.\" gd_alter_bit.3.  The gd_alter_bit man page.
.\"
.\" Copyright (C) 2008, 2009, 2010 D. V. Wiebe
.\"
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.\"
.\" This file is part of the GetData project.
.\"
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.\" under the terms of the GNU Free Documentation License, Version 1.2 or
.\" any later version published by the Free Software Foundation; with no
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.\" Texts.  A copy of the license is included in the `COPYING.DOC' file
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.\"
.TH gd_alter_bit 3 "3 November 2010" "Version 0.7.0" "GETDATA"
.SH NAME
gd_alter_bit, gd_alter_carray, gd_alter_clincom, gd_alter_const,
gd_alter_cpolynom, gd_alter_crecip, gd_alter_divide, gd_alter_lincom,
gd_alter_linterp, gd_alter_multiply, gd_alter_phase, gd_alter_polynom,
gd_alter_raw, gd_alter_recip, gd_alter_sbit
\(em modify a field in a dirfile
.SH SYNOPSIS
.B #include <getdata.h>
.HP
.nh
.ad l
.BI "int gd_alter_bit(DIRFILE *" dirfile ", const char *" field_code ,
.BI "const char *" in_field ", gd_bit_t " bitnum ", gd_bit_t " numbits );
.HP
.BI "int gd_alter_carray(DIRFILE *" dirfile ", const char *" field_code ,
.BI "gd_type_t " const_type ", size_t " array_len );
.HP
.BI "int gd_alter_clincom(DIRFILE *" dirfile ", const char *" field_code ,
.BI "int " n_fields ", const char **" in_fields ", const double complex *" cm ,
.BI "const double complex *" cb );
.HP
.BI "int gd_alter_const(DIRFILE *" dirfile ", const char *" field_code ,
.BI "gd_type_t " const_type );
.HP
.BI "int gd_alter_cpolynom(DIRFILE *" dirfile ", const char *" field_code ,
.BI "int " poly_ord ", const char *" in_field ", const double complex *" ca );
.HP
.BI "int gd_alter_crecip(DIRFILE *" dirfile ", const char *" field_code ,
.BI "const char *" in_field ", complex double " cdividend );
.HP
.BI "int gd_alter_divide(DIRFILE *" dirfile ", const char *" field_code ,
.BI "const char *" in_field1 ", const char *" in_field2 );
.HP
.BI "int gd_alter_lincom(DIRFILE *" dirfile ", const char *" field_code ,
.BI "int " n_fields ", const char **" in_fields ", const double *" m ,
.BI "const double *" b );
.HP
.BI "int gd_alter_linterp(DIRFILE *" dirfile ", const char *" field_code ,
.BI "const char *" in_field ", const char *" table ", int " rename_table );
.HP
.BI "int gd_alter_multiply(DIRFILE *" dirfile ", const char *" field_code ,
.BI "const char *" in_field1 ", const char *" in_field2 );
.HP
.BI "int gd_alter_phase(DIRFILE *" dirfile ", const char *" field_code ,
.BI "const char *" in_field ", gd_shift_t " shift );
.HP
.BI "int gd_alter_polynom(DIRFILE *" dirfile ", const char *" field_code ,
.BI "int " poly_ord ", const char *" in_field ", const double *" ca );
.HP
.BI "int gd_alter_raw(DIRFILE *" dirfile ", const char *" field_code ,
.BI "gd_type_t " data_type ", gd_spf_t " spf ", int " recode );
.HP
.BI "int gd_alter_recip(DIRFILE *" dirfile ", const char *" field_code ,
.BI "const char *" in_field ", double " dividend );
.HP
.BI "int gd_alter_sbit(DIRFILE *" dirfile ", const char *" field_code ,
.BI "const char *" in_field ", gd_bit_t " bitnum ", gd_bit_t " numbits );
.hy
.ad n
.SH DESCRIPTION
These functions provide alternatives to using the
.BR gd_alter_entry (3)
function to modify a field of the indicated type in the dirfile specified by
.IR dirfile .
.PP
In all of these calls,
.I 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
.BR get_entry (3)
and
.BR dirfile-format (5)
manual pages.  The
.B gd_bit_t
type is a signed 16-bit integer type.  The
.B gd_shift_t
type is a signed 64-bit integer type.  The
.B gd_spf_t
type is an unsigned 16-bit integer type.

The
.BR gd_alter_clincom ()
and
.BR gd_alter_cpolynom ()
functions are identical to
.BR gd_alter_lincom ()
and
.BR gd_alter_polynom (),
except they take complex scalar parameters, instead of purely real values.  This
only matters for the input of
.I 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
.BR gd_alter_lincom ()
and
.BR gd_alter_clincom ()
functions take pointers to three arrays of length
.I n_fields
containing the input field names
.RI ( in_fields ),
the gain factors
.RI ( m " or " cm ),
and the offset terms
.RI ( b " or " cb ).
Similarly,
.BR gd_alter_polynom ()
and
.BR gd_alter_cpolynom ()
take an array of length
.I poly_ord
+ 1
containing the polynomial co-efficients
.RI ( a " or " ca ).

Some field parameters have special values which indicate no change should be
made to the parameter.  Specifically, if any of the string parameters or 
.IR m ,\~ b ", or " a
.RI ( cm ,\~ cb ", or " ca )
are NULL, the old values will be retained.  Similarly, if
.IR spf ,\~ n_fields ,\~ numbits ,\~ cdividend ,
or
.I dividend
is zero, or if
.IR bitnum
is -1, or if
.IR data_type ", or " const_type
are equal to
.BR GD_NULL , 
these parameters will not be modified.

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
.BR gd_alter_entry (3),
.BR gd_alter_spec (3)
or
.BR gd_malter_spec (3),
as appropriate.

If
.I rename_table
is non-zero, the look-up table referenced by the
.B LINTERP
field will be renamed to the path given by
.IR table .
If
.I recode
is non-zero, the binary file associated with the
.B RAW
field will be re-encoded to reflect the new field parameters.

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

.SH 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:

.TP 8
.B GD_E_ACCMODE
The specified dirfile was opened read-only.
.TP
.B GD_E_ALLOC
The library was unable to allocate memory.
.TP
.B GD_E_BAD_CODE
The field specified by
.I field_code
was not found.
.TP
.B GD_E_BAD_DIRFILE
The supplied dirfile was invalid.
.TP
.B GD_E_BAD_ENTRY
One or more of the field parameters specified was invalid.
.TP
.B GD_E_BAD_FIELD_TYPE
The field specified by
.I field_code
was of the wrong type for the function called.
.TP
.B GD_E_BAD_TYPE
The
.IR data_type " or " const_type
argument was invalid.
.TP
.B GD_E_PROTECTED
The metadata of the fragment was protected from change.  Or, a request to
translate the binary file associated with a
.B RAW
field was attempted, but the data of the fragment was protected.
.TP
.B GD_E_RAW_IO
An I/O error occurred while translating the binary file associated with a
modified
.B RAW
field, or an I/O error occurred while attempting to rename a
.B LINTERP
table file.
.TP
.B 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
.B RAW
field.
.TP
.B GD_E_UNSUPPORTED
The encoding scheme of the indicated format specification fragment does not
support translating the binary file associated with a modified
.B RAW
field.
.PP
The dirfile error may be retrieved by calling
.BR gd_error (3).
A descriptive error string for the last error encountered can be obtained from
a call to
.BR gd_error_string (3).

.SH NOTES
The C89 GetData API provides different prototypes for
.BR gd_alter_clincom (),\~ gd_alter_cpolynom (),
and
.BR gd_alter_crecip ():
.PP
.nf
.B #define GD_C89_API
.B #include <getdata.h>
.HP
.nh
.ad l
.BI "int gd_alter_clincom(DIRFILE *" dirfile ", const char *" field_code ,
.BI "int " n_fields ", const char **" in_fields ", const double *" cm ,
.BI "const double *" cb );
.HP
.BI "int gd_alter_cpolynom(DIRFILE *" dirfile ", const char *" field_code ,
.BI "int " poly_ord ", const char *" in_fields ", const double *" ca );
.HP
.BI "int gd_alter_crecip(DIRFILE *" dirfile ", const char *" field_code ,
.BI "const char *" in_field ", double " cdividend [2]);
.hy
.ad n
.fi
.PP
In this case, the array pointers passed as
.IR cm ,\~ cb
or
.IR ca
should have twice as many (purely real) elements, consisting of alternating
real and imaginary parts for the complex data.  For example,
.IR ca [0]
should be the real part of the first co-efficient,
.IR ca [1]
the imaginary part of the first co-efficient,
.IR ca [2]
the real part of the second co-efficient,
.IR ca [3]
the imaginary part of the second co-efficient, and so on.  Similarly, the
.I cdividend
parameter becomes a double precision array of length two.

.SH SEE ALSO
.BR gd_alter_entry (3),
.BR gd_alter_spec (3),
.BR gd_error (3),
.BR gd_error_string (3),
.BR gd_malter_spec (3),
.BR gd_metaflush (3),
.BR gd_open (3),
.BR dirfile-format (5)