dtoa.java

java中比较著名的js引擎当属mozilla开源的rhino

            if (idx < S_bytes.length)
                S_hiWord |= (S_bytes[idx] & 0xFF);
        }
        if ((i = (((s5 != 0) ? 32 - hi0bits(S_hiWord) : 1) + s2) & 0x1f) != 0)
            i = 32 - i;
        /* i is the number of leading zero bits in the most significant word of S*2^s2. */
        if (i > 4) {
            i -= 4;
            b2 += i;
            m2 += i;
            s2 += i;
        }
        else if (i < 4) {
            i += 28;
            b2 += i;
            m2 += i;
            s2 += i;
        }
        /* Now S*2^s2 has exactly four leading zero bits in its most significant word. */
        if (b2 > 0)
            b = b.shiftLeft(b2);
        if (s2 > 0)
            S = S.shiftLeft(s2);
        /* Now we have d/10^k = b/S and
           (mhi * 2^m2) / S = maximum acceptable error, divided by 10^k. */
        if (k_check) {
            if (b.compareTo(S) < 0) {
                k--;
                b = b.multiply(BigInteger.valueOf(10));  /* we botched the k estimate */
                if (leftright)
                    mhi = mhi.multiply(BigInteger.valueOf(10));
                ilim = ilim1;
            }
        }
        /* At this point 1 <= d/10^k = b/S < 10. */

        if (ilim <= 0 && mode > 2) {
            /* We're doing fixed-mode output and d is less than the minimum nonzero output in this mode.
               Output either zero or the minimum nonzero output depending on which is closer to d. */
            if ((ilim < 0 )
                    || ((i = b.compareTo(S = S.multiply(BigInteger.valueOf(5)))) < 0)
                    || ((i == 0 && !biasUp))) {
            /* Always emit at least one digit.  If the number appears to be zero
               using the current mode, then emit one '0' digit and set decpt to 1. */
            /*no_digits:
                k = -1 - ndigits;
                goto ret; */
                buf.setLength(0);
                buf.append('0');        /* copy "0" to buffer */
                return 1;
//                goto no_digits;
            }
//        one_digit:
            buf.append('1');
            k++;
            return k + 1;
        }
        if (leftright) {
            if (m2 > 0)
                mhi = mhi.shiftLeft(m2);

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

            mlo = mhi;
            if (spec_case) {
                mhi = mlo;
                mhi = mhi.shiftLeft(Log2P);
            }
            /* mlo/S = maximum acceptable error, divided by 10^k, if the output is less than d. */
            /* mhi/S = maximum acceptable error, divided by 10^k, if the output is greater than d. */

            for(i = 1;;i++) {
                BigInteger[] divResult = b.divideAndRemainder(S);
                b = divResult[1];
                dig = (char)(divResult[0].intValue() + '0');
                /* Do we yet have the shortest decimal string
                 * that will round to d?
                 */
                j = b.compareTo(mlo);
                /* j is b/S compared with mlo/S. */
                delta = S.subtract(mhi);
                j1 = (delta.signum() <= 0) ? 1 : b.compareTo(delta);
                /* j1 is b/S compared with 1 - mhi/S. */
                if ((j1 == 0) && (mode == 0) && ((word1(d) & 1) == 0)) {
                    if (dig == '9') {
                        buf.append('9');
                        if (roundOff(buf)) {
                            k++;
                            buf.append('1');
                        }
                        return k + 1;
//                        goto round_9_up;
                    }
                    if (j > 0)
                        dig++;
                    buf.append(dig);
                    return k + 1;
                }
                if ((j < 0)
                        || ((j == 0)
                            && (mode == 0)
                            && ((word1(d) & 1) == 0)
                    )) {
                    if (j1 > 0) {
                        /* Either dig or dig+1 would work here as the least significant decimal digit.
                           Use whichever would produce a decimal value closer to d. */
                        b = b.shiftLeft(1);
                        j1 = b.compareTo(S);
                        if (((j1 > 0) || (j1 == 0 && (((dig & 1) == 1) || biasUp)))
                            && (dig++ == '9')) {
                                buf.append('9');
                                if (roundOff(buf)) {
                                    k++;
                                    buf.append('1');
                                }
                                return k + 1;
//                                goto round_9_up;
                        }
                    }
                    buf.append(dig);
                    return k + 1;
                }
                if (j1 > 0) {
                    if (dig == '9') { /* possible if i == 1 */
//                    round_9_up:
//                        *s++ = '9';
//                        goto roundoff;
                        buf.append('9');
                        if (roundOff(buf)) {
                            k++;
                            buf.append('1');
                        }
                        return k + 1;
                    }
                    buf.append((char)(dig + 1));
                    return k + 1;
                }
                buf.append(dig);
                if (i == ilim)
                    break;
                b = b.multiply(BigInteger.valueOf(10));
                if (mlo == mhi)
                    mlo = mhi = mhi.multiply(BigInteger.valueOf(10));
                else {
                    mlo = mlo.multiply(BigInteger.valueOf(10));
                    mhi = mhi.multiply(BigInteger.valueOf(10));
                }
            }
        }
        else
            for(i = 1;; i++) {
//                (char)(dig = quorem(b,S) + '0');
                BigInteger[] divResult = b.divideAndRemainder(S);
                b = divResult[1];
                dig = (char)(divResult[0].intValue() + '0');
                buf.append(dig);
                if (i >= ilim)
                    break;
                b = b.multiply(BigInteger.valueOf(10));
            }

        /* Round off last digit */

        b = b.shiftLeft(1);
        j = b.compareTo(S);
        if ((j > 0) || (j == 0 && (((dig & 1) == 1) || biasUp))) {
//        roundoff:
//            while(*--s == '9')
//                if (s == buf) {
//                    k++;
//                    *s++ = '1';
//                    goto ret;
//                }
//            ++*s++;
            if (roundOff(buf)) {
                k++;
                buf.append('1');
                return k + 1;
            }
        }
        else {
            stripTrailingZeroes(buf);
//            while(*--s == '0') ;
//            s++;
        }
//      ret:
//        Bfree(S);
//        if (mhi) {
//            if (mlo && mlo != mhi)
//                Bfree(mlo);
//            Bfree(mhi);
//        }
//      ret1:
//        Bfree(b);
//        JS_ASSERT(s < buf + bufsize);
        return k + 1;
    }

    private static void 
    stripTrailingZeroes(StringBuffer buf)
    {
//      while(*--s == '0') ;
//      s++;
        int bl = buf.length();
        while(bl-->0 && buf.charAt(bl) == '0');
        buf.setLength(bl + 1);
    }

    /* Mapping of JSDToStrMode -> JS_dtoa mode */
    private static final int dtoaModes[] = {
        0,   /* DTOSTR_STANDARD */
        0,   /* DTOSTR_STANDARD_EXPONENTIAL, */
        3,   /* DTOSTR_FIXED, */
        2,   /* DTOSTR_EXPONENTIAL, */
        2};  /* DTOSTR_PRECISION */

    static void
    JS_dtostr(StringBuffer buffer, int mode, int precision, double d)
    {
        int decPt;                                    /* Position of decimal point relative to first digit returned by JS_dtoa */
        boolean[] sign = new boolean[1];            /* true if the sign bit was set in d */
        int nDigits;                                /* Number of significand digits returned by JS_dtoa */

//        JS_ASSERT(bufferSize >= (size_t)(mode <= DTOSTR_STANDARD_EXPONENTIAL ? DTOSTR_STANDARD_BUFFER_SIZE :
//                DTOSTR_VARIABLE_BUFFER_SIZE(precision)));

        if (mode == DTOSTR_FIXED && (d >= 1e21 || d <= -1e21))
            mode = DTOSTR_STANDARD; /* Change mode here rather than below because the buffer may not be large enough to hold a large integer. */

        decPt = JS_dtoa(d, dtoaModes[mode], mode >= DTOSTR_FIXED, precision, sign, buffer);
        nDigits = buffer.length();

        /* If Infinity, -Infinity, or NaN, return the string regardless of the mode. */
        if (decPt != 9999) {
            boolean exponentialNotation = false;
            int minNDigits = 0;         /* Minimum number of significand digits required by mode and precision */
            int p;
            int q;

            switch (mode) {
                case DTOSTR_STANDARD:
                    if (decPt < -5 || decPt > 21)
                        exponentialNotation = true;
                    else
                        minNDigits = decPt;
                    break;

                case DTOSTR_FIXED:
                    if (precision >= 0)
                        minNDigits = decPt + precision;
                    else
                        minNDigits = decPt;
                    break;

                case DTOSTR_EXPONENTIAL:
//                    JS_ASSERT(precision > 0);
                    minNDigits = precision;
                    /* Fall through */
                case DTOSTR_STANDARD_EXPONENTIAL:
                    exponentialNotation = true;
                    break;

                case DTOSTR_PRECISION:
//                    JS_ASSERT(precision > 0);
                    minNDigits = precision;
                    if (decPt < -5 || decPt > precision)
                        exponentialNotation = true;
                    break;
            }

            /* If the number has fewer than minNDigits, pad it with zeros at the end */
            if (nDigits < minNDigits) {
                p = minNDigits;
                nDigits = minNDigits;
                do {
                    buffer.append('0');
                } while (buffer.length() != p);
            }

            if (exponentialNotation) {
                /* Insert a decimal point if more than one significand digit */
                if (nDigits != 1) {
                    buffer.insert(1, '.');
                }
                buffer.append('e');
                if ((decPt - 1) >= 0)
                    buffer.append('+');
                buffer.append(decPt - 1);
//                JS_snprintf(numEnd, bufferSize - (numEnd - buffer), "e%+d", decPt-1);
            } else if (decPt != nDigits) {
                /* Some kind of a fraction in fixed notation */
//                JS_ASSERT(decPt <= nDigits);
                if (decPt > 0) {
                    /* dd...dd . dd...dd */
                    buffer.insert(decPt, '.');
                } else {
                    /* 0 . 00...00dd...dd */
                    for (int i = 0; i < 1 - decPt; i++)
                        buffer.insert(0, '0');
                    buffer.insert(1, '.');
                }
            }
        }

        /* If negative and neither -0.0 nor NaN, output a leading '-'. */
        if (sign[0] &&
                !(word0(d) == Sign_bit && word1(d) == 0) &&
                !((word0(d) & Exp_mask) == Exp_mask &&
                  ((word1(d) != 0) || ((word0(d) & Frac_mask) != 0)))) {
            buffer.insert(0, '-');
        }
    }

}