Intel 80286, 80287 manual Numeric Programming Examples, Conditional Branching for Fxam Contd

NUMERIC PROGRAMMING EXAMPLES

iCALCULATE OFFSET INTO JUMP TABLE

MOV	BH,O	i	CLEAR	UPPER HALF OF	BX,
MOV	Bl,AH	i	lOAD CONDITION CODE		INTO BL
AND	BL,OOOOOIIIB			i CLE~R ALL BITS EXCEPT C2-CO
AND	AH,01000000B			i CLEAR ALL BITS EXCEPT C3
SHR	AH,2		SHIFT	C3 TWO PLACES	RIGHT
SAL	BX,1		SHIFT	C2-CO 1 PLACE LEFT (MULTIPLY
			BY 2)
OR	Bl,AH		DROP	C3 BACK IN ADJACENT TO C2

(OOOXXXXO)

iJUMP TO THE ROUTINE 'ADDRESSED' BY CONDITION CODE

JMP FXAM_TBLIBXl

HERE ARE THE JUMP TARGETS, ONE TO HANDLE

iEACH POSSIBLE RESULT OF fXAM

PO LU NNOR M:

POS_NAN:

NELU NNOR M:

NELN AN:

PO LN 0 RM:

POLINFINITY:

NELH 0 RM:

NELINFINITY:

PO LZ E: R0:

EMPTY:

NELZERO:

PO LDE H0 RM:

HELDENORM:

Figure 4-2. Conditional Branching for FXAM (Cont'd.)

EXCEPTION HANDLING EXAMPLES

There are many approaches to writing exception handlers. One useful technique is to consider the exception handler procedure as consisting of "prologue," "body," and "epilogue" sections of code. (For compatibility with the 80287 emulators, this procedure should be invoked by interrupt pointer (vector) number 16.)

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