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NAME
convert_external - convert external binary data formats
SYNOPSIS
cc [ flag ... ] file ... -lsunmath -lm [ library ... ]
#include <sunmath.h>
enum convert_external_arch_t = {
convert_external_sparc, convert_external_pc,
convert_external_vax, convert_external_vaxg,
convert_external_s370, convert_external_cray };
enum convert_external_type_t = {
convert_external_signed,
convert_external_unsigned,
convert_external_float };
enum convert_external_rounding_t = {
convert_external_common = -1,
convert_external_biased = -2,
convert_external_away = -3 };
typedef struct {
enum convert_external_arch_t arch ; /* format architecture */
enum convert_external_type_t type ; /* format type */
int size ; /* format size in 8-bit bytes */
} convert_external_t ;
fp_exception_field_type convert_external(const char *src_p,
convert_external_t src_format, char *dst_p,
convert_external_t dst_format, int rounding, int n);
fp_exception_field_type convert_external_(const char *src_p,
const convert_external_t *src_format_p, char *dst_p, const
convert_external_t *dst_format_p, const int *rounding_p,
const int *n_p);
DESCRIPTION
convert_external() is used in C programs to convert between
binary data on non-SPARC systems and SPARC binary data. The
data may be signed integers, unsigned integers, or
floating-point data. convert_external_() is used in FORTRAN
programs (CALL CONVERT_EXTERNAL(...)) for the same purpose,
with all parameters call-by-reference.
The convert_external_t type describes the supported formats;
for each architecture, signed and unsigned integers of sizes
1, 2, 4, 8, or 16 bytes, and floating-point types of sizes
4, 8, 10, 12, or 16 bytes in size are supported. If an
improper size is specified for the source or destination, no
conversion occurs and (1<<fp_division) is returned, an
exception that can't arise otherwise.
Supported architectures and formats include
external_t endian- float*4 float*8 float*10 float*12 float*16
architecture ness format format format format format
sparc big IEEE IEEE none MC68881 IEEE
single double extended quad
pc little IEEE IEEE i80x87 i80960KB IEEE
single double extended extended quad
vax little VAX F VAX D none none VAX H
vaxg little VAX F VAX G none none VAX H
s370 big S/370 S/370 none none S/370
single double extended
cray big none Cray-1 none none Cray-1
single double
Note that MC68000 and SPARC formats are identical big-endian
formats; the Intel PC formats for 8086/8087, 80x86/7, and
80486 are identical little-endian. Table entries ``none''
represent improper sizes; no conversion occurs. ``IEEE
quad'' refers to the natural big- or little-endian extension
of IEEE single and double precision to a format with 15
exponent bits, one implicit significand bit, and 112 expli-
cit significand bits.
USAGE
excep = convert_external(src_p, src_format, dst_p, dst_format, rounding, n);
excep
The function value is an accumulation of all the
exceptions encountered during the conversion. If
detecting individual exceptions is important, n
should be 1 so that only one data item is con-
verted at a time.
src_p
A pointer to the data to be converted stored as a
contiguous array. The pointer is declared char *
to emphasize that there are no alignment require-
ments, although data being converted to SPARC for-
mat for subsequent processing by the same program
should be appropriately aligned.
dst_p
A pointer to the converted data stored as a con-
tiguous array.
src_format
Description of the format of the source data.
dst_format
Description of the format of the destination data.
rounding
The rounding mode to apply to the destination
data.
n Number of data items to be converted.
Rounding choices; the first is intended to be satisfactory
for almost all applications:
(int) convert_external_common
integer and unsigned destination formats round toward
zero (2.9 rounds to 2, -2.9 rounds to -2),
IEEE floating-point destinations round to nearest
unbiased,
VAX floating-point destinations round to nearest
biased,
IBM 370 and Cray floating-point destinations round
toward zero.
(int) convert_external_biased
to round to nearest biased (for integer destinations,
1.5 rounds to 2, 2.5 rounds to 3).
(int) convert_external_away
to round away from zero (for integer destinations, 2.1
rounds to 3, -2.1 rounds to -3).
(int) fp_nearest, fp_tozero, fp_positive, fp_negative
to obtain rounding in one of the modes specified in
IEEE 754.
After the conversion, if (excep & (1 << fp_invalid)) != 0,
then one or more invalid exceptions occurred; similarly for
the other exceptions, which are defined this way:
fp_invalid
An input argument was an IEEE signaling NaN or a VAX
reserved operand, or an input argument was an infinity
and the destination was an integer or unsigned type, or
a floating-point type with no infinity representation.
fp_overflow
An input argument was finite and large but could not be
represented in the destination format with only normal
rounding error; if the destination format is integer or
unsigned then fp_overflow represents integer overflow.
fp_underflow
An input argument was finite and small and could not be
represented in the destination format with only normal
rounding error. This can only arise with floating-
point destinations.
fp_inexact
An input argument was finite but could not be
represented exactly in the destination format.
fp_division
The source or destination formats aren't supported. No
conversions are done.
Note that converting external data to SPARC format, process-
ing on a SPARC, then converting back to external format will
almost never yield the same results as processing the data
entirely on the external system, even if the conversions and
processing yield no exceptions on the SPARC.
EXAMPLES
Generating data on an external system
The following code demonstrates typical FORTRAN generation
of binary floating-point data on an external system:
REAL A(100)
WRITE(9) A
Converting external data to SPARC internal form in C
Suppose the previous binary data file was created on a tape
on a Cray and read on a SPARC system. To convert to IEEE
double-precision floating-point format, but using biased
rounding,
#include <sunmath.h>
char datasrc[800];
double datadest[100];
fp_exception_field_type excep;
int rounding;
int i;
convert_external_t src, dest;
/* read the Cray data into the array datasrc somehow, then ... */
src.arch = convert_external_cray;
src.type = convert_external_float;
src.size = 8;
dest.arch = convert_external_sparc;
dest.type = convert_external_float;
dest.size = 8;
rounding = convert_external_biased;
excep = convert_external((char *) datasrc, src, (char *) datadest, dest, rounding, 100);
/*
* usually you aren't interested in inexact exceptions
* and you'd do this
*/
excep &= ~(1 << fp_inexact);
/*
* other exceptions are possible in this example - after the fact,
* you can find out where they happened this way
*/
if (excep != 0) for (i = 0 ; i < 100 ; i++) {
excep = convert_external((char *)&datasrc[8 * i], src, (char *)&datadest[i], dest, rounding, 1);
if (excep != 0) {
/* do something specific about datadest[i] */
}
}
Converting SPARC internal data to external form in FORTRAN
Suppose data created in a SPARC program is to be read into
an IBM PC. To convert,
#include <f77_floatingpoint.h>
REAL*4 datasrc(100)
REAL*4 datadest(100)
INTEGER excep, convert_external, round
INTEGER src(4), dest(4)
c create datasrc array somehow, then ...
src(1) = convert_external_sparc
src(2) = convert_external_float
src(3) = 4
dest(1) = convert_external_pc
dest(2) = convert_external_float
dest(3) = 4
round = convert_external_common
excep = convert_external(datasrc, src, datadest, dest, round, 100)
c The only exception that can arise is fp_invalid,
c by converting a signaling NaN.
c Now write the data out in a file that an IBM PC can read
SEE ALSO
dd(1M), for reading tapes from foreign systems; xdr(3N), for
formatting arbitrary data structures in a machine-
independent fashion.
NOTES
Conversions are performed one at a time by converting a
source datum into an internal format large enough to hold
any input exactly, then by converting the internal data to
the destination form. Thus any pair of source and destina-
tion formats is permitted, but efficiency is not as high as
would be the case for programs written to convert from one
specific format to another.
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