Intel 80287, 80286 Fadd, Fsub, Fmulp, Fdiv Azimuth, Fidiv Npulses, Addition, Normal Subtraction

PROGRAMMING NUMERIC APPLICATIONS

Table 2-3. Basic Arithmetic Instructions and Operands

Instruction Form	Mnemonic	Operand Forms	ASM286 Example
	Form	destination, source
Classical stack	Fop	{ST(1),ST}	FADD
Register	Fop	ST(i),ST or ST,ST(i)	FSUB	ST,ST(3)
Register pop	FopP	ST(i),ST	FMULP	ST(2),ST
Real memory	Fop	{ ST,} short-realflong-real	FDIV	AZIMUTH
Integer memory	Flop	{ ST,} word-integerfshort-integer	FIDIV	N_PULSES

NOTES:

Braces ({ }) surround implicit operands; these are not coded, and are shown here for information only.

op = ADD destination +- destination + source SUB destination +- destination - source SUBR destination +- source - destination MUL destination +- destination·source DIV destination +- destination -7-source DIVR destination +- source -7-destination

Often the operand in the stack top is needed for one operation but then is of no further use in the computation. The register pop form can be used to pick up the stack top as the source operand, and then discard it by popping the stack. Coding operands of ST(1),ST with a register pop mnemonic is equivalent to a classical stack operation: the top is popped and the result is left at the new top.

The two memory forms increase the flexibility of the 80287's arithmetic instructions. They permit a real number or a binary integer in memory to be used directly as a source operand. This is a very useful facility in situations where operands are not used frequently enough to justify holding them in registers. Note that any memory addressing mode may be used to define these operands, so they may be elements in arrays, structures, or other data organizations, as well as simple scalars.

The six basic operations are discussed further in the next paragraphs, and descriptions of the remaining seven arithmetic operations follow.

ADDITION

FADD / /source/destination,source

FADDP / /destination/source

FIADD source

The addition instructions (add real, add real and pop, integer add) add the source and destination operands and return the sum to the destination. The operand at the stack top may be doubled by coding:

FADD ST,ST(O)

NORMAL SUBTRACTION

FSUB / /source/destination,source

FSUBP / /destination/source

FISUB source

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