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3-312 Vol. 2A FCOS—Cosine
INSTRUCTION SET REFERENCE, A-M
FCOS—Cosine
Description
Computes the cosine of the source operand in register ST(0) and stores the result in
ST(0). The source operand must be given in radians and must be within the range −
2
63
to +2
63
. The following table shows the results obtained when taking the cosine of
various classes of numbers.
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 2π or by using the FPREM instruction with a divisor of
2π. See the section titled “Pi” in Chapter 8 of the Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 1, for a discussion of the proper value to use
for π in performing such reductions.
This instruction’s operation is the same in non-64-bit modes and 64-bit mode.
Operation
IF |ST(0)| < 2
63
THEN
C2 ← 0;
Opcode Instruction 64-Bit
Mode
Compat/
Leg Mode
Description
D9 FF FCOS Valid Valid Replace ST(0) with its cosine.
Table 3-28. FCOS Results
ST(0) SRC ST(0) DEST
−∞ *
−F −1 to +1
−0 +1
+0 +1
+F −1 to +1
+
∞ *
NaN NaN
NOTES:
F Means finite floating-point value.
* Indicates floating-point invalid-arithmetic-operand (#IA) exception.