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Unformatted text preview: divided by the source operand in register ST(0), stores the result in ST(1), and pops the FPU register stack. The result in register ST(0) has the same sign as the source operand ST(1) and a magnitude less than +. The FPATAN instruction returns the angle between the X axis and the line from the origin to the point (X,Y), where Y (the ordinate) is ST(1) and X (the abscissa) is ST(0). The angle depends on the sign of X and Y independently, not just on the sign of the ratio Y/X. This is because a point (X,Y) is in the second quadrant, resulting in an angle between /2 and , while a point (X,Y) is in the fourth quadrant, resulting in an angle between 0 and /2. A point (X,Y) is in the third quadrant, giving an angle between /2 and . The following table shows the results obtained when computing the arctangent of various classes of numbers, assuming that underflow does not occur. 3354 Vol. 2 INSTRUCTION SET REFERENCE, AM Table 335. FPATAN Results
ST(0)   ST(1) F 0 +0 +F + NaN 3/4*   + + +3/4* NaN F /2  to /2  + + to +/2 +/2 NaN 0 /2 /2 * +* +/2 +/2 NaN +0 /2 /2 0* +0* +/2 +/2 NaN +F /2 /2 to  0 0 +0 +/2 to +0 +/2 NaN + /4* 0 0 +0 +0 +/4* NaN NaN NaN NaN NaN NaN NaN NaN NaN NOTES: F Means finite floatingpoint value. * Table 810 in the Intel 64 and IA32 Architectures Software Developer's Manual, Volume 1, specifies that the ratios 0/0 and / generate the floatingpoint invalid arithmeticoperation exception and, if this exception is masked, the floatingpoint QNaN indefinite value is returned. With the FPATAN instruction, the 0/0 or / value is actually not calculated using division. Instead, the arctangent of the two variables is derived from a standard mathematical formulation that is generalized to allow complex numbers as arguments. In this complex variable formulation, arctangent(0,0) etc. has well defined values. These values are needed to develop a library to compute transcendental functions with complex arguments, based on the FPU functions that only allow floatingpoint values as arguments. There is no restriction on the range of source operands that FPATAN can accept. This instruction's operation is the same in non64bit modes and 64bit mode. IA32 Architecture Compatibility
The source operands for this instruction are restricted for the 80287 math coprocessor to the following range: 0 ST(1) < ST(0) < + Operation
ST(1) arctan(ST(1) / ST(0)); PopRegisterStack; Vol. 2 3355 INSTRUCTION SET REFERENCE, AM FPU Flags Affected
C1 C0, C2, C3 Set to 0 if stack underflow occurred. Set if result was rounded up; cleared otherwise. Undefined. FloatingPoint Exceptions
#IS #IA #D #U #P Stack underflow occurred. Source operand is an SNaN value or unsupported format. Source operand is a denormal value. Result is too small for destination format. Value cannot be represented exactly in destination format. Protected Mode Exceptions
#NM #MF CR0.EM[bit 2] or CR0.TS[bit 3] = 1. If there is a pending x87 FPU exception. Real...
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This note was uploaded on 10/01/2013 for the course CPE 103 taught by Professor Watlins during the Winter '11 term at Mississippi State.
 Winter '11
 Watlins

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