gd_alter_bit(3) gd_alter_const,

SYNOPSIS

#include <getdata.h>
int gd_alter_bit(DIRFILE *dirfile, const char *field_code, const char *in_field, int bitnum, int numbits);
int gd_alter_carray(DIRFILE *dirfile, const char *field_code, gd_type_t const_type, size_t array_len);
int gd_alter_clincom(DIRFILE *dirfile, const char *field_code, int n_fields, const char **in_fields, const double complex *cm, const double complex *cb);
int gd_alter_const(DIRFILE *dirfile, const char *field_code, gd_type_t const_type);
int gd_alter_cpolynom(DIRFILE *dirfile, const char *field_code, int poly_ord, const char *in_field, const double complex *ca);
int gd_alter_crecip(DIRFILE *dirfile, const char *field_code, const char *in_field, complex double cdividend);
int gd_alter_divide(DIRFILE *dirfile, const char *field_code, const char *in_field1, const char *in_field2);
int gd_alter_lincom(DIRFILE *dirfile, const char *field_code, int n_fields, const char **in_fields, const double *m, const double *b);
int gd_alter_linterp(DIRFILE *dirfile, const char *field_code, const char *in_field, const char *table, int rename_table);
int gd_alter_mplex(DIRFILE *dirfile, const char *field_name, const char *in_field, const char *count_field, int count_val, int period);
int gd_alter_multiply(DIRFILE *dirfile, const char *field_code, const char *in_field1, const char *in_field2);
int gd_alter_phase(DIRFILE *dirfile, const char *field_code, const char *in_field, gd_shift_t shift);
int gd_alter_polynom(DIRFILE *dirfile, const char *field_code, int poly_ord, const char *in_field, const double *ca);
int gd_alter_raw(DIRFILE *dirfile, const char *field_code, gd_type_t data_type, unsigned int spf, int recode);
int gd_alter_recip(DIRFILE *dirfile, const char *field_code, const char *in_field, double dividend);
int gd_alter_sbit(DIRFILE *dirfile, const char *field_code, const char *in_field, int bitnum, int numbits);
int gd_alter_window(DIRFILE *dirfile, const char *field_code, const char *in_field, const char *check_field, gd_windop_t windop, gd_triplet_t threshold);

DESCRIPTION

These functions provide alternatives to using the gd_alter_entry(3) function to modify a field of the indicated type in the dirfile specified by dirfile.

In all of these calls, field_code indicates the the field to be modified, which may be a regular field, or a metafield specified by its full (slashed) field code, but should not contain a representation suffix. The meaning and valid types of other arguments may be obtained from the get_entry(3) and dirfile-format(5) manual pages. The gd_shift_t type is a signed 64-bit integer type. The gd_triplet_t type is defined as: 

typedef union {
  gd_int64_t i;
  gd_uint64_t u;
  double r;
} gd_triplet_t;

Which element of this gd_triplet_t union to set depends on the operator selected for the WINDOW field. See gd_entry(3) for details.

The gd_alter_clincom() and gd_alter_cpolynom() functions are identical to gd_alter_lincom() and gd_alter_polynom(), except they take complex scalar parameters, instead of purely real values. This only matters for the input of new parameters; if the scalar parameters are not changed (by passing NULL instead of a list of scalars), the functions can be used interchangeably, regardless of whether the altered field has complex scalar parameters or not.

If the corresponding parameters are to be changed, the gd_alter_lincom() and gd_alter_clincom() functions take pointers to three arrays of length n_fields containing the input field names (in_fields), the gain factors (m or cm), and the offset terms (b or cb). Similarly, gd_alter_polynom() and gd_alter_cpolynom() take an array of length poly_ord + 1 containing the polynomial co-efficients (a or ca).

Some field parameters have special values which indicate no change should be made to the parameter. These special values are:

NULL:
any of the string parameters, also m, b, a, cm, cb, or ca;
0:
spf, n_fields, numbits, cdividend, dividend, or array_len;
-1:
bitnum or period;
GD_NULL:
data_type or const_type;
GD_WINDOP_UNK:
windop.

All field parameters introduced with this interface must contain literal parameters. Field parameters which are scalar fields cannot be introduced with these functions. To do that, use gd_alter_entry(3), gd_alter_spec(3) or gd_malter_spec(3), as appropriate.

If rename_table is non-zero, the look-up table referenced by the LINTERP field will be renamed to the path given by table. If recode is non-zero, the binary file associated with the RAW field will be re-encoded to reflect the new field parameters. In this case, the field's I/O pointer will be reset to the beginning-of-frame.

If gd_alter_carray() is used to increase the length of a CARRAY field, the added elements will be uninitialised. Use gd_put_carray_slice(3) or equivalent to initialise them.

See NOTES below for information on using gd_alter_clincom(), gd_alter_crecip(), and gd_alter_cpolynom() in the C89 GetData API.

RETURN VALUE

On success, any of these functions returns zero. On error, -1 is returned and the dirfile error is set to a non-zero error value. Possible error values are:

GD_E_ACCMODE
The specified dirfile was opened read-only.
GD_E_ALLOC
The library was unable to allocate memory.
GD_E_BAD_CODE
The field specified by field_code was not found, or a supplied field code did not contain the appropriate prefix or suffix.
GD_E_BAD_DIRFILE
The supplied dirfile was invalid.
GD_E_BAD_ENTRY
One or more of the field parameters specified was invalid.
GD_E_BAD_FIELD_TYPE
The field specified by field_code was of the wrong type for the function called.
GD_E_BAD_TYPE
The data_type or const_type argument was invalid.
GD_E_IO
An I/O error occurred while translating the binary file associated with a modified RAW field, or an I/O error occurred while attempting to rename a LINTERP table file.
GD_E_PROTECTED
The metadata of the fragment was protected from change. Or, a request to translate the binary file associated with a RAW field was attempted, but the data of the fragment was protected.
GD_E_UNKNOWN_ENCODING
The encoding scheme of the indicated format specification fragment is not known to the library. As a result, the library was unable to translate the binary file be associated with a modified RAW field.
GD_E_UNSUPPORTED
The encoding scheme of the indicated format specification fragment does not support translating the binary file associated with a modified RAW field.

The dirfile error may be retrieved by calling gd_error(3). A descriptive error string for the last error encountered can be obtained from a call to gd_error_string(3).

NOTES

The C89 GetData API provides different prototypes for gd_alter_clincom(), gd_alter_cpolynom(), and gd_alter_crecip(): 

#define GD_C89_API


#include <getdata.h>
int gd_alter_clincom(DIRFILE *dirfile, const char *field_code, int n_fields, const char **in_fields, const double *cm, const double *cb);
int gd_alter_cpolynom(DIRFILE *dirfile, const char *field_code, int poly_ord, const char *in_fields, const double *ca);
int gd_alter_crecip(DIRFILE *dirfile, const char *field_code, const char *in_field, const double cdividend[2]);

In this case, the array pointers passed as cm, cb or ca should have twice as many (purely real) elements, consisting of alternating real and imaginary parts for the complex data. That is, for example, ca[0] should be the real part of the first co-efficient, ca[1] the imaginary part of the first co-efficient, ca[2] the real part of the second co-efficient, ca[3] the imaginary part of the second co-efficient, and so on. Similarly, the cdividend parameter becomes a double precision array of length two.

For gd_alter_clincom() and gd_alter_cpolynom(), these are simply different (but equivalent) declarations of the C99 function entry point. For gd_alter_crecip(), however, a different entry point is needed (since the cdividend parameter is passed by reference instead of by value). In the interests of portability, the C89 version of gd_alter_crecip() is always available, and may be accessed as gd_alter_crecip89(), with the C89 prototype, in both the C99 and C89 APIs. Passing NULL as cdividend is equivalent to specifying a dividend of zero: it indicates no change to the dividend parameter.

SEE ALSO

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