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Member "mapm_4.9.5a/DOCS/struct.ref" (21 Feb 2010, 3670 Bytes) of package /linux/misc/old/mapm-4.9.5a.tar.gz:

    1 
    2 ============================================================================
    3           This file describes the format of the internal representation
    4       of an MAPM number in the M_APM data structure
    5           M. Ring   Nov 10, 2002
    6 ============================================================================
    7     
    8 struct  M_APM_struct {
    9     UCHAR   *m_apm_data;
   10     long    m_apm_id;
   11     int m_apm_refcount;
   12     int m_apm_malloclength;
   13     int m_apm_datalength;
   14     int m_apm_exponent;
   15     int m_apm_sign;
   16 };
   17 
   18 
   19 The internal representation of the number is in base 100. Each byte in
   20 'm_apm_data' can store the values 0-99 (out of a possible 0-255). All
   21 numbers mentioned here will be in decimal unless otherwise noted. Base 100
   22 was used since that is the largest power of 10 that will fit in one byte.
   23 A base that is a power of 10 was chosen since it is real convienent when
   24 translating to/from the internal format.
   25 
   26 All math operations will result in a 'normalized' number. In this context,
   27 normalized means 2 things; the first nibble of the first byte of data will
   28 be non-zero, and all trailing zero's will be ignored. As an example, 25 * 4
   29 would normally yield 100, or the digits '1', '0', '0' an have a 'datalength'
   30 of 3. Since the trailing zeros carry no information, the datalength will
   31 simply be truncated to 1. Note that this assumes the exponent is adjusted
   32 accordingly, which we of course do.
   33 
   34 The decimal point of the number is implied to be before the first byte of
   35 data. See the examples below.
   36 
   37 'm_apm_data'          : An array to hold the digits. The byte at offset 0 will
   38             contain the the first 2 (base 10) digits of the number
   39             (or 1 base 100 digit), the next byte will contain the 
   40             3rd and 4th digits, etc. If the number has an odd 
   41             number of digits, the least significant nibble in the 
   42             last byte of data will be 0.
   43 
   44 'm_apm_id'            : Set during m_apm_init to M_APM_IDENT. Used to
   45             validate the structure before the call to 'free'.
   46 
   47 'm_apm_refcount'      : NOT used by the basic M_APM. It was added to support 
   48             the C++ MAPM wrapper class. (However, we do initialize
   49             this element to 1).
   50 
   51 'm_apm_malloclength'  : Keeps track of how many bytes were allocated in the
   52             malloc call to m_apm_data. If a given math operation
   53             will yield a result that won't fit into the existing
   54             m_apm_data array, we will realloc m_apm_data so it
   55             will be guaranteed to hold the result.
   56 
   57 'm_apm_datalength'    : The number of base 10 digits in the number. In other
   58             words, the number 5678 will have a datalength of 4
   59             (which will fit into 2 bytes). The number 1234567 will
   60             have a datalength of 7 (which requires 4 bytes to
   61             store).
   62 
   63 'm_apm_exponent'      : The exponent of the number, can be up to sizeof(int)
   64 
   65 'm_apm_sign'          : The sign of the number. sign = -1 is a negative
   66             number. sign = +1 is a positive number. sign = 0 is
   67             a number that is exactly 0. This feature is used
   68             extensively in the library for fast comparisons to 0.
   69 
   70 --------
   71 Examples
   72 --------
   73 
   74 number          sign  datalength  exponent  data: [byte 0,1,2, etc]
   75 -----------------------------------------------------------------------
   76 0                 0       1           0     00
   77 
   78 4.0              +1       1          +1     40       (data = 28h)
   79 
   80 -0.07            -1       1          -1     70       (data = 46h)
   81 
   82 31.6             +1       3          +2     31, 60   (data = 1Fh, 3Ch)
   83 
   84 -52338.226       -1       8          +5     52, 33, 82, 26
   85 
   86 0.0007621        +1       4          -3     76, 21
   87 
   88 3.75900064E+18   +1       9         +19     37, 59, 00, 06, 40
   89 
   90 -6.1289E-7       -1       5          -6     61, 28, 90
   91 
   92 0.872394         +1       6           0     87, 23, 94
   93