Data Initialization File

The file, astb.df, and the Data Initialization File are external binary files defining the initialization of variables. astb.df is written by the Semantic Analyzer as it processes initializers for variables and is read by the ast transformer in order to write the necessary data initialization statements. The Data Initialization File is written by many phases of the compiler to effect data initialization statements for certain variables (format arrays, namelist descriptors, array constructors) created by the compiler; this file is also processed by the ast transformer.

The file , astb.df, is written by the semantic analyzer as it processes initialization statements; this includes DATA statements and initializers in type statements. The file consists of a sequence of records, where a group of three consecutive records represents a single DATA statement. The first record is a single word whose value (a 4-byte value) is the line number where the initialization occurred in the source file. The second record is a variable length record which is the Initializer Variable List (IVL) representing the variables, implied-do’s, etc. which are being initialized (see the chapter Semantic Analyzer). The third record is a variable length record which is the Initializer Constant Tree associated with the IVL (see the chapter Semantic Analyzer).

The Data Initialization File consists of one or more records. Each record consists of 2 fields, a short int (dtype) and a 32-bit INT (conval). Records are written to, and read from the file via the routines dinit_put and dinit_read in the module dinitutil.c. These routines are also responsible for opening and possibly buffering the file.

There are several types of record in the file, distinguished by the value of the first field (dtype):

dtype = DINIT_LOC

DINIT_LOC is a special value chosen so as to not conflict with any of the other possible values of this field. conval, the second field of the record, will be a symbol table pointer to a variable, array, pointer, or structure. This record indicates that a new symbol is being initialized. It results in the name of the variable being written. Ensuing records, up to the DINIT_END record, will initialize consecutive locations within this variable.

dtype = DINIT_FMT

The value of conval is the symbol table of the array which represents the format descriptor for the specifiers in a FORMAT statement. Ensuing records, up to the next DINIT_END, will initialize consecutive locations within this array.

dtype = DINIT_NML

The value of conval is the symbol table of the array which represents the namelist descriptor for the variables in a NAMELIST statement. Ensuing records, up to the next DINIT_END, will initialize consecutive locations within this array.

dtype = DINIT_END

This record marks the end of the initializers for the variable specified in the corresponding DINIT_LOC, DINIT_FMT, or DINIT_NML.

dtype = DT_DBLE

Indicates that 2 32-bit words are to be initialized with a 64-bit double precision floating point value. conval is a symbol table pointer to a double precision constant.

dtype = DT_CMPLX

Indicates that 2 32-bit words are to be initialized with two 32-bit floating point values. conval is a symbol table pointer to a complex constant.

dtype = DT_DCMPLX

Indicates that 2 64-bit words are to be initialized with two 64-bit double precision floating point values. conval is a symbol table pointer to a doublecomplex constant.

dtype = Fortran Hollerith or CHARACTER

dtype is actually DT_CHAR which indicates that a sequence of bytes is to be initialized to the characters in the Hollerith or CHARACTER string. conval is a symbol table pointer to the string constant. The length of the initialization is derived from the string’s DTYPE, not dtype.

dtype = other Fortran types

Includes the integer, logical, and single precision data types. Indicates that the value of the current initializer is conval.

dtype = DINIT_LABEL

Indicates that the next integer is to be initialized with the address of a variable. conval is the symbol table pointer for the variable. An initializer of this type does not actually appear in the DATA statement which is emitted. Instead, an assignment statement is added to the prologue of the subprogram and each applicable ENTRY. For example, a namelist descriptor requires the address of a variable.