Package nom.tam.util

Class ByteFormatter

  • public final class ByteFormatter
extends java.lang.Object
    This class provides mechanisms for efficiently formatting numbers and Strings. Data is appended to existing byte arrays. Note that the formatting of real or double values may differ slightly (in the last bit) from the standard Java packages since this routines are optimized for speed rather than accuracy.

    The methods in this class create no objects.

    If a number cannot fit into the requested space the truncateOnOverlow flag controls whether the formatter will attempt to append it using the available length in the output (a la C or Perl style formats). If this flag is set, or if the number cannot fit into space left in the buffer it is 'truncated' and the requested space is filled with a truncation fill character. A TruncationException may be thrown if the truncationThrow flag is set.

    This class does not explicitly support separate methods for formatting reals in exponential notation. Real numbers near one are by default formatted in decimal notation while numbers with large (or very negative) exponents are formatted in exponential notation. By setting the limits at which these transitions take place the user can force either exponential or decimal notation.

    • Constructor Summary

      Constructors 
      Constructor Description
      ByteFormatter()  

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      private int combineReal​(double val, byte[] buf, int off, int len, byte[] mant, int lmant, int shift)
      This method formats a double given a decimal mantissa and exponent information.
      int format​(boolean val, byte[] array)
      Format a boolean into an existing array.
      int format​(boolean val, byte[] array, int off, int len)
      Format a boolean into an existing array
      int format​(double val, byte[] array)
      Format a double into an array.
      int format​(double val, byte[] buf, int off, int len)
      Format a double into an existing character array.
      int format​(float val, byte[] array)
      Format a float into an array.
      int format​(float val, byte[] buf, int off, int len)
      Format a float into an existing byteacter array.
      int format​(int val, byte[] array)
      Format an int into an array.
      int format​(int val, byte[] buf, int off, int len)
      Format an int into an existing array.
      int format​(long val, byte[] array)
      Format a long into an array.
      int format​(long val, byte[] buf, int off, int len)
      Format a long into an existing array.
      int format​(java.lang.String val, byte[] array)
      Insert a string at the beginning of an array.
      int format​(java.lang.String val, byte[] array, int off, int len)
      Insert a String into an existing character array.
      private int mantissa​(byte[] mant, int lmant, int exp, boolean simple, byte[] buf, int off, int len)
      Write the mantissa of the number.
      private void truncationFiller​(byte[] buffer, int offset, int length)
      Fill the buffer with truncation characters.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • NEGATIVE_INFINITY

        public static final java.lang.String NEGATIVE_INFINITY
        See Also:
        Constant Field Values

      • DEFAULT_SIMPLE_MAX

        private static final double DEFAULT_SIMPLE_MAX
        Maximum magnitude to print in non-scientific notation.
        See Also:
        Constant Field Values

      • DEFAULT_SIMPLE_MIN

        private static final double DEFAULT_SIMPLE_MIN
        Minimum magnitude to print in non-scientific notation.
        See Also:
        Constant Field Values

      • DIGITS

        private static final byte[] DIGITS
        Digits. We could handle other bases by extending or truncating this list and changing the division by 10 (and it's factors) at various locations.

      • DOUBLE_EXPONENT_BIT_MASK

        private static final long DOUBLE_EXPONENT_BIT_MASK
        See Also:
        Constant Field Values

      • DOUBLE_EXPONENT_EXCESS

        private static final int DOUBLE_EXPONENT_EXCESS
        See Also:
        Constant Field Values

      • DOUBLE_EXPONENT_NORMALIZE_BIT

        private static final long DOUBLE_EXPONENT_NORMALIZE_BIT
        The hidden bit in normalized double numbers.
        See Also:
        Constant Field Values

      • DOUBLE_MIN_EXPONENT

        private static final int DOUBLE_MIN_EXPONENT
        Used to check if double is normalized
        See Also:
        Constant Field Values

      • FLOAT_EXPONENT_BIT_MASK

        private static final int FLOAT_EXPONENT_BIT_MASK
        See Also:
        Constant Field Values

      • FLOAT_EXPONENT_NORMALIZE_BIT

        private static final int FLOAT_EXPONENT_NORMALIZE_BIT
        The hidden bit in normalized floating point numbers.
        See Also:
        Constant Field Values

      • FLOAT_MIN_EXPONENT

        private static final int FLOAT_MIN_EXPONENT
        Used to check if float is normalized
        See Also:
        Constant Field Values

      • I_LOG_10

        private static final double I_LOG_10

      • MAXIMUM_SINGLE_DIGIT_INTEGER

        private static final int MAXIMUM_SINGLE_DIGIT_INTEGER
        The maximum single digit integer. Special case handling when rounding up and when incrementing the exponent.
        See Also:
        Constant Field Values

      • MAXIMUM_TWO_DIGIT_INTEGER

        private static final int MAXIMUM_TWO_DIGIT_INTEGER
        The maximum two digit integer. When we increment an exponent of this value, the exponent gets longer. Don't need to worry about 999 since exponents can't be that big.
        See Also:
        Constant Field Values

      • NUMBER_BASE

        private static final int NUMBER_BASE
        The underlying number base used in this class.
        See Also:
        Constant Field Values

      • NUMBER_BASE_POWERS

        private static final double[] NUMBER_BASE_POWERS
        Powers of 10. We over extend on both sides. These should perhaps be tabulated rather than computed though it may be faster to calculate them than to read in the extra bytes in the class file.

      • TRUNCATION_FILL

        private static final byte TRUNCATION_FILL
        What do we use to fill when we cannot print the number?Default is often used in Fortran.
        See Also:
        Constant Field Values

      • ZERO_POW

        private static final int ZERO_POW
        What index of tenpow is 10^0

      • tbuf1

        private final byte[] tbuf1
        Internal buffers used in formatting fields

      • tbuf2

        private final byte[] tbuf2

    • Constructor Detail

      • ByteFormatter

        public ByteFormatter()

    • Method Detail

      • combineReal

        private int combineReal​(double val,
                        byte[] buf,
                        int off,
                        int len,
                        byte[] mant,
                        int lmant,
                        int shift)
        This method formats a double given a decimal mantissa and exponent information.
        Parameters:
        val - The original number
        buf - Output buffer
        off - Offset into buffer
        len - Maximum number of characters to use in buffer.
        mant - A decimal mantissa for the number.
        lmant - The number of characters in the mantissa
        shift - The exponent of the power of 10 that we shifted val to get the given mantissa.
        Returns:
        Offset of next available character in buffer. @ * if the value was truncated

      • format

        public int format​(boolean val,
                  byte[] array)
        Format a boolean into an existing array.
        Parameters:
        val - value to write
        array - the array to fill
        Returns:
        Offset of next available character in buffer.

      • format

        public int format​(boolean val,
                  byte[] array,
                  int off,
                  int len)
        Format a boolean into an existing array
        Parameters:
        val - The boolean to be formatted
        array - The buffer in which to format the data.
        off - The starting offset within the buffer.
        len - The maximum number of characters to use use in formatting the number.
        Returns:
        Offset of next available character in buffer.

      • format

        public int format​(double val,
                  byte[] array)
        Format a double into an array.
        Parameters:
        val - The double to be formatted.
        array - The array in which to place the result.
        Returns:
        The number of characters used. @ * if the value was truncated

      • format

        public int format​(double val,
                  byte[] buf,
                  int off,
                  int len)
        Format a double into an existing character array.

        This is hard to do exactly right... The JDK code does stuff with rational arithmetic and so forth. We use a much simpler algorithm which may give an answer off in the lowest order bit. Since this is pure Java, it should still be consistent from machine to machine.

        Recall that the binary representation of the double is of the form d = 0.bbbbbbbb x 2n where there are up to 53 binary digits in the binary fraction (including the assumed leading 1 bit for normalized numbers). We find a value m such that 10m d is between 253 and 263. This product will be exactly convertible to a long with no loss of precision. Getting the decimal representation for that is trivial (see formatLong). This is a decimal mantissa and we have an exponent (-m). All we have to do is manipulate the decimal point to where we want to see it. Errors can arise due to roundoff in the scaling multiplication, but should be no more than a single bit.

        Parameters:
        val - Double to be formatted
        buf - Buffer in which result is to be stored
        off - Offset within buffer
        len - Maximum length of integer
        Returns:
        offset of next unused character in input buffer. @ * if the value was truncated

      • format

        public int format​(float val,
                  byte[] array)
        Format a float into an array.
        Parameters:
        val - The float to be formatted.
        array - The array in which to place the result.
        Returns:
        The number of characters used. @ * if the value was truncated

      • format

        public int format​(float val,
                  byte[] buf,
                  int off,
                  int len)
        Format a float into an existing byteacter array.

        This is hard to do exactly right... The JDK code does stuff with rational arithmetic and so forth. We use a much simpler algorithm which may give an answer off in the lowest order bit. Since this is pure Java, it should still be consistent from machine to machine.

        Recall that the binary representation of the float is of the form d = 0.bbbbbbbb x 2n where there are up to 24 binary digits in the binary fraction (including the assumed leading 1 bit for normalized numbers). We find a value m such that 10m d is between 224 and 232. This product will be exactly convertible to an int with no loss of precision. Getting the decimal representation for that is trivial (see formatInteger). This is a decimal mantissa and we have an exponent ( -m). All we have to do is manipulate the decimal point to where we want to see it. Errors can arise due to roundoff in the scaling multiplication, but should be very small.

        Parameters:
        val - Float to be formatted
        buf - Buffer in which result is to be stored
        off - Offset within buffer
        len - Maximum length of field
        Returns:
        Offset of next character in buffer. @ * if the value was truncated

      • format

        public int format​(int val,
                  byte[] array)
        Format an int into an array.
        Parameters:
        val - The int to be formatted.
        array - The array in which to place the result.
        Returns:
        The number of characters used. @ * if the value was truncated

      • format

        public int format​(int val,
                  byte[] buf,
                  int off,
                  int len)
        Format an int into an existing array.
        Parameters:
        val - Integer to be formatted
        buf - Buffer in which result is to be stored
        off - Offset within buffer
        len - Maximum length of integer
        Returns:
        offset of next unused character in input buffer.

      • format

        public int format​(long val,
                  byte[] array)
        Format a long into an array.
        Parameters:
        val - The long to be formatted.
        array - The array in which to place the result.
        Returns:
        The number of characters used. @ * if the value was truncated

      • format

        public int format​(long val,
                  byte[] buf,
                  int off,
                  int len)
        Format a long into an existing array.
        Parameters:
        val - Long to be formatted
        buf - Buffer in which result is to be stored
        off - Offset within buffer
        len - Maximum length of integer
        Returns:
        offset of next unused character in input buffer. @ * if the value was truncated

      • format

        public int format​(java.lang.String val,
                  byte[] array)
        Insert a string at the beginning of an array. * @return Offset of next available character in buffer.
        Parameters:
        val - The string to be inserted. A null string will insert len spaces.
        array - The buffer in which to insert the string.
        Returns:
        Offset of next available character in buffer.

      • format

        public int format​(java.lang.String val,
                  byte[] array,
                  int off,
                  int len)
        Insert a String into an existing character array. If the String is longer than len, then only the the initial len characters will be inserted.
        Parameters:
        val - The string to be inserted. A null string will insert len spaces.
        array - The buffer in which to insert the string.
        off - The starting offset to insert the string.
        len - The maximum number of characters to insert.
        Returns:
        Offset of next available character in buffer.

      • mantissa

        private int mantissa​(byte[] mant,
                     int lmant,
                     int exp,
                     boolean simple,
                     byte[] buf,
                     int off,
                     int len)
        Write the mantissa of the number. This method addresses the subtleties involved in rounding numbers.

      • truncationFiller

        private void truncationFiller​(byte[] buffer,
                              int offset,
                              int length)
        Fill the buffer with truncation characters. After filling the buffer, a TruncationException will be thrown if the appropriate flag is set.