User's Manual

PROGRAMMING NUMERIC APPLICATIONS
The assembler does not, however, check the types of operands used in processor control instructions.
Coding
FRSTOR [BP] implies that the programmer has set up register BP to point to the stack location
where the processor's 94-byte state record has been previously saved.
The initial values for 80287 constants may
be coded in several different ways. Binary integer constants
may
be specified as bit strings, decimal integers, octal integers, or hexadecimal strings. Packed decimal
values are normally written
as decimal integers, although the assembler will accept and convert other
representations of integers. Real values may be written as ordinary decimal real numbers (decimal
point required),
as decimal numbers in scientific notation, or as hexadecimal strings. Using hexadeci-
mal strings
is primarily intended for defining special values such as infinities, NaNs, and nonnormal-
ized numbers. Most programmers
will find that ordinary decimal and scientific decimal provide the
simplest way
to initialize 80287 constants. Figure 2-3 compares several ways of setting the various
80287 data types
to the same initial value.
Note that preceding 80287 variables and constants with the ASM286 EVEN directive ensures that the
operands
will be word-aligned in memory. This will produce the best system performance. All 80287
data types occupy integral numbers of words
so that no storage is "wasted" if blocks of variables are
defined together and preceded
by a single EVEN declarative.
RECORDS AND STRUCTURES
The ASM286 RECORD and STRUC (structure) declaratives can be very useful in NPX program-
ming. The record facility
can be used to define the bit fields of the control, status, and tag words.
Figure 2-4 shows one definition of the status word and how it might be used in a routine that polls the
80287 until it has completed an instruction.
Because STRUCtures allow different but related data types to
be grouped together, they often provide
a natural
way to represent "real world" data organizations. The fact that the structure template may
be "moved" about in memory adds to its flexibility. Figure 2-5 shows a simple structure that might be
used to represent data consisting of a series of test score samples. A structure could also
be used to
define the organization of the information stored and loaded by the FSTENV and FLDENV instructions.
THE FOLLOWING ALL ALLOCATE THI CONSTANT: -126
NOTE TWO'S COMPLETE STORAGE OF NEGATIVE BINARY INTEGERS,
EVEN
WORD_I NTEGER
SHORT_I NTEGER
DW
DD
111111111000010B
OFFFFFF82H
FORCE WORD ALIGNMENT
BIT STRING
HEX STRING MUST START
WITH DIGIT
LONG_INTEGER DQ -126 ORDINARY DECIMAL
SHORT_REAL DD -126,0 NOTE PRESENCE OF ' ,
LONG_REAL DD -1,26E2 "SCIENTIFIC"
PACKED_DECIMAL DT -126 ORDINARY DECIMAL INTEGER
IN THE FOLLOWING, SIGN AND EXPONENT IS 'COOS'
SIGNIFICAND IS '7EOO" ,00', 'R' INFORMS ASSEMBLER THAT
THE STRING REPRESENTS A REAL DATA TYPE,
DT OCOOS7EOOOOOOOOOOOOOOR HEX STRING
Figure 2-3. Sample 80287 Constants
2-41