src/main/java/com/fasterxml/jackson/core/io/NumberOutput.java

package com.fasterxml.jackson.core.io;

public final class NumberOutput
{
    private static int MILLION = 1000000;
    private static int BILLION = 1000000000;
    private static long BILLION_L = 1000000000L;

    private static long MIN_INT_AS_LONG = (long) Integer.MIN_VALUE;
    private static long MAX_INT_AS_LONG = (long) Integer.MAX_VALUE;

    final static String SMALLEST_INT = String.valueOf(Integer.MIN_VALUE);
    final static String SMALLEST_LONG = String.valueOf(Long.MIN_VALUE);

    /**
     * Encoded representations of 3-decimal-digit indexed values, where
     * 3 LSB are ascii characters
     *
     * @since 2.8.2
     */
    private final static int[] TRIPLET_TO_CHARS = new int[1000];

    static {
        /* Let's fill it with NULLs for ignorable leading digits,
         * and digit chars for others
         */
        int fullIx = 0;
        for (int i1 = 0; i1 < 10; ++i1) {
            for (int i2 = 0; i2 < 10; ++i2) {
                for (int i3 = 0; i3 < 10; ++i3) {
                    int enc = ((i1 + '0') << 16)
                            | ((i2 + '0') << 8)
                            | (i3 + '0');
                    TRIPLET_TO_CHARS[fullIx++] = enc;
                }
            }
        }
    }

    private final static String[] sSmallIntStrs = new String[] {
        "0","1","2","3","4","5","6","7","8","9","10"
    };
    private final static String[] sSmallIntStrs2 = new String[] {
        "-1","-2","-3","-4","-5","-6","-7","-8","-9","-10"
    };

    /*
    /**********************************************************
    /* Efficient serialization methods using raw buffers
    /**********************************************************
     */

    /**
     * @return Offset within buffer after outputting int
     */
    public static int outputInt(int v, char[] b, int off)
    {
        if (v < 0) {
            if (v == Integer.MIN_VALUE) {
                // Special case: no matching positive value within range;
                // let's then "upgrade" to long and output as such.
                return _outputSmallestI(b, off);
            }
            b[off++] = '-';
            v = -v;
        }

        if (v < MILLION) { // at most 2 triplets...
            if (v < 1000) {
                if (v < 10) {
                    b[off] = (char) ('0' + v);
                    return off+1;
                }
                return _leading3(v, b, off);
            }
            int thousands = v / 1000;
            v -= (thousands * 1000); // == value % 1000
            off = _leading3(thousands, b, off);
            off = _full3(v, b, off);
            return off;
        }

        // ok, all 3 triplets included
        /* Let's first hand possible billions separately before
         * handling 3 triplets. This is possible since we know we
         * can have at most '2' as billion count.
         */
        if (v >= BILLION) {
            v -= BILLION;
            if (v >= BILLION) {
                v -= BILLION;
                b[off++] = '2';
            } else {
                b[off++] = '1';
            }
            return _outputFullBillion(v, b, off);
        }
        int newValue = v / 1000;
        int ones = (v - (newValue * 1000)); // == value % 1000
        v = newValue;
        newValue /= 1000;
        int thousands = (v - (newValue * 1000));
        
        off = _leading3(newValue, b, off);
        off = _full3(thousands, b, off);
        return _full3(ones, b, off);
    }

    public static int outputInt(int v, byte[] b, int off)
    {
        if (v < 0) {
            if (v == Integer.MIN_VALUE) {
                return _outputSmallestI(b, off);
            }
            b[off++] = '-';
            v = -v;
        }

        if (v < MILLION) { // at most 2 triplets...
            if (v < 1000) {
                if (v < 10) {
                    b[off++] = (byte) ('0' + v);
                } else {
                    off = _leading3(v, b, off);
                }
            } else {
                int thousands = v / 1000;
                v -= (thousands * 1000); // == value % 1000
                off = _leading3(thousands, b, off);
                off = _full3(v, b, off);
            }
            return off;
        }
        if (v >= BILLION) {
            v -= BILLION;
            if (v >= BILLION) {
                v -= BILLION;
                b[off++] = '2';
            } else {
                b[off++] = '1';
            }
            return _outputFullBillion(v, b, off);
        }
        int newValue = v / 1000;
        int ones = (v - (newValue * 1000)); // == value % 1000
        v = newValue;
        newValue /= 1000;
        int thousands = (v - (newValue * 1000));
        off = _leading3(newValue, b, off);
        off = _full3(thousands, b, off);
        return _full3(ones, b, off);
    }

    /**
     * @return Offset within buffer after outputting int
     */
    public static int outputLong(long v, char[] b, int off)
    {
        // First: does it actually fit in an int?
        if (v < 0L) {
            if (v > MIN_INT_AS_LONG) {
                return outputInt((int) v, b, off);
            }
            if (v == Long.MIN_VALUE) {
                return _outputSmallestL(b, off);
            }
            b[off++] = '-';
            v = -v;
        } else {
            if (v <= MAX_INT_AS_LONG) {
                return outputInt((int) v, b, off);
            }
        }

        // Ok, let's separate last 9 digits (3 x full sets of 3)
        long upper = v / BILLION_L;
        v -= (upper * BILLION_L);

        // two integers?
        if (upper < BILLION_L) {
            off = _outputUptoBillion((int) upper, b, off);
        } else {
            // no, two ints and bits; hi may be about 16 or so
            long hi = upper / BILLION_L;
            upper -= (hi * BILLION_L);
            off = _leading3((int) hi, b, off);
            off = _outputFullBillion((int) upper, b, off);
        }
        return _outputFullBillion((int) v, b, off);
    }

    public static int outputLong(long v, byte[] b, int off)
    {
        if (v < 0L) {
            if (v > MIN_INT_AS_LONG) {
                return outputInt((int) v, b, off);
            }
            if (v == Long.MIN_VALUE) {
                return _outputSmallestL(b, off);
            }
            b[off++] = '-';
            v = -v;
        } else {
            if (v <= MAX_INT_AS_LONG) {
                return outputInt((int) v, b, off);
            }
        }

        // Ok, let's separate last 9 digits (3 x full sets of 3)
        long upper = v / BILLION_L;
        v -= (upper * BILLION_L);

        // two integers?
        if (upper < BILLION_L) {
            off = _outputUptoBillion((int) upper, b, off);
        } else {
            // no, two ints and bits; hi may be about 16 or so
            long hi = upper / BILLION_L;
            upper -= (hi * BILLION_L);
            off = _leading3((int) hi, b, off);
            off = _outputFullBillion((int) upper, b, off);
        }
        return _outputFullBillion((int) v, b, off);
    }

    /*
    /**********************************************************
    /* Convenience serialization methods
    /**********************************************************
     */

    /* !!! 05-Aug-2008, tatus: Any ways to further optimize
     *   these? (or need: only called by diagnostics methods?)
     */
    public static String toString(int v)
    {
        // Lookup table for small values
        if (v < sSmallIntStrs.length) {
            if (v >= 0) {
                return sSmallIntStrs[v];
            }
            int v2 = -v - 1;
            if (v2 < sSmallIntStrs2.length) {
                return sSmallIntStrs2[v2];
            }
        }
        return Integer.toString(v);
    }

    public static String toString(long v) {
        if (v <= Integer.MAX_VALUE && v >= Integer.MIN_VALUE) {
            return toString((int) v);
        }
        return Long.toString(v);
    }

    public static String toString(double v) {
        return Double.toString(v);
    }

    /**
     * @since 2.6.0
     */
    public static String toString(float v) {
        return Float.toString(v);
    }

    /*
    /**********************************************************
    /* Internal helper methods
    /**********************************************************
     */

    private static int _outputUptoBillion(int v, char[] b, int off)
    {
        if (v < MILLION) { // at most 2 triplets...
            if (v < 1000) {
                return _leading3(v, b, off);
            }
            int thousands = v / 1000;
            int ones = v - (thousands * 1000); // == value % 1000
            return _outputUptoMillion(b, off, thousands, ones);
        }
        int thousands = v / 1000;
        int ones = (v - (thousands * 1000)); // == value % 1000
        int millions = thousands / 1000;
        thousands -= (millions * 1000);

        off = _leading3(millions, b, off);

        int enc = TRIPLET_TO_CHARS[thousands];
        b[off++] = (char) (enc >> 16);
        b[off++] = (char) ((enc >> 8) & 0x7F);
        b[off++] = (char) (enc & 0x7F);

        enc = TRIPLET_TO_CHARS[ones];
        b[off++] = (char) (enc >> 16);
        b[off++] = (char) ((enc >> 8) & 0x7F);
        b[off++] = (char) (enc & 0x7F);

        return off;
    }
    
    private static int _outputFullBillion(int v, char[] b, int off)
    {
        int thousands = v / 1000;
        int ones = (v - (thousands * 1000)); // == value % 1000
        int millions = thousands / 1000;

        int enc = TRIPLET_TO_CHARS[millions];
        b[off++] = (char) (enc >> 16);
        b[off++] = (char) ((enc >> 8) & 0x7F);
        b[off++] = (char) (enc & 0x7F);

        thousands -= (millions * 1000);
        enc = TRIPLET_TO_CHARS[thousands];
        b[off++] = (char) (enc >> 16);
        b[off++] = (char) ((enc >> 8) & 0x7F);
        b[off++] = (char) (enc & 0x7F);

        enc = TRIPLET_TO_CHARS[ones];
        b[off++] = (char) (enc >> 16);
        b[off++] = (char) ((enc >> 8) & 0x7F);
        b[off++] = (char) (enc & 0x7F);

        return off;
    }
    
    private static int _outputUptoBillion(int v, byte[] b, int off)
    {
        if (v < MILLION) { // at most 2 triplets...
            if (v < 1000) {
                return _leading3(v, b, off);
            }
            int thousands = v / 1000;
            int ones = v - (thousands * 1000); // == value % 1000
            return _outputUptoMillion(b, off, thousands, ones);
        }
        int thousands = v / 1000;
        int ones = (v - (thousands * 1000)); // == value % 1000
        int millions = thousands / 1000;
        thousands -= (millions * 1000);

        off = _leading3(millions, b, off);

        int enc = TRIPLET_TO_CHARS[thousands];
        b[off++] = (byte) (enc >> 16);
        b[off++] = (byte) (enc >> 8);
        b[off++] = (byte) enc;

        enc = TRIPLET_TO_CHARS[ones];
        b[off++] = (byte) (enc >> 16);
        b[off++] = (byte) (enc >> 8);
        b[off++] = (byte) enc;

        return off;
    }

    private static int _outputFullBillion(int v, byte[] b, int off)
    {
        int thousands = v / 1000;
        int ones = (v - (thousands * 1000)); // == value % 1000
        int millions = thousands / 1000;
        thousands -= (millions * 1000);

        int enc = TRIPLET_TO_CHARS[millions];
        b[off++] = (byte) (enc >> 16);
        b[off++] = (byte) (enc >> 8);
        b[off++] = (byte) enc;

        enc = TRIPLET_TO_CHARS[thousands];
        b[off++] = (byte) (enc >> 16);
        b[off++] = (byte) (enc >> 8);
        b[off++] = (byte) enc;

        enc = TRIPLET_TO_CHARS[ones];
        b[off++] = (byte) (enc >> 16);
        b[off++] = (byte) (enc >> 8);
        b[off++] = (byte) enc;

        return off;
    }

    private static int _outputUptoMillion(char[] b, int off, int thousands, int ones)
    {
        int enc = TRIPLET_TO_CHARS[thousands];
        if (thousands > 9) {
            if (thousands > 99) {
                b[off++] = (char) (enc >> 16);
            }
            b[off++] = (char) ((enc >> 8) & 0x7F);
        }
        b[off++] = (char) (enc & 0x7F);
        // and then full
        enc = TRIPLET_TO_CHARS[ones];
        b[off++] = (char) (enc >> 16);
        b[off++] = (char) ((enc >> 8) & 0x7F);
        b[off++] = (char) (enc & 0x7F);
        return off;
    }

    private static int _outputUptoMillion(byte[] b, int off, int thousands, int ones)
    {
        int enc = TRIPLET_TO_CHARS[thousands];
        if (thousands > 9) {
            if (thousands > 99) {
                b[off++] = (byte) (enc >> 16);
            }
            b[off++] = (byte) (enc >> 8);
        }
        b[off++] = (byte) enc;
        // and then full
        enc = TRIPLET_TO_CHARS[ones];
        b[off++] = (byte) (enc >> 16);
        b[off++] = (byte) (enc >> 8);
        b[off++] = (byte) enc;
        return off;
    }
    
    private static int _leading3(int t, char[] b, int off)
    {
        int enc = TRIPLET_TO_CHARS[t];
        if (t > 9) {
            if (t > 99) {
                b[off++] = (char) (enc >> 16);
            }
            b[off++] = (char) ((enc >> 8) & 0x7F);
        }
        b[off++] = (char) (enc & 0x7F);
        return off;
    }

    private static int _leading3(int t, byte[] b, int off)
    {
        int enc = TRIPLET_TO_CHARS[t];
        if (t > 9) {
            if (t > 99) {
                b[off++] = (byte) (enc >> 16);
            }
            b[off++] = (byte) (enc >> 8);
        }
        b[off++] = (byte) enc;
        return off;
    }

    private static int _full3(int t, char[] b, int off)
    {
        int enc = TRIPLET_TO_CHARS[t];
        b[off++] = (char) (enc >> 16);
        b[off++] = (char) ((enc >> 8) & 0x7F);
        b[off++] = (char) (enc & 0x7F);
        return off;
    }

    private static int _full3(int t, byte[] b, int off)
    {
        int enc = TRIPLET_TO_CHARS[t];
        b[off++] = (byte) (enc >> 16);
        b[off++] = (byte) (enc >> 8);
        b[off++] = (byte) enc;
        return off;
    }

    // // // Special cases for where we can not flip the sign bit

    private static int _outputSmallestL(char[] b, int off)
    {
        int len = SMALLEST_LONG.length();
        SMALLEST_LONG.getChars(0, len, b, off);
        return (off + len);
    }

    private static int _outputSmallestL(byte[] b, int off)
    {
        int len = SMALLEST_LONG.length();
        for (int i = 0; i < len; ++i) {
            b[off++] = (byte) SMALLEST_LONG.charAt(i);
        }
        return off;
    }

    private static int _outputSmallestI(char[] b, int off)
    {
        int len = SMALLEST_INT.length();
        SMALLEST_INT.getChars(0, len, b, off);
        return (off + len);
    }

    private static int _outputSmallestI(byte[] b, int off)
    {
        int len = SMALLEST_INT.length();
        for (int i = 0; i < len; ++i) {
            b[off++] = (byte) SMALLEST_INT.charAt(i);
        }
        return off;
    }
}