Intel 80286, 80287 manual Arithmetic Instructions

	PROGRAMMING NUMERIC APPLICATIONS
	Table 2-2. Arithmetic Instructions
	Addition
FADD	Add real
FADDP	Add real and pop
FIADD	Integer add
	Subtraction
FSUB	Subtract real
FSUBP	Subtract real and pop
FISUB	Integer subtract
FSUBR	Subtract real reversed
FSUBRP	Subtract real reversed and pop
FISUBR	Integer subtract reversed
	Multiplication
FMUL	Multiply real
FMULP	Multiply real and pop
FIMUL	Integer multiply
	Division
FDIV	Divide real
FDIVP	Divide real and pop
FIDIV	Integer divide
FDIVR	Divide real reversed
FDIVRP	Divide real reversed and pop
FIDIVR	Integer divide reversed
	Other Operations
FSQRT	Square root
FSCALE	Scale
FPREM	Partial remainder
FRNDINT	Round to integer
FXTRACT	Extract exponent and significand
FABS	Absolute value
FCHS	Change sign

Five basic instruction forms may be used across all six operations, as shown in table 2-3. The classicial stack form may be used to make the 80287 operate like a classical stack machine. No operands are coded in this form, only the instruction mnemonic. The NPX picks the source operand from the stack top and the destination from the next stack element. It then pops the stack, performs the operation, and returns the result to the new stack top, effectively replacing the operands by the result.

The register form is a generalization of the classical stack form; the programmer specifies the stack top as one operand and any register on the stack as the other operand. Coding the stack top as the destination provides a convenient way to access a constant, held elsewhere in the stack, from the stack top. The converse coding (ST is the source operand) allows, for example, adding the top into a register used as an accumulator.

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