Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1459

FPTAN—Partial Tangent
Opcode
D9 F2
Description
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
obtained when computing the partial tangent of various classes of numbers, assuming
that underflow does not occur.
ST(0) SRC

 F
 0
 0
+F
+ 
NaN
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
integer multiple of 2 or by using the FPREM instruction with a divisor of 2.
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 reciprocal of the tangent) can be computed by executing a
FDIVR instruction after the FPTAN instruction.
Operation
IF ST(0)  2
THEN
C2  0;
ST(0)  tan(ST(0));
TOP  TOP  1;
ST(0)  1.0;
ELSE (*source operand is out-of-range *)
C2  1;
FI;
Volume 4: Base IA-32 Instruction Reference
Instruction
FPTAN
ST(0) DEST
*
 F to +F
 0
+0
 F to +F
*
NaN
can be reduced to the range of the instruction by subtracting an appropriate
63
Clocks Description
17-173 Replace ST(0) with its tangent and push 1 onto
the FPU stack.
63
. The following table shows the unmasked results
63
4:157