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...