man gd_entry (3): retrieve a dirfile field's metadata

SYNOPSIS

#include <getdata.h>

int gd_entry(DIRFILE *dirfile, const char *field_code, gd_entry_t *entry);

DESCRIPTION

The gd_entry() function queries a dirfile(5) database specified by dirfile and returns the metadata associated with the field specified by field_code. If field_code contains a valid representation suffix, the suffix will be ignored.

The dirfile argument must point to a valid DIRFILE object previously created by a call to gd_open(3).

The entry will be stored in the gd_entry_t structure indicated by the entry argument, which must be allocated by the caller. Members available in this structure depend on the field type of the field queried. See below for a complete description of this data type.

Strings members in entry filled by this function (variously, depending on field type: field, the elements of the in_fields[] array, table; see below) will by dynamically allocated by gd_entry() and should not point to allocated memory locations before calling this function. Only strings provided by the gd_entry_t for the particular field type described will be allocated. These strings should be de-allocated with free(3) by the caller once they are no longer needed. The gd_free_entry_strings(3) function is provided as a convenience to do this.

If the entry's metadata contains scalar field codes which cannot be dereferenced, the associated numerical field parameter will be initialised to zero. In this case, the GD_EN_CALC flag in the returned entry object will NOT be set.

The returned entry structure, including strings and their pointers may be freely modified by the caller.

RETURN VALUE

Upon successful completion, gd_entry() returns zero, and writes the field metadata in the supplied gd_entry_t buffer. On error, the supplied gd_entry_t buffer is not modified. In this case, gd_entry() returns -1 and sets the dirfile error to a non-zero error value. Possible error values are:

GD_E_ALLOC: The library was unable to allocate memory.
GD_E_BAD_CODE: The field specified by field_code was not found in the database.
GD_E_BAD_DIRFILE: The supplied dirfile was invalid.

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).

THE ENTRY TYPE

Members available in the gd_entry_t structure depend on the field type described. All gd_entry_t objects are guaranteed to have at least:

typedef struct {
  ...
  const char  *field;          /* field code */
  gd_entype_t  field_type;     /* field type */
  int          fragment_index; /* format fragment index */
  unsigned     flags;          /* entry flags */
  ...
} gd_entry_t;

The field member is the field code of the entry (i.e. its string name). If the call to gd_entry(3) is successful, this will be the field name specified as part of the field_code argument.

The field_type member indicates the field type of the entry. This is an integer type equal to one of the following symbols:

: GD_BIT_ENTRY, GD_CARRAY_ENTRY, GD_CONST_ENTRY, GD_DIVIDE_ENTRY, GD_INDEX_ENTRY, GD_LINCOM_ENTRY, GD_LINTERP_ENTRY, GD_MPLEX_ENTRY, GD_MULTIPLY_ENTRY, GD_PHASE_ENTRY, GD_POLYNOM_ENTRY, GD_RAW_ENTRY, GD_RECIP_ENTRY, GD_SBIT_ENTRY, GD_STRING_ENTRY, GD_WINDOW_ENTRY.

GD_INDEX_ENTRY is a special field type used only for the implicit INDEX field. The other entry types are explained in detail in dirfile-format(5).

The fragment_index member indicates the format specification fragment in which this field is defined. This is an integer index to the Dirfile's list of parsed format specification fragments. The name of the file corresponding to fragment_index may be obtained by calling gd_fragmentname(3). A value of zero for this field indicates that the field is defined in the primary fragment, the file called format in the root dirfile directory (see dirfile(5)).

The flags member is a bitwise or'd collection of the following entry flags:

GD_EN_CALC: This bit is set only when the non-literal scalar parameter field codes specified in the scalar member have been resolved, and the corresponding numerical parameter have been initialised with these data. When one or more field code does not exist, or is invalid (ie. when gd_validate(3) would fail on the specified field_code with the error GD_E_BAD_SCALAR), then the unresolved numerical parameters are initialised to zero, and this flag is not be set. If the requested field does not allow non-literal scalar parameters (CARRAY, CONST, DIVIDE, INDEX, LINTERP, MULTIPLY, STRING), the value of this bit is unspecified.
GD_EN_COMPSCAL: For fields which permit complex valued parameters (LINCOM, POLYNOM, RECIP), this bit is set only when at least one parameter is complex valued. For other field types, the value of this bit is unspecified.
GD_EN_HIDDEN: This bit is set only when the field has been hidden by the /HIDDEN directive (see gd_hidden(3)).

Remaining fields in the gd_entry_t structure depend on the value of field_type. Callers are advised to check field_type before attempting to access the remaining members. Members for different field types may be stored in the same physical location in core. Accordingly, attempting to access a member not declared for the appropriate field type will have unspecified results.

Scalar Parameter Members

A gd_entry_t describing any field type which permits non-literal scalar field parameters (BIT, LINCOM, MPLEX, PHASE, POLYNOM, RAW, RECIP, SBIT, or WINDOW) will also provide:

typedef struct {
  ...
  const char *scalar[GD_MAX_POLY_ORD + 1];     /* param. fields */
  int         scalar_ind[GD_MAX_POLY_ORD + 1]; /* CARRAY indices */
  ...
} gd_entry_t;

Only certain elements of these arrays will be initialised:

For BIT and SBIT fields, the first element corresponds to bitnum and the second to numbits. The remainder are uninitialised.
For LINCOM fields, the first GD_MAX_LINCOM elements correspond to the slopes (cm) and the next GD_MAX_LINCOM elements correspond to the offsets (cb). Only the first n_fields elements of these two sets are initialised. Notably, this means for n_fields < GD_MAX_LINCOM, there will be uninitialised elements in the middle of these arrays between the element corresponding to cm[n_fields - 1] and the element corresponding to cb[0].
For MPLEX fields, the first element corresponds to count_val and the second to period. The remainder are uninitialised.
For PHASE fields, the first element corresponds to shift. The remainder are uninitialised.
For POLYNOM fields, these arrays correspond with the co-efficients ca. Only the first poly_ord + 1 elements are initialised.
For RAW fields, the first element corresponds to spf. The remainder are uninitialised.
For RECIP fields, the first element corresponds to cdividend. The remainder are uninitialised.
For WINDOW fields, the first element corresponds to threshold. The remainder are uninitialised.

The scalar parameters are NULL if a literal parameter was used, or else a field code specifying the scalar parameters.

If an element of scalar specifies a CARRAY field, the corresponding scalar_ind will indicate the element of the CARRAY used. For CONST fields, scalar_ind will be -1.

BIT and SBIT Members

A gd_entry_t describing a BIT or SBIT entry, will also provide:

typedef struct {
  ...
  const char *in_fields[1];     /* input field code */
  int         bitnum;           /* first bit */
  int         numbits;          /* bit length */
  ...
} gd_entry_t;

The in_fields member is an array of length one containing the input field code.

The bitnum member indicates the number of the first bit (counted from zero) extracted from the input. If this value was specified as a scalar field code, this will be the numerical value of that field, and scalar[0] will contain the field code itself, otherwise scalar[0] will be NULL.

The numbits member indicates the number of bits which are extracted from the input. If this value was specified as a scalar field code, this will be the numerical value of that field, and scalar[1] will contain the field code itself, otherwise scalar[1] will be NULL.

CARRAY Members

A gd_entry_t describing a CARRAY entry, will also provide:

typedef struct {
  ...
  gd_type_t   const_type;     /* data type in format specification */
  size_t      array_len;      /* length of array data */
  ...
} gd_entry_t;

The const_type member indicates the data type of the constant value stored in the format file metadata. See gd_getdata(3) for a list of valid values that a variable of type gd_type_t may take.

The array_len member gives the number of elements in the array.

CONST Members

A gd_entry_t describing a CONST entry, will also provide:

typedef struct {
  ...
  gd_type_t   const_type;     /* data type in format specification */
  ...
} gd_entry_t;

INDEX Members

A gd_entry_t describing an INDEX entry, which is used only for the implicit INDEX field, provides no additional data.

LINCOM Members

A gd_entry_t describing a LINCOM entry, will also provide:

typedef struct {
  ...
  int            n_fields;                  /* # of input fields */
  const char    *in_fields[GD_MAX_LINCOM];  /* input field code(s) */
  double complex cm[GD_MAX_LINCOM];         /* scale factor(s) */
  double         m[GD_MAX_LINCOM];          /* scale factor(s) */
  double complex cb[GD_MAX_LINCOM];         /* offset terms(s) */
  double         b[GD_MAX_LINCOM];          /* offset terms(s) */
  ...
} gd_entry_t;

The n_fields member indicates the number of input fields. It will be between one and GD_MAX_LINCOM inclusive. GD_MAX_LINCOM is defined in getdata.h as the maximum number of input fields permitted by a LINCOM.

The in_fields member is an array of length GD_MAX_LINCOM containing the input field code(s). Only the first n_fields elements of this array are initialised. The remaining elements contain uninitialised data.

The cm and cb members are arrays of the scale factor(s) and offset term(s) for the LINCOM. Only the first n_fields elements of these array contain meaningful data. If any of these values were specified as a scalar field code, this will be the numerical value of that field. The field code corresponding to cm[i] will be stored in scalar[i] and the field code associated with cb[i] will be stored in scalar[i + GD_MAX_LINCOM]. Otherwise the corresponding scalar member will be NULL. See NOTES below on changes to the declaration of cm and cb when using the C89 GetData API.

The elements of m and b are the real parts of the corresponding elements of cm and cb.

LINTERP Members

A gd_entry_t describing a LINTERP entry, will also provide:

typedef struct {
  ...
  const char *table             /* linterp table filename */
  const char *in_fields[1];     /* input field code */
  ...
} gd_entry_t;

The table member is the pathname to the look up table on disk. This the path as it appars in the format specification. It may be a path relative to the fragment directory. For an canonicalised, absolute version of this path, see gd_linterp_tablename(3).

The in_fields member is an array of length one containing the input field code.

MPLEX Members

A gd_entry_t describing a MPLEX entry, will also provide:

typedef struct {
  ...
  const char    *in_fields[2];  /* input field codes */
  int           count_val;      /* value of the multiplex index */
  int           period;         /* samples between successive count_vals */
  ...
} gd_entry_t;

The in_fields member contains the field codes of the input field (element 0) and the multiplex index field (element 1).

The count_val member is the value of the multiplex index field when the output field is stored in the input field.

The period member is the number of samples between successive occurrances of count_val in the index vector, or zero, if this is not known or constant. This is only used to determine how far to look back for a starting value for the output field; see gd_mplex_lookback(3).

MULTIPLY and DIVIDE Members

A gd_entry_t describing a MULTIPLY or DIVIDE entry, will also provide:

typedef struct {
  ...
  const char *in_fields[2];     /* input field codes */
  ...
} gd_entry_t;

The in_fields member is an array of length two containing the input field codes.

PHASE Members

A gd_entry_t describing a PHASE entry, will also provide:

typedef struct {
  ...
  const char *in_fields[1];     /* input field code */
  gd_shift_t  shift;            /* phase shift */
  ...
} gd_entry_t;

The in_fields member is an array of length one containing the input field code.

The shift member indicates the shift in samples. The gd_shift_t type is a 64-bit signed integer type. A positive value indicates a shift forward in time (towards larger frame numbers). If this value was specified as a scalar field code, this will be the numerical value of that field, and scalar[0] will contain the field code itself, otherwise scalar[0] will be NULL.

POLYNOM Members

A gd_entry_t describing a POLYNOM entry, will also provide:

typedef struct {
  ...
  int            poly_ord;                  /* polynomial order */
  const char    *in_fields[1];              /* input field code(s) */
  double complex ca[GD_MAX_POLY_ORD + 1];   /* co-efficients(s) */
  double         a[GD_MAX_POLY_ORD + 1];    /* co-efficients(s) */
  ...
} gd_entry_t;

The poly_ord member indicates the order of the polynomial. It will be between one and GD_MAX_POLY_ORD inclusive. GD_MAX_POLY_ORD is defined in getdata.h as the maximum order of polynomial permitted by a POLYNOM.

The in_fields member is an array of length one containing the input field code.

The ca members are arrays of the co-efficient(s) for the POLYNOM. Only the first poly_ord + 1 elements of this array contains meaningful data. If any of these values were specified as a scalar field code, this will be the numerical value of that field. The field code corresponding to ca[i] will be stored in scalar[i]. Otherwise the corresponding scalar member will be NULL. See NOTES below on changes to the declaration of ca when using the C89 GetData API.

The elements of a are the real parts of the corresponding elements of ca.

RAW Members

A gd_entry_t describing a RAW entry, will also provide:

typedef struct {
  ...
  unsigned int  spf;          /* samples per frame on disk */
  gd_type_t     data_type;    /* data type on disk */
  ...
} gd_entry_t;

The spf member contains the samples per frame of the binary data on disk. If this value was specified as a scalar field code, this will be the numerical value of that field, and scalar[0] will contain the field code itself, otherwise scalar[0] will be NULL.

The data_type member indicates the data type of the binary data on disk. See gd_getdata(3) for a list of valid values that a variable of type gd_type_t may take.

RECIP Members

A gd_entry_t describing a RECIP entry, will also provide:

typedef struct {
  ...
  const char    *in_fields[1];         /* input field code */
  double complex cdividend;            /* scalar dividend */
  double         dividend;             /* scalar dividend */
  ...
} gd_entry_t;

The in_fields member is an array of length one containing the input field code.

The cdividend member provides the constant dividend of the computed division. If this value was specified as a scalar field code, this will be the numerical value of that field, and scalar[0] will contain the field code itself, otherwise scalar[0] will be NULL. The dividend member contains the real part of cdividend.

STRING Members

A gd_entry_t describing a STRING entry provides no additional data.

WINDOW Members

A gd_entry_t describing a WINDOW entry, will also provide:

typedef struct {
  ...
  const char    *in_fields[2];  /* input field codes */
  gd_windop_t   windop;         /* comparison operator */
  gd_triplet_t  threshold;      /* the value compared against */
  ...
} gd_entry_t;

The in_fields member contains the field codes of the input field (element 0) and the check field (element 1).

The windop member equals one of the following symbols, indicating the particular comparison performed on the check field:

GD_WINDOP_EQ: data are extracted when the check field equals threshold;
GD_WINDOP_GE: data are extracted when the check field is greater than or equal to threshold;
GD_WINDOP_GT: data are extracted when the check field is strictly greater than threshold;
GD_WINDOP_LE: data are extracted when the check field is less than or equal to threshold;
GD_WINDOP_LT: data are extracted when the check field is strictly less than threshold;
GD_WINDOP_NE: data are extracted when the check field is not equal to threshold;
GD_WINDOP_SET: data are extracted when at least one bit in threshold is also set in the check field;
GD_WINDOP_CLR: data are extracted when at least one bit in threshold is not set in the check field.

The threshold is the value against the check field is compared. The gd_triplet_t type is defined as:

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

The particular element of the union to use depends on the value of windop:

For GD_WINDOP_EQ and GD_WINDOP_NE, the signed integer element, threshold.i is set;
For GD_WINDOP_SET and GD_WINDOP_CLR, the unsigned integer element, threshold.u is set;
For all other values of windop, the floating point element, threshold.r is set.

NOTES

When using the C89 GetData API (by defining GD_C89_API before including getdata.h), the data types and names of several of the entry parameters are different. The following table lists the correspondences between members in the C99 and C89 APIs.

C99 API		C89 API
int	bitnum	int	u.bit.bitnum
int	numbits	int	u.bit.numbits
int	n_fields	int	u.lincom.n_fields
double complex	cm[3]	double	u.lincom.cm[3][2]
double	m[3]	double	u.lincom.m[3]
double complex	cb[3]	double	u.lincom.cb[3][2]
double	b[3]	double	u.lincom.b[3]
const char*	table	const char*	u.linterp.table
int	count_val	int	u.mplex.count_val
int	period	int	u.mplex.period
gd_shift_t	shift	gd_shift_t	u.phase.shift
int	poly_ord	int	u.polynom.poly_ord
double complex	ca[3]	double	u.polynom.ca[3][2]
double	a[3]	double	u.polynom.a[3]
unsigned int	spf	unsigned int	u.raw.spf
gd_type_t	data_type	gd_type_t	u.raw.data_type
double complex	cdividend	double	u.recip.cdividend[2]
double	dividend	double	u.recip.dividend
gd_type_t	const_type	gd_type_t	u.scalar.const_type
size_t	array_len	size_t	u.scalar.array_len
gd_windop_t	windop	gd_windop_t	u.window.windop
gd_triplet_t	threshold	gd_triplet_t	u.window.threshold

In the case of complex valued data in the C89 API, the first element of the two-element array is the real part of the complex number, and the second element is the imaginary part.

SYNOPSIS

DESCRIPTION

RETURN VALUE

THE ENTRY TYPE

Scalar Parameter Members

BIT and SBIT Members

CARRAY Members

CONST Members

INDEX Members

LINCOM Members

LINTERP Members

MPLEX Members

MULTIPLY and DIVIDE Members

PHASE Members

POLYNOM Members

RAW Members

RECIP Members

STRING Members

WINDOW Members

NOTES

SEE ALSO

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