Intel 80286, 80287 manual Fcompp, Fxam

PROGRAMMING NUMERIC APPLICATIONS

NaNs and co (projective) cannot be compared and return C3 =CO= 1 as shown in the table.

FCOMP / /source

FCOMP (compare real and pop) operates like FCOM, and in addition pops the stack.

FCOMPP

FCOMPP (compare real and pop twice) operates like FCOM and additionally pops the stack twice, discarding both operands. The comparison is of the stack top to ST(1); no operands may be explicitly coded.

FICOM source

FICOM (integer compare) converts the source operand, which may reference a word or short binary integer variable, to temporary real and compares the stack top to it.

FICOMP source

FICOMP (integer compare and pop) operates identically to FICOM and additionally discards the value in ST by popping the stack.

FTST

FTST (test) tests the top stack element by comparing it to zero. The result is posted to the condition codes as shown in table 2-7.

FXAM

FXAM (examine) reports the content of the top stack element as positive/negative and NaN/unnor- mal/denormal/normal/zero, or empty. Table 2-8 lists and interprets all the condition code values that FXAM generates. Although four different encodings may be returned for an empty register, bits C3 and CO of the condition code are both 1 in all encodings. Bits C2 and Cl should be ignored when examining for empty.

Table 2-7. Condition Code Interpretation after FTST

	Condition Code
				Interpretation after FTST
C3	C2	C1	CO
0	0	X	0	ST> 0
0	0	X	1	ST< 0
1	0	X	0	ST = 0
1	1	X	1	ST is not comparable; (i.e., it is a NaN or projective infinity)
				2-11