image/svg+xml FCOS— Cosine Description Computes the approximate 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 2 π. However, even within the range -2 63 to +2 63 , inaccurate results can occur because the finite approximation of π used internally for argument reduction is not sufficient in all cases. Therefore, for accurate results it is safe to apply FCOS only to arguments reduced accurately in software, to a value smaller in absolute value than 3 π /8. See the sections titled “Approximation of Pi” and “Transcendental Instruction Accuracy” 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; ST(0) := FCOS(ST(0)); // approximation of cosine ELSE (* Source operand is out-of-range *) C2 := 1; FI; OpcodeInstruction64-Bit Mode Compat/ Leg Mode Description D9 FFFCOSValidValidReplace ST(0) with its approximate cosine. Table 3-23. FCOS Results ST(0) SRCST(0) DEST − ∞ * − F − 1 to + 1 − 0 + 1 + 0 + 1 + F − 1 to + 1 + ∞ * NaNNaN NOTES: FMeans finite floating-point value. * Indicates floating-point invalid-arithmetic-operand (#IA) exception. image/svg+xml FPU Flags Affected C1Set to 0 if stack underflow occurred. Set if result was rounded up; cleared otherwise. Undefined if C2 is 1. C2Set to 1 if outside range ( − 2 63 < source operand < + 2 63 ); otherwise, set to 0. C0, C3 Undefined. Floating-Point Exceptions #ISStack underflow occurred. #IASource operand is an SNaN value, ∞ , or unsupported format. #DSource is a denormal value. #PValue cannot be represented exactly in destination format. Protected Mode Exceptions #NMCR0.EM[bit 2] or CR0.TS[bit 3] = 1. #MF If there is a pending x87 FPU exception. #UD If the LOCK prefix is used. Real-Address Mode Exceptions Same exceptions as in protected mode. Virtual-8086 Mode Exceptions Same exceptions as in protected mode. Compatibility Mode Exceptions Same exceptions as in protected mode. 64-Bit Mode Exceptions Same exceptions as in protected mode. This UNOFFICIAL reference was generated from the official Intel® 64 and IA-32 Architectures Software Developer’s Manual by a dumb script. There is no guarantee that some parts aren't mangled or broken and is distributed WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE .