Intel 80287, 80286 manual Fptan, STO 1r

PROGRAMMING NUMERIC APPLICATIONS

Table 2-8. FXAM Condition Code Settings

		Condition Code
				Interpretation
C3	C2	C1	CO
0	0	0	0	+	Unnormal
0	0	0	1	+	NaN
0	0	1	0	-	Unnormal
0	0	1	1	-	NaN
0	1	0	0	+	Normal
0	1	0	1	+00
0	1	1	0	-	Normal
0	1	1	1	-	00
1	0	0	0	+0
1	0	0	1	Empty
1	0	1	0	-0
1	0	1	1	Empty
1	1	0	0	+	Denormal
1	1	0	1	Empty
1	1	1	0	-·Denormal
1	1	1	1	Empty

Transcendental Instructions

The instructions in this group (table 2-9) perform the time-consuming core calculations for all common trigonometric, inverse trigonometric, hyperbolic, inverse hyperbolic, logarithmic, and exponential functions. Prologue and epilogue software may be used to reduce arguments to the range accepted by the instructions and to adjust the result to correspond to the original arguments if necessary. The transcendentals operate on the top one or two stack elements, and they return their results to the stack, also.

NOTE

The transcendental instructions assume that their operands are valid and in-range.The instruction descriptions in this section provide the allowed operand range of each instruction.

All operands to a transcendental must be normalized; denormals, unnormals, infinities, and NaNs are considered invalid. (Zero operands are accepted by some functions and are considered out-of-range by others). If a transcendental operand is invalid or out-of-range, the instruction will produce an undefined result without signalling an exception. It is the programmer's responsibility to ensure that operands are valid and in-range before executing a transcendental. For periodic functions, FPREM may be used to bring a valid operand into range.

FPTAN

o ::; ST(O) ::; 1r 14

FPTAN (partial tangent) computes the function Y IX = TAN (0). 0 is taken from the top stack element; it must lie in the range 0 ::; 0 ::; 7r14. The result of the operation is a ratio; Y replaces 0 in the stack and X is pushed, becoming the new stack top.

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