cvt_ftof(3)cvt_ftof(3)NAMEcvt_ftof - Converts a floating-point data type to another supported
floating-point data type.
SYNOPSIS
#include <cvt.h>
int cvt_ftof(
void *input_val,
int input_type,
void *output_val,
int output_type,
int options );
LIBRARY
Math Library (libm)
DESCRIPTIONcvt_ftof() converts one floating-point data type to another.
Input_val points to the input value to be converted and output_val
points to the converted result. The conversion is subject to the
options specified in the options (bit field) argument. This function
returns a bit field indicating any status conditions.
Input_type and output_type identify the floating-point data type of
input_val and output_val as follows:
────────────────────────────────────────────────────────────
Input_type/Output_type Data Type Size
────────────────────────────────────────────────────────────
CVT_VAX_F VAX F Floating 4 bytes
CVT_VAX_D VAX D Floating 8 bytes
CVT_VAX_G VAX G Floating 8 bytes
CVT_VAX_H VAX H Floating 16 bytes
CVT_IEEE_S IEEE Little Endian S 4 bytes
Floating
CVT_IEEE_T IEEE Little Endian T 8 bytes
Floating
CVT_IEEE_X IEEE Little Endian X 16 bytes
Floating
CVT_BIG_ENDIAN_IEEE_S IEEE Big Endian S 4 bytes
Floating
CVT_BIG_ENDIAN_IEEE_T IEEE Big Endian T 8 bytes
Floating
CVT_BIG_ENDIAN_IEEE_X IEEE Big Endian X 16 bytes
Floating
CVT_IBM_SHORT IBM Short Floating 4 bytes
CVT_IBM_LONG IBM Long Floating 8 bytes
CVT_CRAY_SINGLE Cray Single Floating 8 bytes
────────────────────────────────────────────────────────────
Provide a zero (0) value to the options argument to select default
behavior or choose one or more options (status condition option, round‐
ing options, "FORCE" options, Cray and IBM options) from the tables
below as the options argument. Specify only the options that apply to
your conversion. A conflicting or incompatible options argument will be
reported as an error (CVT_INVALID_OPTION).
────────────────────────────────────────────────────────────────────────────
Applicable Status Condition Option Description
Conversion
────────────────────────────────────────────────────────────────────────────
All CVT_REPORT_ALL Report all applicable status con‐
ditions as the default. The
reporting of recoverable status
conditions is disabled by default
when this option is not used.
All CVT_ROUND_TO_NEAREST The default rounding mode for
conversions to IEEE data types.
This IEEE Std. 754 rounding mode
results in a representable output
value nearest to the infinitely
precise result. If the two near‐
est representable values are
equally near, the one with its
least significant bit zero is the
result.
All CVT_BIASED_ROUNDING The default rounding mode for
conversions to non-IEEE data
types. Performs "traditional"
style rounding. This mode
results in a representable output
value nearest to the infinitely
precise result. If the two near‐
est 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_ROUND_TO_ZERO Round the output value toward
zero (truncate).
All CVT_ROUND_TO_POS Round the output value toward
positive infinity.
All CVT_ROUND_TO_NEG Round the output value toward
negative infinity.
────────────────────────────────────────────────────────────────────────────
────────────────────────────────────────────────────────────────────────────
Applicable "FORCE" Options Description
Conversion
────────────────────────────────────────────────────────────────────────────
All CVT_FORCE_ALL_SPECIAL_VALUES Apply all applicable "FORCE"
options for the current con‐
version.
IEEE CVT_FORCE_DENORM_TO_ZERO Force a denormalized IEEE out‐
put value to zero. This option
is valid only for conversions
to IEEE output values.
IEEE CVT_FORCE_INF_TO_MAX_FLOAT Force a positive IEEE infinite
output value to +max_float and
force a negative IEEE infinite
output value to -max_float.
This option is valid only for
conversions to IEEE output
values.
IEEE or VAX CVT_FORCE_INVALID_TO_ZERO Force an invalid IEEE NaN (not
a number) output value or a
VAX ROP (reserved operand)
output value to zero. This
option is valid only for con‐
versions to IEEE or VAX output
values.
────────────────────────────────────────────────────────────────────────────
────────────────────────────────────────────────────────────────────────────
Applicable Options for Cray Format Conver‐ Description
Conversion sion
────────────────────────────────────────────────────────────────────────────
Cray CVT_ALLOW_OVRFLW_RANGE_VALUES Allow an input/output
exponent value > 60000
(8).
Cray CVT_ALLOW_UDRFLW_RANGE_VALUES Allow an input/output
exponent value < 20000
(8).
────────────────────────────────────────────────────────────────────────────
────────────────────────────────────────────────────────────────────────────
Applicable Options for IBM Format Con‐ Description
Conversion version
────────────────────────────────────────────────────────────────────────────
IBM CVT_ALLOW_UNNORMALIZED_VALUES Allow unnormalized input
arguments. Allow an unnor‐
malized output value for a
small value which would nor‐
malize 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 max_float Value
────────────────────────────────────────────────────────────────────
S_FLOAT Decimal: 3.402823e38
T_FLOAT Decimal: 1.797693134862316e308
X_FLOAT Decimal:
1.189731495357231765085759326628007016196477e4932
────────────────────────────────────────────────────────────────────
RETURN VALUES
The return value is a bit field containing the condition codes raised
by the function. cvt_ftof() returns CVT_NORMAL; otherwise, it sets one
or more of the following recoverable and unrecoverable conditions. Use
the following condition names to determine which conditions are set:
───────────────────────────────────────────────────────────────
Condition Name Condition (Always reported by
default)
───────────────────────────────────────────────────────────────
CVT_INVALID_INPUT_TYPE Invalid input type code.
CVT_INVALID_OUTPUT_TYPE Invalid output type code.
CVT_INVALID_OPTION Invalid option argument.
───────────────────────────────────────────────────────────────
──────────────────────────────────────────────────────────────────
Condition Name Condition (Only reported if the
CVT_REPORT_ALL option is selected)
──────────────────────────────────────────────────────────────────
CVT_RESULT_INFINITE Conversion produced an infinite
result. (For conversions to IEEE
data types.)
CVT_RESULT_DENORMALIZED Conversion produced a denormalized
result. (For conversions to IEEE
data types.)
CVT_RESULT_OVERFLOW_RANGE Conversion yielded an exponent >
60000 (8). (For Cray data type con‐
versions.)
CVT_RESULT_UNDERFLOW_RANGE Conversion yielded an exponent <
20000 (8). (For Cray data type con‐
versions.)
CVT_RESULT_UNNORMALIZED Conversion produced an unnormalized
result. (For IBM data type conver‐
sions and reported
CVT_RESULT_INVALID Conversion result is either ROP
(reserved operand), NaN (not a num‐
ber), or closest equivalent. Cray
and IBM data types return 0. (For
all data type conversions.)
CVT_RESULT_OVERFLOW Conversion resulted in overflow.
(For all data type conversions.)
CVT_RESULT_UNDERFLOW Conversion resulted in underflow.
(For all data type conversions.)
CVT_RESULT_INEXACT Conversion resulted in a loss of
precision. (For all data type con‐
versions.)
──────────────────────────────────────────────────────────────────
EXAMPLES
This example converts the value pointed to by big_x which is of type
IEEE Big Endian T Floating, to the IEEE Little Endian T Floating
data type and stores the result in the location pointed to by little_x.
No conversion options are specified.
status = cvt_ftof( &big_x, CVT_BIG_ENDIAN_IEEE_T,
&little_x, CVT_IEEE_T, 0 );
This example converts the value pointed to by x which is of type VAX D
Floating, to the IEEE Little Endian T Floating data type and stores
the result in the location pointed to by y. Any special IEEE values
which would normally be generated will be removed. That is,
NaN and Denormalized results will be returned as zero and infinite
results will go to +- max_float. In addition, all recordable status
conditions will be reported.
status = cvt_ftof(&x, CVT_VAX_D, &y, CVT_IEEE_T,
(CVT_FORCE_ALL_SPECIAL_VALUES | CVT_REPORT_ALL) );
SEE ALSO
ANSII/IEEE Std 754-1985, IEEE Standard for Binary Floating-Point Arith‐
metic
cvt_ftof(3)
