2) -= 31 * Exp_msk1; /* adjust exponent */
        i -= (Bias + (P - 1) - 1) + 1;
        denorm = 1;
    }
#endif
    ds = (dval(d2) - 1.5) * 0.289529654602168 + 0.1760912590558 + (i * 0.301029995663981);
    k = (int)ds;
    if (ds < 0. && ds != k)
        k--;    /* want k = floor(ds) */
    k_check = 1;
    if (k >= 0 && k <= Ten_pmax) {
        if (dval(d) < tens[k])
            k--;
        k_check = 0;
    }
    j = bbits - i - 1;
    if (j >= 0) {
        b2 = 0;
        s2 = j;
    } else {
        b2 = -j;
        s2 = 0;
    }
    if (k >= 0) {
        b5 = 0;
        s5 = k;
        s2 += k;
    } else {
        b2 -= k;
        b5 = -k;
        s5 = 0;
    }

#ifndef SET_INEXACT
#ifdef Check_FLT_ROUNDS
    try_quick = Rounding == 1;
#else
    try_quick = 1;
#endif
#endif /*SET_INEXACT*/

    leftright = 1;
    ilim = ilim1 = -1;
    i = 18;
    ndigits = 0;
    s = s0 = rv_alloc(i);

    if (ilim >= 0 && ilim <= Quick_max && try_quick) {

        /* Try to get by with floating-point arithmetic. */

        i = 0;
        dval(d2) = dval(d);
        k0 = k;
        ilim0 = ilim;
        ieps = 2; /* conservative */
        if (k > 0) {
            ds = tens[k & 0xf];
            j = k >> 4;
            if (j & Bletch) {
                /* prevent overflows */
                j &= Bletch - 1;
                dval(d) /= bigtens[n_bigtens - 1];
                ieps++;
            }
            for (; j; j >>= 1, i++) {
                if (j & 1) {
                    ieps++;
                    ds *= bigtens[i];
                }
            }
            dval(d) /= ds;
        } else if ((j1 = -k)) {
            dval(d) *= tens[j1 & 0xf];
            for (j = j1 >> 4; j; j >>= 1, i++) {
                if (j & 1) {
                    ieps++;
                    dval(d) *= bigtens[i];
                }
            }
        }
        if (k_check && dval(d) < 1. && ilim > 0) {
            if (ilim1 <= 0)
                goto fast_failed;
            ilim = ilim1;
            k--;
            dval(d) *= 10.;
            ieps++;
        }
        dval(eps) = (ieps * dval(d)) + 7.;
        word0(eps) -= (P - 1) * Exp_msk1;
        if (ilim == 0) {
            S = mhi = 0;
            dval(d) -= 5.;
            if (dval(d) > dval(eps))
                goto one_digit;
            if (dval(d) < -dval(eps))
                goto no_digits;
            goto fast_failed;
        }
#ifndef No_leftright
        if (leftright) {
            /* Use Steele & White method of only
             * generating digits needed.
             */
            dval(eps) = (0.5 / tens[ilim - 1]) - dval(eps);
            for (i = 0;;) {
                L = (long int)dval(d);
                dval(d) -= L;
                *s++ = '0' + (int)L;
                if (dval(d) < dval(eps))
                    goto ret1;
                if (1. - dval(d) < dval(eps))
                    goto bump_up;
                if (++i >= ilim)
                    break;
                dval(eps) *= 10.;
                dval(d) *= 10.;
            }
        } else {
#endif
            /* Generate ilim digits, then fix them up. */
            dval(eps) *= tens[ilim - 1];
            for (i = 1;; i++, dval(d) *= 10.) {
                L = (int32_t)(dval(d));
                if (!(dval(d) -= L))
                    ilim = i;
                *s++ = '0' + (int)L;
                if (i == ilim) {
                    if (dval(d) > 0.5 + dval(eps))
                        goto bump_up;
                    else if (dval(d) < 0.5 - dval(eps)) {
                        while (*--s == '0') { }
                        s++;
                        goto ret1;
                    }
                    break;
                }
            }
#ifndef No_leftright
        }
#endif
fast_failed:
        s = s0;
        dval(d) = dval(d2);
        k = k0;
        ilim = ilim0;
    }

    /* Do we have a "small" integer? */

    if (be >= 0 && k <= Int_max) {
        /* Yes. */
        ds = tens[k];
        if (ndigits < 0 && ilim <= 0) {
            S = mhi = 0;
            if (ilim < 0 || dval(d) <= 5 * ds)
                goto no_digits;
            goto one_digit;
        }
        for (i = 1;; i++, dval(d) *= 10.) {
            L = (int32_t)(dval(d) / ds);
            dval(d) -= L * ds;
#ifdef Check_FLT_ROUNDS
            /* If FLT_ROUNDS == 2, L will usually be high by 1 */
            if (dval(d) < 0) {
                L--;
                dval(d) += ds;
            }
#endif
            *s++ = '0' + (int)L;
            if (!dval(d)) {
#ifdef SET_INEXACT
                inexact = 0;
#endif
                break;
            }
            if (i == ilim) {
                dval(d) += dval(d);
                if (dval(d) > ds || dval(d) == ds && L & 1) {
bump_up:
                    while (*--s == '9')
                        if (s == s0) {
                            k++;
                            *s = '0';
                            break;
                        }
                    ++*s++;
                }
                break;
            }
        }
        goto ret1;
    }

    m2 = b2;
    m5 = b5;
    mhi = mlo = 0;
    if (leftright) {
        i =
#ifndef Sudden_Underflow
            denorm ? be + (Bias + (P - 1) - 1 + 1) :
#endif
            1 + P - bbits;
        b2 += i;
        s2 += i;
        mhi = i2b(1);
    }
    if (m2 > 0 && s2 > 0) {
        i = m2 < s2 ? m2 : s2;
        b2 -= i;
        m2 -= i;
        s2 -= i;
    }
    if (b5 > 0) {
        if (leftright) {
            if (m5 > 0) {
                mhi = pow5mult(mhi, m5);
                b1 = mult(mhi, b);
                Bfree(b);
                b = b1;
            }
            if ((j = b5 - m5))
                b = pow5mult(b, j);
        } else
            b = pow5mult(b, b5);
        }
    S = i2b(1);
    if (s5 > 0)
        S = pow5mult(S, s5);

    /* Check for special case that d is a normalized power of 2. */

    spec_case = 0;
    if (!word1(d) && !(word0(d) & Bndry_mask)
#ifndef Sudden_Underflow
     && word0(d) & (Exp_mask & ~Exp_msk1)
#endif
            ) {
        /* The special case */
        b2 += Log2P;
        s2 += Log2P;
        spec_case = 1;
    }

    /* Arrange for convenient computation of quotients:
     * shift left if necessary so divisor has 4 leading 0 bits.
     *
     * Perhaps we should just compute leading 28 bits of S once
     * and for all and pass them and a shift to quorem, so it
     * can do shifts and ors to compute the numerator for q.
     */
#ifdef Pack_32
    if ((i = ((s5 ? 32 - hi0bits(S->x[S->wds - 1]) : 1) + s2) & 0x1f))
        i = 32 - i;
#else
    if ((i = ((s5 ? 32 - hi0bits(S->x[S->wds - 1]) : 1) + s2) & 0xf))
        i = 16 - i;
#endif
    if (i > 4) {
        i -= 4;
        b2 += i;
        m2 += i;
        s2 += i;
    } else if (i < 4) {
        i += 28;
        b2 += i;
        m2 += i;
        s2 += i;
    }
    if (b2 > 0)
        b = lshift(b, b2);
    if (s2 > 0)
        S = lshift(S, s2);
    if (k_check) {
        if (cmp(b,S) < 0) {
            k--;
            b = multadd(b, 10, 0);    /* we botched the k estimate */
            if (leftright)
                mhi = multadd(mhi, 10, 0);
            ilim = ilim1;
        }
    }

    if (leftright) {
        if (m2 > 0)
            mhi = lshift(mhi, m2);

        /* Compute mlo -- check for special case
         * that d is a normalized power of 2.
         */

        mlo = mhi;
        if (spec_case) {
            mhi = Balloc(mhi->k);
            Bcopy(mhi, mlo);
            mhi = lshift(mhi, Log2P);
        }

        for (i = 1;;i++) {
            dig = quorem(b,S) + '0';
            /* Do we yet have the shortest decimal string
             * that will round to d?
             */
            j = cmp(b, mlo);
            delta = diff(S, mhi);
            j1 = delta->sign ? 1 : cmp(b, delta);
            Bfree(delta);
            if (j1 == 0 && !(word1(d) & 1)) {
                if (dig == '9')
                    goto round_9_up;
                if (j > 0)
                    dig++;
#ifdef SET_INEXACT
                else if (!b->x[0] && b->wds <= 1)
                    inexact = 0;
#endif
                *s++ = dig;
                goto ret;
            }
            if (j < 0 || j == 0 && !(word1(d) & 1)) {
                if (!b->x[0] && b->wds <= 1) {
#ifdef SET_INEXACT
                    inexact = 0;
#endif
                    goto accept_dig;
                }
                if (j1 > 0) {
                    b = lshift(b, 1);
                    j1 = cmp(b, S);
                    if ((j1 > 0 || j1 == 0 && dig & 1) && dig++ == '9')
                        goto round_9_up;
                }
accept_dig:
                *s++ = dig;
                goto ret;
            }
            if (j1 > 0) {
                if (dig == '9') { /* possible if i == 1 */
round_9_up:
                    *s++ = '9';
                    goto roundoff;
                }
                *s++ = dig + 1;
                goto ret;
            }
            *s++ = dig;
            if (i == ilim)
                break;
            b = multadd(b, 10, 0);
            if (mlo == mhi)
                mlo = mhi = multadd(mhi, 10, 0);
            else {
                mlo = multadd(mlo, 10, 0);
                mhi = multadd(mhi, 10, 0);
            }
        }
    } else
        for (i = 1;; i++) {
            *s++ = dig = quorem(b,S) + '0';
            if (!b->x[0] && b->wds <= 1) {
#ifdef SET_INEXACT
                inexact = 0;
#endif
                goto ret;
            }
            if (i >= ilim)
                break;
            b = multadd(b, 10, 0);
        }

    /* Round off last digit */

    b = lshift(b, 1);
    j = cmp(b, S);
    if (j > 0 || j == 0 && dig & 1) {
roundoff:
        while (*--s == '9')
            if (s == s0) {
                k++;
                *s++ = '1';
                goto ret;
            }
        ++*s++;
    } else {
        while (*--s == '0') { }
        s++;
    }
    goto ret;
no_digits:
    k = -1 - ndigits;
    goto ret;
one_digit:
    *s++ = '1';
    k++;
    goto ret;
ret:
    Bfree(S);
    if (mhi) {
        if (mlo && mlo != mhi)
            Bfree(mlo);
        Bfree(mhi);
    }
ret1:
#ifdef SET_INEXACT
    if (inexact) {
        if (!oldinexact) {
            word0(d) = Exp_1 + (70 << Exp_shift);
            word1(d) = 0;
            dval(d) += 1.;
        }
    } else if (!oldinexact)
        clear_inexact();
#endif
    Bfree(b);
    *s = 0;
    *decpt = k + 1;
    if (rve)
        *rve = s;
    return s0;
}

} // namespace WTF