CU Amiga Super CD-ROM 17

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Assembly Source File | 1994-02-14 | 11.3 KB | 257 lines

* TTL FAST FLOATING POINT ASCII TO FLOAT (FFPAFP) ************************************ * (C) COPYRIGHT 1980 MOTORLA INC. * ************************************ ********************************************************** * FFPAFP * * ASCII TO FLOAT * * * * INPUT: A0 - POINTER TO ASCII STRING OF FORMAT * * DESCRIBED BELOW * * * * OUTPUT: D7 - FAST FLOATING POINT EQUIVALENT * * A0 - POINTS TO THE CHARACTER WHICH * * TERMINATED THE SCAN * * * * CONDITION CODES: * * N - SET IF RESULT IS NEGATIVE * * Z - SET IF RESULT IS ZERO * * V - SET IF RESULT OVERFLOWED * * C - SET IF INVALID FORMAT DETECTED * * X - UNDEFINED * * * * REGISTERS D3 THRU D6 ARE CHANGED * * * * CODE SIZE: 246 BYTES STACK WORK: 8 BYTES * * * * INPUT FORMAT: * * * * {SIGN}{DIGITS}{'.'}{DIGITS}{'E'}{SIGN}{DIGITS} * * <*********MANTISSA********><*****EXPONENT****> * * * * SYNTAX RULES * * BOTH SIGNS ARE OPTIONAL AND ARE '+' OR '-'. * * THE MANTISSA MUST BE PRESENT. * * THE EXPONENT NEED NOT BE PRESENT. * * THE MANTISSA MAY LEAD WITH A DECIMAL POINT. * * THE MANTISSA NEED NOT HAVE A DECIMAL POINT. * * * * EXAMPLES: ALL OF THESE VALUES REPRESENT THE * * NUMBER ONE-HUNDRED-TWENTY. * * * * 120 .120E3 * * 120. +.120E+03 * * +120. 0.000120E6 * * 0000120.00 1200000E-4 * * 1200000.00E-0004 * * * * FLOATING POINT RANGE: * * * * FAST FLOATING POINT SUPPORTS THE VALUE ZERO * * AND NON-ZERO VALUES WITHIN THE FOLLOWING * * BOUNDS - * * * * 18 20 * * 9.22337177 X 10 > +NUMBER > 5.42101070 X 10 * * * * 18 -20 * * -9.22337177 X 10 > -NUMBER > -2.71050535 X 10 * * * * PRECISION: * * * * THIS CONVERSION RESULTS IN A 24 BIT PRECISION * * WITH GUARANTEED ERROR LESS THAN OR EQUAL TO * * ONE-HALF LEAST SIGNIFICANT BIT. * * * * * * NOTES: * * 1) THIS ROUTINE CALLS THE DUAL-BINARY TO FLOAT* * ROUTINE AND CAN BE USED AS AN ILLUSTRATION * * OF HOW TO 'FRONT-END' THAT ROUTINE WITH * * A CUSTOMIZED SCANNER. * * 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. * * 4) IF THE 'C' BIT IN THE CCR INDICATES AN * * INVALID PATTERN DETECTED, THEN A0 WILL * * POINT TO THE INVALID CHARACTER. * * * * LOGIC SUMMARY: * * * * A) PROCESS LEADING SIGN * * B) PROCESS PRE-DECIMALPOINT DIGITS AND * * INCREMENT 10 POWER BIAS FOR EACH * * DIGIT BYPASSED DUE TO 32 BIT OVERFLOW * * C) PROCESS POST-DECIMALPOINT DIGITS * * DECREMENTING THE 10 POWER BIAS FOR EACH * * D) PROCESS THE EXPONENT * * E) ADD THE 10 POWER BIAS TO THE EXPONENT * * F) CALL 'FFPDBF' ROUTINE TO FINISH CONVERSION * * * * TIMES: (8 MHZ NO WAIT STATES) * * 374 MICROSECONDS CONVERTING THE STRING * * * * * ********************************************************** PAGE *FFPAFP IDNT 1,1 FFP ASCII TO FLOAT * OPT PCS XDEF FFPAFP ENTRY POINT XREF FFPDBF FFPAFP MOVEQ #0,D7 CLEAR MANTISSA BUILD MOVEQ #0,D6 CLEAR SIGN+BASE10 BUILD * CHECK FOR LEADING SIGN BSR FPANXT OBTAIN NEXT CHARACTER BEQ.S FPANMB BRANCH DIGIT FOUND BCS.S FPANOS BRANCH NO SIGN ENCOUNTERED * LEADING SIGN ENCOUNTERED CMP.B #'-',D5 COMPARE FOR MINUS SEQ.B D6 SET ONES IF SO SWAP.W D6 SIGN TO HIGH WORD IN D6 * TEST FOR DIGIT OR PERIOD BSR FPANXT OBTAIN NEXT CHARACTER BEQ.S FPANMB BRANCH DIGIT TO BUILD MANTISSA FPANOS CMP.B #'.',D5 ? LEADING DECIMALPOINT BNE.S FPABAD BRANCH INVALID PATTERN IF NOT * INSURE AT LEAST ONE DIGIT BSR FPANXT OBTAIN NEXT CHARACTER BEQ.S FPADOF BRANCH IF FRACTION DIGIT * INVALID PATTERN DETECTED FPABAD SUBQ.L #1,A0 POINT TO INVALID CHARACTER * ORI #$01,CCR SET CARRY BIT ON DC.L $003C0001 ****ASSEMBLER ERROR**** RTS RETURN * PRE-DECIMALPOINT MANTISSA BUILD FPANXD BSR FPANXT NEXT CHARACTER BNE.S FPANOD BRANCH NOT A DIGIT FPANMB BSR.S FPAX10 MULTIPLY TIMES TEN BCC.S FPANXD LOOP FOR MORE DIGITS * PRE-DECIMALPOINT MANTISSA OVERFLOW, COUNT TILL END OR DECIMAL REACHED FPAMOV ADDQ.W #1,D6 INCREMENT TEN POWER BY ONE BSR.S FPANXT OBTAIN NEXT PATTERN BEQ.S FPAMOV LOOP UNTIL NON-DIGIT CMP.B #'.',D5 ? DECIMAL POINT REACHED BNE.S FPATSE NO, NO CHECK FOR EXPONENT * FLUSH REMAINING FRACTIONAL DIGITS FPASRD BSR.S FPANXT NEXT CHARACTER BEQ.S FPASRD IGNORE IT IF STILL DIGIT FPATSE CMP.B #'E',D5 ? EXPONENT HERE BNE.S FPACNV NO, FINISHED - GO CONVERT * NOW PROCESS THE EXPONENT BSR.S FPANXT OBTAIN FIRST DIGIT BEQ.S FPANTE BRANCH GOT IT BCS.S FPABAD BRANCH INVALID FORMAT, NO SIGN OR DIGITS ROL.L #8,D6 HIGH BYTE OF D6 INTO LOW CMP.B #'-',D5 ? MINUS SIGN SEQ.B D6 SET ONES OR ZERO ROR.L #8,D6 D6 HIGH BYTE IS EXPONENTS SIGN BSR.S FPANXT NOW TO FIRST DIGIT BNE.S FPABAD BRANCH INVALID - DIGIT EXPECTED * PROCESS EXPONENT'S DIGITS FPANTE MOVE.W D5,D4 COPY DIGIT JUST LOADED FPANXE BSR.S FPANXT EXAMINE NEXT CHARACTER BNE.S FPAFNE BRANCH END OF EXPONENT MULU.W #10,D4 PREVIOUS VALUE TIMES TEN CMP.W #2000,D4 ? TOO LARGE BHI.S FPABAD BRANCH EXPONENT WAY OF BASE ADD.W D5,D4 ADD LATEST DIGIT BRA.S FPANXE LOOP FOR NEXT CHARACTER * ADJUST FOR SIGN AND ADD TO ORIGINAL INDEX FPAFNE TST.L D6 ? WAS EXPONENT NEGATIVE BPL.S FPAADP BRANCH IF SO NEG.W D4 CONVERT TO NEGATIVE VALUE FPAADP ADD.W D4,D6 FINAL RESULT FPACNV SUBQ.L #1,A0 POINT TO TERMINATOR JMP FFPDBF NOW CONVERT TO FLOAT * PRE-DECIMALPOINT NON-DIGIT ENCOUNTERED FPANOD CMP.B #'.',D5 ? DECIMAL POINT HERE BNE.S FPATSE NOPE, TRY FOR THE 'E' * POST-DECIMALPOINT PROCESSING FPADPN BSR.S FPANXT OBTAIN NEXT CHARACTER BNE.S FPATSE NOT A DIGIT, TEST FOR E' FPADOF BSR.S FPAX10 TIMES TEN PREVIOUS VALUE BCS.S FPASRD FLUSH IF OVERFLOW NOW SUBQ.W #1,D6 ADJUST 10 POWER BIAS BRA.S FPADPN AND TO NEXT CHARACTER * * * * FPAX10 SUBROUTINE - PROCESS NEXT DIGIT * * OUTPUT: C=0 NO OVERFLOW, C=1 OVERFLOW (D7 UNALTERED) * * FPAX10 MOVE.L D7,D3 COPY VALUE LSL.L #1,D3 TIMES TWO BCS.S FPAXRT RETURN IF OVERFLOW LSL.L #1,D3 TIMES FOUR BCS.S FPAXRT RETURN IF OVERFLOW LSL.L #1,D3 TIMES EIGHT BCS.S FPAXRT RETURN IF OVERFLOW ADD.L D7,D3 ADD ONE TO MAKE X 9 BCS.S FPAXRT RETURN IF OVERFLOW ADD.L D7,D3 ADD ONE TO MAKE X 10 BCS.S FPAXRT RETURN IF OVERFLOW ADD.L D5,D3 ADD NEW UNITS DIGIT BCS.S FPAXRT RETURN IF OVERFLOW MOVE.L D3,D7 UPDATE RESULT FPAXRT RTS RETURN * * FPANXT SUBROUTINE - RETURN NEXT INPUT PATTERN * * INPUT: A0 * * OUTPUT: A0 INCREMENTED BY ONE * IF Z=1 THEN DIGIT ENCOUNTERED AND D5.L SET TO BINARY VALUE * IF Z=0 THEN D6.B SET TO CHARACTER ENCOUNTERED * AND C=0 IF PLUS OR MINUS SIGN * C=1 IF NOT PLUS OR MINUS SIGN * FPANXT MOVEQ #0,D5 ZERO RETURN REGISTER MOVE.B (A0)+,D5 LOAD CHARACTER CMP.B #'+',D5 ? PLUS SIGN BEQ.S FPASGN BRANCH IF SIGN CMP.B #'-',D5 ? MINUS SIGN BEQ.S FPASGN BRANCH IF SIGN CMP.B #'0',D5 ? LOWER THAN A DIGIT BCS.S FPAOTR BRANCH IF NON-SIGNDIGIT CMP.B #'9',D5 ? HIGHER THAN A DIGIT BHI.S FPAOTR BRANCH IF NON-SIGNDIGIT * IT IS DIGIT AND.B #$0F,D5 TO BINARY * MOVE.W #$0004,CCR SET Z=1 AND C=0 DC.L $44FC0004 ***ASSEMBLER ERROR*** RTS RETURN * IT IS SIGN FPASGN EQU * * MOVE.W #$0000,CCR SET Z=0 AND C=0 DC.L $44FC0000 ***ASSEMBLER ERROR*** RTS RETURN * IT IS NEITHER SIGN NOR DIGIT FPAOTR EQU * * MOVE.W #$0001,CCR SET Z=0 AND C=1 DC.L $44FC0001 ***ASSEMBLER ERROR*** RTS RETURN END