The Convert Floating-Point Data Type routine converts floating-
point data types to other supported floating-point data types and
allows additional control over the converted results.
Format
status = CVT$FTOF input_value, input_type_code, output_value,
output_type_code, options
1 – Returns
OpenVMS usage:mask_longword
type: longword (unsigned)
access: write only
mechanism: by value
The status return value is an unsigned longword bit mask
containing the condition codes raised by the function. CVT$FTOF
returns CVT$K_NORMAL; otherwise, it sets one or more recoverable
and unrecoverable conditions.
Return status values are in the $CVTDEF module in the system
symbol libraries.
2 – Arguments
input_value
OpenVMS usage:varying_arg
type: unspecified
access: read only
mechanism: by reference
The address of a data area containing a floating-point number to
be converted. The number can be floating-point data in one of the
following formats:
F_Floating Big_Endian_IEEE_S_Floating
D_Floating Big_Endian_IEEE_T_Floating
G_Floating Big_Endian_IEEE_X_Floating
H_Floating IBM_Long_Floating
IEEE_S_Floating IBM_Short_Floating
IEEE_T_Floating CRAY_Floating_Single
IEEE_X_Floating
The value of the input_type_code argument determines the format
and size of the input_value argument.
input_type_code
OpenVMS usage:longword_unsigned
type: longword (unsigned)
access: read only
mechanism: by value
The value of a longword bit mask specifying the type of floating-
point data being passed in the input_value argument. Valid type
codes are:
Size in
Input_type_code Format Bytes
CVT$K_VAX_F F_Floating 4
CVT$K_VAX_D D_Floating 8
CVT$K_VAX_G G_Floating 8
CVT$K_VAX_H H_Floating 16
CVT$K_IEEE_S IEEE_S_Floating 4
CVT$K_IEEE_T IEEE_T_Floating 8
CVT$K_IEEE_X IEEE_X_Floating 16
CVT$K_BIG_ENDIAN_IEEE_S Big_Endian_IEEE_S_Floating 4
CVT$K_BIG_ENDIAN_IEEE_T Big_Endian_IEEE_T_Floating 8
CVT$K_BIG_ENDIAN_IEEE_X Big_Endian_IEEE_X_Floating 16
CVT$K_IBM_LONG IBM_Long_Floating 8
CVT$K_IBM_SHORT IBM_Short_Floating 4
CVT$K_CRAY_SINGLE CRAY_Floating 8
Declarations for the input_type_code argument are in the $CVTDEF
module found in the system symbol libraries.
output_value
OpenVMS usage:varying_arg
type: unspecified
access: write only
mechanism: by reference
The address of a data area that receives the converted floating-
point number. The number can be floating-point data in F_
Floating, D_Floating, G_Floating, H_Floating, IEEE_S_Floating,
IEEE_T_Floating, IEEE_X_Floating, Big_Endian_IEEE_S_Floating,
Big_Endian_IEEE_T_Floating, Big_Endian_IEEE_X_Floating, IBM_Long_
Floating, IBM_Short_Floating, or CRAY_Floating_Single format. The
value of the output_type_code argument determines the size and
format of the converted floating-point number.
output_type_code
OpenVMS usage:longword_unsigned
type: longword (unsigned)
access: read only
mechanism: by value
The value of a longword bit mask specifying the type of floating-
point data that the input_value argument will be converted into
and returned in the output_value argument. Valid type codes are:
Size in
Output_type_code Format Bytes
CVT$K_VAX_F F_Floating 4
CVT$K_VAX_D D_Floating 8
CVT$K_VAX_G G_Floating 8
CVT$K_VAX_H H_Floating 16
CVT$K_IEEE_S IEEE_S_Floating 4
CVT$K_IEEE_T IEEE_T_Floating 8
CVT$K_IEEE_X IEEE_X_Floating 16
CVT$K_BIG_ENDIAN_IEEE_S Big_Endian_IEEE_S_Floating 4
CVT$K_BIG_ENDIAN_IEEE_T Big_Endian_IEEE_T_Floating 8
CVT$K_BIG_ENDIAN_IEEE_X Big_Endian_IEEE_X_Floating 16
CVT$K_IBM_LONG IBM_Long_Floating 8
CVT$K_IBM_SHORT IBM_Short_Floating 4
CVT$K_CRAY_SINGLE CRAY_Floating 8
Declarations for the output_type_code argument are in the $CVTDEF
module found in the system symbol libraries.
options
OpenVMS usage:mask_longword
type: longword (unsigned)
access: read only
mechanism: by value
Conversion option specifier. The options argument is the address
of a longword bit mask in which each option bit set causes the
corresponding option to be used during the conversion. Provide
a zero (0) value to the options argument to select default
behavior or choose one or more options (status condition option,
rounding options, "FORCE" options, CRAY and IBM options) from
the following tables. Specify only the options that apply to your
conversion. A conflicting or incompatible options argument is
reported as an error (CVT$M_INVALID_OPTION).
Applicable
ConversioOption Description
Status Condition Option
All CVT$M_REPORT_ALL Report all applicable status
conditions as the default. The
reporting of recoverable status
conditions is disabled by default
when this option is not used.
Rounding Options
All CVT$M_ROUND_TO_ The default rounding option for
NEAREST conversions to IEEE data types.
This IEEE Std. 754 rounding mode
results in the representable
output value nearest to the
infinitely precise result. If the
two nearest representable values
are equally near, the one whose
least significant bit is 0 is the
result.
All CVT$M_BIASED_ The default rounding option for
ROUNDING conversions to non-IEEE data
types. Performs "traditional"
style rounding. This mode results
in the representable output
value nearest to the infinitely
precise result. If the two nearest
representable values are equally
near, the output value is the
closest to either positive
infinity or negative infinity
depending on the sign of the input
value.
All CVT$M_ROUND_TO_ZERO Round the output value toward zero
(truncate).
All CVT$M_ROUND_TO_POS Round the output value toward
positive infinity.
All CVT$M_ROUND_TO_NEG Round the output value toward
negative infinity.
"FORCE" Options
All CVT$M_FORCE_ALL_ Apply all applicable "FORCE"
SPECIAL_VALUES options for the current
conversion.
IEEE CVT$M_FORCE_DENORM_ Force a denormalized IEEE output
TO_ZERO value to zero.
IEEE CVT$M_FORCE_INF_TO_ Force a positive IEEE infinite
MAX_FLOAT output value to +max_float and
force a negative IEEE infinite
output value to -max_float.
IEEE CVT$M_FORCE_ Force an invalid IEEE NaN (not a
or VAX INVALID_TO_ZERO number) output value or a VAX ROP
(reserved operand) output value to
zero.
CRAY Format Conversion Options
CRAY CVT$M_ALLOW_OVRFLW_ Allow an input/output exponent
RANGE_VALUES value > 60000 (8).
CRAY CVT$M_ALLOW_UDRFLW_ Allow an input/output exponent
RANGE_VALUES value < 20000 (8).
IBM Format Conversion Option
IBM CVT$M_ALLOW_ Allow unnormalized input
UNNORMALIZED_VALUES arguments. Allow an unnormalized
output value for a small value
that would normalize to zero.
The maximum representable floating-point values (max_float) for
the IEEE_S_Floating, IEEE_T_Floating, IEEE_X_Floating, Big_
Endian_IEEE_S_Floating, Big_Endian_IEEE_T_Floating, and Big_
Endian_IEEE_X_Floating formats are:
Data
Type Value for: max_float
S Decimal: 3.402823e38
T Decimal: 1.797693134862316e308
X Decimal: 1.189731495357231765085759326628007016196477e4932
Declarations for the options argument are in the $CVTDEF module
found in the system symbol libraries.