Examples of FORTH Assembler code: The following screens contain some handy words written in the FORTH 8086 Assembler. Using the assembler to define these words gains you speed, but costs you space: the assembler (about 6K) has to be there to assemble the words, and then you can't get rid of it. Therefore, the use of the examples is entirely up to you... ( Assembler examples, bit manipulation: << >> ~ ) CODE << ( n1 n2 -- n3 ;shift n1 left n2 times ) CX POP AX POP AX, CX SHL AX PUSH NEXT CODE >> ( n1 n2 -- n3 ;shift n1 right n2 places ) CX POP AX POP AX, CX SHR AX PUSH NEXT CODE ~ ( n -- ~n ;returns the one's complement of n ) AX POP AX NOT AX PUSH NEXT ( assembler examples: PICK, <CMOVE ) CODE PICK ( n -- m ;copy the nth stack item to the top, top=0 ) DI POP DI, 1 SHL ( index*2 ) BP PUSH BP, SP MOV AX, 2 [BP+DI] MOV ( get data ) BP POP AX PUSH NEXT CODE <CMOVE ( from to len -- ;backward CMOVE ) BX, SI MOV CX POP DI POP ( to) SI POP ( from) DI, CX ADD SI, CX ADD ( move from the ends ) DI DEC SI DEC DS PUSH ES POP ( all in one segment ) STD ( count down ) REP BYTE MOVS ( move it ) CLD SI, BX MOV NEXT ( assembler examples: ROLL ) CODE ROLL ( n -- ;roll the top n stack items, nth to top ) ( should check for 1<n<100 or so ) CX POP CX DEC CX, 1 SHL ( byte count ) BX, CX MOV ( index ) DI, SP MOV ( base ) AX, [BX+DI] MOV ( save nth element ) BX, SI MOV ( save IP ) DI, CX ADD SI, DI MOV SI, # 2 SUB CX, 1 SHR ( word count ) STD REP WORD MOVS CLD ( move top n-1 stack elements ) SI, BX MOV BX POP AX PUSH NEXT ( assembler examples: S->D ) CODE S->D ( n -- d; convert 16-bit to 32-bit signed number ) AX POP CWD AX PUSH DX PUSH NEXT ;S
