Tree Data Interface Descriptors
TDISHR Descriptors

A descriptor has information about a block of memory. All forms used in TDISHR have: 
        dsc$w_length    element length in bytes
        dsc$b_dtype     element data type
        dsc$b_class     descriptor type
        dsc$a_pointer   the address of the first element
DSC$K_CLASS_A descriptors add 
        dsc$b_scale     a binary or decimal scaling (not used in TDISHR)
        dsc$b_digits    decimal digits (not used in TDISHR)
        dsc$b_aflags    flag bits
        dsc$b_dimct     the number of dimensions
        dsc$l_arsize    number of bytes (digits or bits)
if dsc$b_aflags.dsc$v_fl_coeff also add 
        dsc$a_a0        address of index 0
        dsc$a_m[dsc$b_dimct] multipliers
followed by dsc$b_dimct pairs dsc$bounds.dsc$l_l and dsc$bounds.dsc$l_u, if dsc$b_aflags.dsc$v_fl_bounds is set. DSC$K_CLASS_R descriptors add dsc$b_ndesc in a longword as a count of the number of descriptor pointers that follow, maximum 255. DSC$K_CLASS_XD and DSC$K_CLASS_XS descriptors have a longword count of the number of bytes used, dsc$l_length. Class A data class is the form of the data, it is not the length or type. Some data types, however, appear in only certain classes. The classes used by TDISHR are: DSC$K_CLASS_S static, scalars of fixed length. DSC$K_CLASS_D dynamic, (text) scalar of varing length, dynamically allocated, limited to 65535 bytes. DSC$K_CLASS_A array, arrays of fixed element length. DSC$K_CLASS_XD extended dynamic, contiguous data block. DSC$K_CLASS_XS extended static, contiguous data block. DSC$K_CLASS_R record, a list of descriptor pointers and a single pointer to an operation code. DSC$K_CLASS_CA array descriptor with a pointer to further evaluate data, which is usually compress data. DATA(CLASS_CA) is a CLASS_A. DSC$K_CLASS_APD array of pointers to descriptors. EVALUATE(APD) is an array of the pointed-to objects. Class-R descriptors always have MDS types, excluding NIDs, PATHs, and EVENTs. The other MDS types appear in class-R descriptors and could be in CLASS_APD lists (not today). Class-XD descriptors are used to return any data form described by the pointed-to descriptors and thus will have DSC$K_DTYPE_DSC dtype. Dtype/Kind The kind (Fortran-90) or data type (VMS) of some information tells its characteristics. Logicals are stored in DTYPE_BU as 0 for false and 1 for true. Any integer type may be tested as a logical using the low bit. The unsigned integer dtypes are: DSC$K_DTYPE_BU byte unsigned (1 byte) DSC$K_DTYPE_WU word unsigned (2 bytes) DSC$K_DTYPE_LU longword unsigned (4 bytes) DSC$K_DTYPE_QU quadword unsigned (8 bytes) DSC$K_DTYPE_OU octaword unsigned (16 bytes) The two's-complement signed integer dtypes are: DSC$K_DTYPE_B byte signed (1 byte) DSC$K_DTYPE_W word signed (2 bytes) DSC$K_DTYPE_L longword signed (4 bytes) DSC$K_DTYPE_Q quadword signed (8 bytes) DSC$K_DTYPE_O octaword signed (16 bytes) The floating point real number types are: DSC$K_DTYPE_F float (24 bit fraction, 10^38 exponent range) DSC$K_DTYPE_D double (56 bit fraction, 10^38 exponent range) DSC$K_DTYPE_G double (52 bit fraction, 10^307 exponent range) DSC$K_DTYPE_H quad (113 bit fraction, 10^4931 exponent range) Two floating point reals are used to form complex number types: The real part is first and the imaginary part is second. DSC$K_DTYPE_FC float complex (8 bytes) DSC$K_DTYPE_DC double complex (16 bytes) DSC$K_DTYPE_GC double complex (16 bytes) DSC$K_DTYPE_HC quad complex (32 bytes) Text is: DSC$K_DTYPE_T ASCII text MDSplus "data" dtypes are: DSC$K_DTYPE_MISSING internal missing argument, 0 or blanks DSC$K_DTYPE_IDENT internal text-like form or variable name DSC$K_DTYPE_NID 4-byte node identifier. DSC$K_DTYPE_PATH text-like form of node identifier DSC$K_DTYPE_EVENT text-like form of event identifier MDSplus record (class-R) dtypes are: DSC$K_DTYPE_PARAM value, help, validation DSC$K_DTYPE_SIGNAL data, raw, dimensions DSC$K_DTYPE_DIMENSION window, axis DSC$K_DTYPE_WINDOW startidx, endidx, value_at_idx0 DSC$K_DTYPE_SLOPE axis with slope, [begin], [end],... DSC$K_DTYPE_FUNCTION arguments (uses word opcode) DSC$K_DTYPE_CONGLOM image, model, name, qualifiers DSC$K_DTYPE_RANGE begin, end, [delta] DSC$K_DTYPE_ACTION dispatch, task DSC$K_DTYPE_DISPATCH ident, phase, when, completion DSC$K_DTYPE_PROGRAM time_out, program DSC$K_DTYPE_ROUTINE time_out, image, routine, arguments DSC$K_DTYPE_PROCEDURE time_out, language, procedure, arguments DSC$K_DTYPE_METHOD time_out, method, object, arguments DSC$K_DTYPE_DEPENDENCY arguments (uses byte opcode) DSC$K_DTYPE_CONDITION condition (uses byte opcode) DSC$K_DTYPE_WITH_UNITS data, units DSC$K_DTYPE_CALL image, routine, arg...