C/C++ Users Group Library 1996 July

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ORG 0 NAM SMALL-C INTERPRETER OPT NOP,NOG * * LAST UPDATE 9-SEP-82 * JMP BEGIN START THE INTERPRETER * AN INDIRECT CALL TABLE NOP PUT ON A BOUNDARY OF 4 FCB 86 JMP fclose+1 FCB 86 JMP fopen+1 FCB 86 JMP getc+1 FCB 86 JMP getchar+1 FCB 86 JMP gets+1 FCB 86 JMP putc+1 FCB 86 JMP putchar+1 FCB 86 JMP puts+1 NOP JMP RTSC FCB 86 JMP isalpha+1 FCB 86 JMP isdigit+1 FCB 86 JMP isalnum+1 FCB 86 JMP islower+1 FCB 86 JMP isupper+1 FCB 86 JMP isspace+1 FCB 86 JMP toupper+1 FCB 86 JMP tolower+1 FCB 86 JMP strclr+1 FCB 86 JMP strlen+1 FCB 86 JMP strcpy+1 FCB 86 JMP strcat+1 FCB 86 JMP strcmp+1 RMB 4*4 ROOM FOR 4 MORE LIB FLEXPTRS NFILES EQU 4 MAX NO OF DISK FILES OPEN AT ONCE PC RMB 2 PSEUDO PROGRAM COUNTER R1A RMB 1 WORKING 16 BIT R1B RMB 1 --REGISTER DFLAG FCB NFILES-1 DIVIDE ROUTINE FLAG STEMP RMB 2 TEMP STORAGE FOR STACK POINTER X1TMP RMB 2 TEMP STORAGE FOR X REG X2TMP RMB 2 ... DITTO ... FCBPTR RMB 2 POINTER INTO FCB TABLE FCBTBL FDB FCB TABLE OF FCB POINTERS RMB NFILES*2 ROOM FOR THE REST *************************************************** BEGIN LDX #FCBTBL+2 POINT TO FCB ADDRESSES LDA A #NFILES-1 STA A DFLAG INIT COUNTER LDA A $AC2B GET TOP OF MEMORY LDA B $AC2C BLOOP SUB B #$40 SUBTR 320 (SIZE OF FCB) SBC A #1 STA A 0,X SAVE FCB ADDRESS INX STA B 0,X INX DEC DFLAG DONE ??? BNE BLOOP CLR 0,X MARK END OF TABLE CLR 1,X STA A STEMP TOP OF STACK AREA STA B STEMP+1 LDX STEMP TXS SET STACK POINTER LDX #FCBTBL POINT TO TABLE OF FCB ADDRESSES Init STX FCBPTR LDX 0,X GET FCB ADDRESS BEQ Initend QUIT IF END OF TABLE CLR 2,X MARK AS NOT IN USE LDX FCBPTR INX INX BRA Init Initend LDX #$800 BRA NEXT2 START THE INTERPRETATION ************************************************************** * * THE HEART OF THE INTERPRETER--- NEXT INSTRUCTION FETCHER. * BUMP2 LDX PC GET PROG COUNTER BUMP2A INX INCR BY 2 INX BRA NEXT1 FETCH NEXT INSTRUCTION NEXT LDX PC NEXT1 STA A R1A SAVE THE WORK STA B R1B --REGISTER NEXT2 LDA B 0,X GET THE PSEUDO-INSTRUCTION INX (B CONTAINS A TABLE OFFSET) STX PC SAVE NEW PC STA B JJJ+2 SAVE AS PAGE OFFSET LDA B R1B RESTORE JJJ LDX JTABLE POINT TO ROUTINE (SELF MODIFYING CODE) JMP 0,X GO EXECUTE THE PSEUDO-INSTR. ************************************************************** * THE JUMP TABLE * ************************************************************** ORG *+255/256*256 MUST START ON A PAGE BOUNDARY JTABLE FDB LD1IM #0 FDB LD1SOFF #1 FDB LD1 #2 FDB LDB1 #3 FDB LD1R #4 FDB LDB1R #5 FDB ST1 #6 FDB STB1 #7 FDB ST1SP #8 FDB STB1SP #9 FDB PUSHR1 #10 FDB EXG1 #11 FDB JMPL #12 FDB BRZL #13 FDB JSRL #14 FDB JSRSP #15 FDB RTSC #16 FDB MODSP #17 FDB DBL1 #18 FDB ADDS #19 FDB SUBFST #20 FDB MUL1 #21 FDB DIV1 #22 FDB MOD #23 FDB ORS #24 FDB XORS #25 FDB ANDS #26 FDB ASRS #27 FDB ASLS #28 FDB NEGR #29 FDB NOTR #30 FDB INCR #31 FDB DECR #32 FDB ZEQ #33 FDB ZNE #34 FDB ZLT #35 FDB ZLE #36 FDB ZGT #37 FDB ZGE #38 FDB ULT #39 FDB ULE #40 FDB UGT #41 FDB UGE #42 FDB ASMC #43 ************************************************************* *------------------------- * #0 LOAD REG WITH IMMED. VALUE LD1IM LDX PC LDA A 0,X HIGH BYTE LDA B 1,X LOW BYTE JMP BUMP2A *------------------------- * #1 LOAD STACK ADDRESS + OFFSET INTO REG LD1SOFF STS R1A SAVE STACK VALUE LDX PC LDA A 0,X GET OFFSET LDA B 1,X -- VALUE SEC ADC B R1B ADD OFFSET + 1 ADC A R1A JMP BUMP2A *------------------------- * #2 LOAD WORD @ ADDRESS LD1 LDX PC LDX 0,X GET ADDRESS LD1A LDA A 0,X GET WORD LDA B 1,X JMP BUMP2 *------------------------- * #3 LOAD BYTE @ ADDRESS LDB1 LDX PC LDX 0,X GET ADDRESS CLR A LDA B 0,X GET BYTE BPL LDB1A COM A SIGN EXTEND LDB1A JMP BUMP2 *------------------------- * #4 LOAD WORD INDIRECT (ADDR IN REG) LD1R LDX R1A GET ADDRESS LDA A 0,X GET WORD LDA B 1,X JMP NEXT *------------------------- * #5 LOAD BYTE INDIRECT (ADDR IN REG) LDB1R LDX R1A CLR A LDA B 0,X GET BYTE BPL LDB1RA COM A LDB1RA JMP NEXT *------------------------- * #6 STORE WORD @ ADDRESS ST1 LDX PC LDX 0,X GET ADDRESS STA A 0,X STORE WORD STA B 1,X JMP BUMP2 *------------------------- * #7 STORE BYTE @ ADDRESS STB1 LDX PC LDX 0,X GET ADDR STA B 0,X STORE BYTE JMP BUMP2 *------------------------- * #8 STORE WORD @ ADDRESS ON STACK ST1SP TSX STACK TO INDEX LDX 0,X GET ADDRESS STA A 0,X STORE WORD STA B 1,X INS INS POP STACK JMP NEXT *------------------------- * #9 STORE BYTE @ ADDRESS ON STACK STB1SP TSX LDX 0,X STA B 0,X STORE BYTE INS POP ... INS JMP NEXT *------------------------- * #10 PUSH WORD ON STACK PUSHR1 PSH B PSH A LDX PC JMP NEXT2 *------------------------- * #11 SWAP REG AND TOP OF STACK EXG1 TSX LDX 0,X GET VALUE ON STACK STX R1A SAVE INS INS PSH B PSH A REG ON STACK LDA A R1A NEW REG LDA B R1B LDX PC JMP NEXT2 *------------------------- * #12 JUMP TO LABEL JMPL LDX PC JMP1 LDX 0,X GET ADDRESS (NEW PC) JMP NEXT2 *------------------------- * #13 JUMP TO LABEL IF FALSE BRZL ORA A R1B SET FLAGS BEQ JMPL IF REG=0 -- JUMP JMP BUMP2 ELSE, PROCEED *------------------------- * #14 CALL TO LABEL JSRL LDX PC INX ADJUST RETURN INX -- ADDRESS DES STS *+5 *** SELF MODIFYING CODE *** DES STX $FFFF PUSH RETURN ADDRESS BRA JMPL *------------------------- * #15 CALL TO TOP OF STACK JSRSP TSX POINT TO STACK LDX 0,X GET ADDRESS (NEW PC) INS POP INS LDA B PC+1 GET RETURN ADDRESS PSH B LDA B PC PSH B SAVE RETURN ADDRESS JMP NEXT2 *------------------------- * #16 RETURN TO CALLER RTSC TSX LDX 0,X GET ADDRESS INS POP INS JMP NEXT1 *------------------------- * #17 MODIFY THE STACK POINTER MODSP LDX PC LDA A 0,X GET VALUE LDA B 1,X STS STEMP ADD B STEMP+1 ADD STACK POINTER ADC A STEMP STA A STEMP STA B STEMP+1 LDS STEMP NEW STACK POINTER LDA A R1A RESTORE REGISTER LDA B R1B JMP BUMP2A *--------------------------- * #18 DOUBLE THE PRIMARY REGISTER DBL1 ASL B ROL A JMP NEXT *--------------------------- * #19 ADD REG AND TOP OF STACK (THEN POP) ADDS TSX ADD B 1,X DO THE ADD ADC A 0,X JMP POPS POP & RETURN *--------------------------- * #20 SUBTRACT REG FROM TOP OF STACK SUBFST PUL A GET VALUE OFF STACK PUL B SUB B R1B SUBTRACT REGISTER SBC A R1A JMP NEXT *--------------------------- * #21 MULTIPLY TOP OF STACK BY REG (RESULT IN REG) MUL1 PSH B PSH A REG ON STACK LDA A #16 PSH A SET COUNTER CLR A CLR B TSX POINT TO DATA M2 ROR 3,X SHIFT MULTIPLIER ROR 4,X DEC 0,X DONE ? BMI M4 BCC M3 ADD B 2,X ADC A 1,X M3 ROR A ROR B SHIFT RESULT BRA M2 AND LOOP M4 INS CLEAN STACK INS INS PUL A GET RESULT PUL B JMP NEXT *----------------------------- * #22 DIVIDE THE TOP OF STACK BY REG --- RESULT IN REG. DIV1 BSR BDIV DO THE BASIC DIVIDE LDA A DFLAG GET SIGN FLAG AND A #1 MASK OFF BIT ZERO PUL A GET RESULT PUL B BEQ DIV1R DIV1N BSR NEGATE NEGATE THE VALUE IN A,B DIV1R JMP NEXT *----------------------------- * #23 DIVIDE TOP OF STACK BY REG --- REMAINDER IN REG MOD BSR BDIV INS CLEAN STACK INS PSH A TEMP SAVE LDA A DFLAG GET SIGN FLAG BPL MOD1 COM A MOD1 AND A #1 MASK OFF BIT 0 PUL A BNE DIV1N IF BIT 0 SET, NEGATE JMP NEXT ***************************************************** * BASIC 16 BIT DIVIDE ROUTINE * ENTER WITH: DIVIDEND ON STACK * DIVISOR IN A,B * EXIT WITH: QUOTIENT ON STACK * REMAINDER IN A,B * SIGN FLAG IN DFLAG * BDIV CLR DFLAG TST A CHECK DIVISOR SIGN BPL BDIV1 INC DFLAG ADJUST SIGN FLAG BSR NEGATE TAKE ABSOLUTE VALUE BDIV1 PSH B FORCE ON STACK PSH A LDA A #17 BIT COUNTER PSH A TSX POINT TO DATA LDA A 5,X CHECK SIGN BPL BDIV2 -- OF DIVIDEND COM DFLAG A