3-229
INSTRUCTION SET REFERENCE
FPTANPartial Tangent
Description
This instruction computes the tangent of the source operand in register ST(0), stores the result
in ST(0), and pushes a 1.0 onto the FPU register stack. The source operand must be given in
radians and must be less than ±2
63
. The following table shows the unmasked results obtained
when computing the partial tangent of various classes of numbers, assuming that underflow does
not occur.
NOTES:
FMeans finite-real number.
*Indicates floating-point invalid-arithmetic-operand (#IA) exception.
If the source operand is outside the acceptable range, the C2 flag in the FPU status word is set,
and the value in register ST(0) remains unchanged. The instruction does not raise an exception
when the source operand is out of range. It is up to the program to check the C2 flag for out-of-
range conditions. Source values outside the range
?
2
63
to +2
63
can be reduced to the range of the
instruction by subtracting an appropriate integer multiple of 2
?
or by using the FPREM instruc-
tion with a divisor of 2
?
. Refer to Section 7.5.8., Pi in Chapter 7, Floating-Point Unit of the Intel
Architecture Software Developers Manual, Volume 1, for a discussion of the proper value to use
for
?
in performing such reductions.
The value 1.0 is pushed onto the register stack after the tangent has been computed to maintain
compatibility with the Intel 8087 and Intel287 math coprocessors. This operation also simplifies
the calculation of other trigonometric functions. For instance, the cotangent (which is the recip-
rocal of the tangent) can be computed by executing a FDIVR instruction after the FPTAN
instruction.
Opcode
Instruction
Clocks
Description
D9 F2
FPTAN
17-173
Replace ST(0) with its tangent and push 1
onto the FPU stack.
ST(0) SRC
ST(0) DEST
??
*
?
F
?
F to +F
?
0
?
0
+
0
+0
+F
?
F to +F
+
?
*
NaN
NaN
