* TTL FAST FLOATING POINT DUAL-BINARY FLOAT (FFPDBF) ************************************ * (C) COPYRIGHT 1980 MOTOROLA INC. * ************************************ ********************************************************** * * * FAST FLOATING POINT DUAL-BINARY TO FLOAT * * * * INPUT: D6 BIT #16 - REPRESENTS SIGN (0=POSITIVE) * * (1=NEGATIVE) * * D6.W - REPRESENTS BASE TEN EXPONENT * * CONSIDERING D7 A BINARY INTEGER * * D7 - BINARY INTEGER MANTISSA * * * * OUTPUT: D7 - FAST FLOATING POINT EQUIVALENT * * * * CONDITION CODES: * * N - SET IF RESULT IS NEGATIVE * * Z - SET IF RESULT IS ZERO * * V - SET IF RESULT OVERFLOWED * * C - CLEARED * * X - UNDEFINED * * * * REGISTERS D3 THRU D6 DESTROYED * * * * CODE SIZE: 164 BYTES STACK WORK AREA: 4 BYTES * * * * * * PRECISION: * * * * THIS CONVERSION RESULTS IN A 24 BIT PRECISION * * WITH GUARANTEED ERROR LESS THAN OR EQUAL TO * * ONE-HALF LEAST SIGNIFICANT BIT. * * * * * * NOTES: * * 1) THE INPUT FORMATS HAVE BEEN DESIGNED FOR * * EASE OF PARSING TEXT FOR CONVERSION TO * * FLOATING POINT. SEE FFPASF FOR COMMENTS * * DESCRIBING THE METHOD FOR SETUP TO THIS * * ROUTINE. * * 2) UNDERFLOWS RETURN A ZERO WITHOUT ANY * * INDICATORS SET. * * 3) OVERFLOWS WILL RETURN THE MAXIMUM VALUE * * POSSIBLE WITH PROPER SIGN AND THE 'V' BIT * * SET IN THE CCR REGISTER. * * * ********************************************************** PAGE *FFPDBF IDNT 1,1 FFP DUAL-BINARY TO FLOAT * OPT PCS XDEF FFPDBF ENTRY POINT XREF FFP10TBL POWER OF TEN TABLE * NORMALIZE THE INPUT BINARY MANTISSA FFPDBF MOVEQ #32,D5 SETUP BASE 2 EXPONENT MAX TST.L D7 ? TEST FOR ZERO BEQ FPDRTN RETURN, NO CONVERSION NEEDED BMI.S FPDINM BRANCH INPUT ALREADY NORMALIZED MOVEQ #31,D5 PREPARE FOR NORMALIZE LOOP FPDNMI ADD.L D7,D7 SHIFT UP BY ONE DBMI D5,FPDNMI DECREMENT AND LOOP IF NOT YET * INSURE INPUT 10 POWER INDEX NOT WAY OFF BASE FPDINM CMP.W #18,D6 ? WAY TOO LARGE BGT.S FPDOVF BRANCH OVERFLOW CMP.W #-28,D6 ? WAY TOO SMALL BLT.S FPDRT0 RETURN ZERO IF UNDERFLOW MOVE.W D6,D4 COPY 10 POWER INDEX NEG.W D4 INVERT TO GO PROPER DIRECTION MULS.W #6,D4 TIMES FOUR FOR INDEX MOVE.L A0,-(SP) SAVE WORK ADDRESS REGISTER LEA FFP10TBL,A0 LOAD TABLE ADDRESS ADD.W 0(A0,D4.W),D5 ADD EXPONENTS FOR MULTIPLY MOVE.W D5,D6 SAVE RESULT EXPONENT IN D6.W * NOW PERFORM 32 BIT MULTIPLY OF INPUT WITH POWER OF TEN TABLE MOVE.L 2(A0,D4.W),D3 LOAD TABLE MANTISSA VALUE MOVE.L (SP),A0 RESTORE WORK REGISTER MOVE.L D3,(SP) NOW SAVE TABLE MANTISSA ON STACK MOVE.W D7,D5 COPY INPUT VALUE MULU.W D3,D5 TABLELOW X INPUTLOW CLR.W D5 LOW END NO LONGER TAKES AFFECT SWAP.W D5 SAVE INTERMEDIATE SUM MOVEQ #0,D4 CREATE A ZERO FOR DOUBLE PRECISION SWAP.W D3 TO HIGH TABLE WORD MULU.W D7,D3 INPUTLOW X TABLEHIGH ADD.L D3,D5 ADD ANOTHER PARTIAL SUM ADDX.B D4,D4 CREATE CARRY IF ANY SWAP.W D7 NOW TO INPUT HIGH MOVE.W D7,D3 COPY TO WORK REGISTER MULU.W 2(SP),D3 TABLELOW X INPUTHIGH ADD.L D3,D5 ADD ANOTHER PARTIAL BCC.S FPDNOC BRANCH NO CARRY ADDQ.B #1,D4 ADD ANOTHER CARRY FPDNOC MOVE.W D4,D5 CONCAT HIGH WORK WITH LOW SWAP.W D5 AND CORRECT POSITIONS MULU.W (SP),D7 TABLEHIGH X INPUTHIGH LEA 4(SP),SP CLEAN UP STACK ADD.L D5,D7 FINAL PARTIAL PRODUCT BMI.S FPDNON BRANCH IF NO NEED TO NORMALIZE ADD.L D7,D7 NORMALIZE SUBQ.W #1,D6 ADJUST EXPONENT FPDNON ADD.L #$80,D7 ROUND RESULT TO 24 BITS BCC.S FPDROK BRANCH ROUND DID NOT OVERFLOW ROXR.L #1,D7 ADJUST BACK ADDQ.W #1,D6 AND INCREMENT EXPONENT FPDROK MOVEQ #9,D3 PREPARE TO FINALIZE EXPONENT TO 7 BITS MOVE.W D6,D4 SAVE SIGN OF EXPONENT ASL.W D3,D6 FORCE 7 BIT PRECISION BVS.S FPDXOV BRANCH EXPONENT OVERFLOW EORI.W #$8000,D6 EXPONENT BACK FROM 2'S-COMPLEMENT LSR.L D3,D6 PLACE INTO LOW BYTE WITH SIGN MOVE.B D6,D7 INSERT INTO RESULT BEQ.S FPDRT0 RETURN ZERO IF EXPONENT ZERO FPDRTN RTS RETURN * RETURN ZERO FOR UNDERFLOW FPDRT0 MOVEQ #0,D7 LOAD ZERO RTS RETURN * EXPONENT OVERFLOW/UNDERFLOW FPDXOV TST.W D4 TEST ORIGINAL SIGN BMI.S FPDRT0 BRANCH UNDERFLOW TO RETURN ZERO FPDOVF MOVEQ #-1,D7 CREATE ALL ONES SWAP.W D6 SIGN TO LOW BIT ROXR.B #1,D6 SIGN TO X BIT ROXR.B #1,D7 SIGN INTO HIGHEST POSSIBLE RESULT TST.B D7 CLEAR CARRY BIT * ORI #$02,CCR SET OVERFLOW ON DC.L $003C0002 ****ASSEMBLER ERROR**** RTS RETURN TO CALLER WITH OVERFLOW END