Document revision date: 19 July 1999

Guidelines for Using LIB$CVT_DX_DX

The data type and descriptor class of the source and destination arguments determine how LIB$CVT_DX_DX performs the conversion, according to the following rules:

• Scale is applied when indicated in the descriptor (descriptor CLASS_SD only), and scaling is defined for the data type.
• No language-specific semantics are applied, such as BASIC scale for DSC$K_DTYPE_D.
• Some conversions must use intermediate values to arrive at the destination requested. Although some loss of speed is inevitable, intermediate values will not cause a loss of precision.
• Results are always rounded instead of truncated, except for the case described below. Note that loss of precision or range may be inherent in the destination data type or in the NBDS destination size. No errors are reported if there is a loss of precision or range as a result of destination data type.
• When the destination is an NBDS and has fixed-string semantics, then if the source does not fill the destination, the destination is padded with blanks.
• When the source and destination are both NBDS and no scaling is requested, then a straight copy is done without translation or conversion, and truncation is possible. If scaling is requested, then a conversion takes place as defined in Table lib-2.
• When the source is an NBDS and the destination is non-NBDS, if there is an invalid character in the source or the value is outside the range that can be represented by the destination, then LIB$_INVNBDS is returned.
• Attempts to convert a negative value to an unsigned data type cause the LIB$_INVCVT error to be returned.
• If the destination is an NBDS of descriptor CLASS_D, then a new string of appropriate size is allocated for it, if necessary.
• Invalid conversions resulting in an error produce an unpredictable result.

Use of Numeric Byte Data Strings (NBDS)

For simplicity, and to define a generic numeric string that LIB$CVT_DX_DX understands to be a numeric string, the set Numeric Byte Data String (NBDS) is defined to be the set of NBDS descriptors shown in Table lib-1.

The combination of data type and descriptor class determines whether an argument is an NBDS. For example, LIB$CVT_DX_DX treats the combination DSC$K_DTYPE_B/DSC$K_CLASS_S (unsigned byte scalar) as an atomic data type. However, the routine considers DSC$K_DTYPE_BU/DSC$K_CLASS_NCA (noncontiguous array of unsigned bytes) to be an NBDS.

A destination NBDS is always left-justified.

If a destination NBDS requires more than 50 digits for its format (including the sign, if any), then it is expressed in exponential format.

For a conversion of NBDS to NBDS, this format is used if scaling is requested. Otherwise, a straight copy is done. The format of a source NBDS is the same as the format defined for the input argument inp in OTS$_CVT_T_z, with bits 0, 2, and 4 set in the flags argument. That is, blanks are ignored, underflow causes an error, and tabs are ignored.

Table lib-2 defines the format of a destination NBDS.

Table lib-2 LIB$CVT_DX_DX Destination NBDS Formats

Source Data Type	Destination NBDS Format
Byte integer (signed)	sdigits
Byte (unsigned)	digits
Word integer (signed)	sdigits
Word (unsigned)	digits
Longword integer (signed)	sdigits
Longword (unsigned)	digits
Quadword integer (signed)	sdigits
D_floating	s0.min(16,w-7)E+ or - nn
F_floating	s0.min( 7,w-7)E+ or - nn
G_floating	s0.min(15,w-8)E+ or - nnn
H_floating	s0.min(33,w-9)E+ or - nnnn
FS_floating (IEEE)	s0.min(7,w-7)E+ or - nn
FT_floating (IEEE)	s0.min(15,w-8)E+ or - nnn
NBDS	s0.min(33,w-9)E+ or - nnnn
Decimal string	sdigits (as defined by VAX architecture)

• digits: Digits 0 through 9, and a decimal point only if source descriptor specifies the value of the SCALE field as less than 0.
• w: Width of destination in bytes.
• s: Sign. For positive numbers, the sign is implied.
• min: Minimum of two values.

The A and NCA array descriptor classes are supported with the following restrictions:

An array is written with the semantics of a fixed string.
DIMCT = 1	Only one-dimensional arrays are recognized.
LENGTH = 1	The length of each array element must be a byte.
ARSIZE <= 65,535	The total size of the array must be less than 65,535 bytes. If ARSIZE = 0, the array has a length of zero.
S1 = 1	The stride of an array passed by a noncontiguous array descriptor must be 1. That is, even if the class of the array's descriptor is noncontiguous array (NCA), the array itself must be contiguous.

For more information about the semantics of writing output strings, see the OpenVMS RTL String Manipulation (STR$) Manual.

If the calling program passes a descriptor to LIB$CVT_DX_DX that does not comply with Table lib-1, one of the following error messages is returned:

• LIB$_INVDTYDSC
• LIB$_INVCLADSC
• LIB$_INVCLADTY
• LIB$_INVNBDS

Condition Values Returned

SS$_NORMAL	Routine successfully completed.
LIB$_DECOVF	Packed decimal overflow error. Severe error.
LIB$_FLTOVF	Floating overflow error. Severe error.
LIB$_FLTUND	Floating underflow error. Severe error.
LIB$_INTOVF	Integer overflow error. Severe error.
LIB$_INVCLADSC	Invalid class in descriptor. This class of descriptor is not supported. Severe error.
LIB$_INVCLADTY	Invalid class and data type in descriptor. This class and data type combination is not supported. Severe error.
LIB$_INVCVT	If the source value is negative and the destination data type is unsigned, this error is returned.
LIB$_INVDTYDSC	Invalid data type in descriptor. This data type is not supported. Severe error.
LIB$_INVNBDS	Invalid NBDS. There is an invalid character in the input, or the value is outside the range that can be represented by the destination, or the NMDS descriptor is invalid. This error is also signaled when the array size of an NBDS is larger than 65,535 bytes or the array is multi-dimensional.
LIB$_OUTSTRTRU	Output string truncated. This is returned only when NBDS is both source and destination and no scaling is requested. The result is truncated.
LIB$_ROPRAND	Reserved operand error. Severe error.

The Convert Internal Time to External Time routine converts an internal OpenVMS system time (either absolute or delta) into an external time.

Format

LIB$CVT_FROM_INTERNAL_TIME operation ,resultant-time [,input-time]

RETURNS

OpenVMS usage:	cond_value
type:	longword (unsigned)
access:	write only
mechanism:	by value

Arguments

operation

OpenVMS usage:	function_code
type:	longword (unsigned)
access:	read only
mechanism:	by reference

The conversion to be performed. The operation argument is the address of an unsigned longword containing the operation. The following table shows valid values for operation:

Operation	Type	Return Range
LIB$K_MONTH_OF_YEAR	Absolute	1 to 12
LIB$K_DAY_OF_YEAR	Absolute	1 to 366
LIB$K_HOUR_OF_YEAR	Absolute	1 to 8784
LIB$K_MINUTE_OF_YEAR	Absolute	1 to 527,040
LIB$K_SECOND_OF_YEAR	Absolute	1 to 31,622,400
LIB$K_DAY_OF_MONTH	Absolute	1 to 31
LIB$K_HOUR_OF_MONTH	Absolute	1 to 744
LIB$K_MINUTE_OF_MONTH	Absolute	1 to 44,640
LIB$K_SECOND_OF_MONTH	Absolute	1 to 2,678,400
LIB$K_DAY_OF_WEEK	Absolute 1	1 to 7
LIB$K_HOUR_OF_WEEK	Absolute 2	1 to 168
LIB$K_MINUTE_OF_WEEK	Absolute 3	1 to 10,080
LIB$K_SECOND_OF_WEEK	Absolute 4	1 to 604,800
LIB$K_HOUR_OF_DAY	Absolute	0 to 23
LIB$K_MINUTE_OF_DAY	Absolute	0 to 1439
LIB$K_SECOND_OF_DAY	Absolute	0 to 86,399
LIB$K_MINUTE_OF_HOUR	Absolute	0 to 59
LIB$K_SECOND_OF_HOUR	Absolute	0 to 3599
LIB$K_SECOND_OF_MINUTE	Absolute	0 to 59
LIB$K_JULIAN_DATE	Absolute 5	Julian date
LIB$K_DELTA_WEEKS	Delta 6
LIB$K_DELTA_DAYS	Delta 7
LIB$K_DELTA_HOURS	Delta 8
LIB$K_DELTA_MINUTES	Delta 9
LIB$K_DELTA_SECONDS	Delta 10

resultant-time

input-time

Description

LIB$CVT_FROM_INTERNAL_TIME converts an internal OpenVMS system time (either absolute or delta) into an external time. The operation argument specifies the conversion. LIB$CVT_FROM_INTERNAL_TIME converts the value of input-time (or the current system time if input-time is not supplied) into one of the external formats listed in the operation argument description. LIB$CVT_FROM_INTERNAL_TIME then places the result into resultant-time.

See the OpenVMS Programming Concepts Manual for a description of system date and time operations as well as a detailed description of the format mnemonics used in these routines.

Condition Values Returned

LIB$_NORMAL	Routine successfully completed.
LIB$_ABSTIMREQ	Absolute time required but delta time supplied.
LIB$_DELTIMREQ	Delta time required but absolute time supplied.
LIB$_INVOPER	Invalid operation.
LIB$_IVTIME	Invalid time.
LIB$_WRONUMARG	Incorrect number of arguments.

The Convert External Time to Internal Time routine converts an external time interval into an OpenVMS internal format delta time.

Format

LIB$CVT_TO_INTERNAL_TIME operation ,input-time ,resultant-time

RETURNS

OpenVMS usage:	cond_value
type:	longword (unsigned)
access:	write only
mechanism:	by value

Arguments

operation

OpenVMS usage:	function_code
type:	longword (unsigned)
access:	read only
mechanism:	by reference

The conversion to be performed. The operation argument is the address of an unsigned longword specifying the operation. Valid values for operation are the following:

Operation	Interpretation
LIB$K_DELTA_WEEKS	Whole weeks in delta time
LIB$K_DELTA_DAYS	Whole days in delta time
LIB$K_DELTA_HOURS	Whole hours in delta time
LIB$K_DELTA_MINUTES	Whole minutes in delta time
LIB$K_DELTA_SECONDS	Whole seconds in delta time

input-time

OpenVMS usage:	varying_arg
type:	longword (signed)
access:	read only
mechanism:	by reference

Delta time to be converted. The input-time argument is the address of this input time. The value you supply for input-time must be greater than 0.

resultant-time

OpenVMS usage:	date_time
type:	quadword (unsigned)
access:	write only
mechanism:	by reference

The OpenVMS internal format delta time that results from the conversion. The resultant-time argument is the address of an unsigned quadword containing the result.

Description

LIB$CVT_TO_INTERNAL_TIME converts an external time interval, such as three weeks, into an OpenVMS internal format delta time. The operation argument specifies the conversion. LIB$_CVT_TO_INTERNAL_TIME converts the value of input-time into one of the internal format delta times listed in the operation argument description. LIB$_CVT_TO_INTERNAL_TIME then places the result into resultant-time.

See the OpenVMS Programming Concepts Manual for a description of system date and time operations as well as a detailed description of the format mnemonics used in these routines.

Condition Values Returned

LIB$_NORMAL	Routine successfully completed.
LIB$_INVOPER	Invalid operation.
LIB$_IVTIME	Invalid time.
LIB$_WRONUMARG	Incorrect number of arguments.

The Convert 7-Word Vector to Internal Time routine converts a 7-word vector into an OpenVMS internal format delta or absolute time.

Format

LIB$CVT_VECTIM input-time ,resultant-time

RETURNS

OpenVMS usage:	cond_value
type:	longword (unsigned)
access:	write only
mechanism:	by value

Arguments

input-time

OpenVMS usage:	vector_word_unsigned
type:	word (unsigned)
access:	read only
mechanism:	by reference, array reference

Time to be converted. The input-time argument is the address of a 7-word structure containing this time. This vector directly corresponds to a $NUMTIM timbuf structure. The following diagram depicts the fields in this structure:

The input-time argument can represent an absolute or a delta time. In order for input-time to represent a delta time, the year since 0 and month of year fields must equal zero. If those fields do not equal zero, an absolute time is returned.

resultant-time

Description

LIB$CVT_VECTIM converts a 7-word vector (in the format output by the $NUMTIM system service) into an OpenVMS internal format delta or absolute time. LIB$CVT_VECTIM then places the result into resultant-time.

See the OpenVMS System Services Reference Manual for more information about $NUMTIM.

Condition Values Returned

LIB$_NORMAL	Routine successfully completed.
LIB$_IVTIME	Invalid time.
LIB$_WRONUMARG	Incorrect number of arguments.

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