Shareware Grab Bag/Shareware Grab Bag.iso/090/cmln1086.arc/ASSEMBLY.LTG

Text File | 1986-09-15 | 11KB | 320 lines

Assembly and High-Level Control Constructs by David Long

Listing 1

.xlist                          ;Listing off
;------------------------------------------
;Structured assembly language macro package
;
;For Microsoft/IBM macro assemblers
;
;Author: David Long
;Last edited: 07/08/86
;------------------------------------------
;
;-------------------
;Miscellaneous notes
;
;Only short jumps are generated for all constructs.  Separate stacks
;are used for each construct to facility adding constructs for abnormal
;termination (e.g., BREAK to exit a DO/WHILE/ENDWH loop).  Some notes
;on the assembler syntax: The & operator causes the macro parameter(s)
;immediately preceding/following it to be expanded (e.g., if FOO and BAR
;are parameters with values BAR and FOO respectively, FOO&BAR will expand
;as BARFOO).  The % operator causes evaluation of an expression (e.g.,
;if the label FOOBAR has the value 31, then calling a macro with the
;parameter %FOOBAR is the same as calling the macro with the parameter
;31 as a string, i.e., as the digits 3 and 1).
;-------------------
;
;-------------------
;Repeat/until macros
;Usage:
;_repeat        ;Beginning of loop
;   xxxxx       ;Body and test
;_until cc      ;Loop unless condition code cc holds
;-------------------
;
;_repeat generates the code for the start of a repeat statement.
;
_repeat macro
_push _rep,%_repcnt             ;;Save count on stack
_label _rep,%_repcnt            ;;Generate label for top of loop
_repcnt = _repcnt+01h
endm
;
;_until generates the code for the end of a repeat statement.
;
_until macro condition
_pop _rep                       ;;Get count for last _rep in _num
_mkijm condition,_rep,%_num     ;;Create jump with inverse condition code
endm
;
;---------------
;Do/while macros
;Usage:
;_do            ;Beginning of testè;   xxxxx       ;Loop test
;_while cc      ;Exit if condition code cc does not hold
;   xxxxx       ;Body
;_endwh         ;End of body - loop to start of test
;---------------
;
;_do generates the code for the beginning of a while statement.
;
_do macro
_push _while,%_whilecnt         ;;Save count on stack
_label _while,%_whilecnt        ;;Generate label for start of test
_whilecnt = _whilecnt+01h
endm
;
;_while generates the code for the middle part of a while statement.
;
_while macro condition
_pop _while                     ;;Get count for last _do in _num
_push _while,%_num              ;;Resave
_mkijm condition,_endwh,%_num   ;;Create jump with inverse condition code
endm
;
;_endwh generates the code for the end of a while statement.
;
_endwh macro
_pop _while                     ;;Get count for last _do in _num
_mkijm un,_while,%_num          ;;Create unconditional jump to test
_label _endwh,%_num             ;;Generate label for end of construct
endm
;
;-------------------
;If/else macros
;Usage:
;_if cc         ;Skip body if condition code cc does not hold
;   xxxxx       ;Body
;_endif         ;End of body
;or:
;_if cc         ;Skip to body of _else part if cc does not hold
;   xxxxx       ;Body of _if part
;_else          ;Skip to end of construct and mark start of _else part
;   xxxxx       ;Body of _else part
;_endif         ;End of construct
;-------------------
;
;_if generates the code for the beginning of an if statement.
;
_if macro condition
_push _else,%_elsecnt                   ;;Save count on stack
_mkijm condition,_else,%_elsecnt        ;;Create jump with inverse condition
_elsecnt = _elsecnt+01h
endm
;
;_else generates the code for the middle of an if statement.
;
_else macroè_pop _else                              ;;Get count for last _if in _num
_push _else,%_num                       ;;Resave
_mkijm un,_endif,%_num                  ;;Create unconditional jump to end
_label _else,%_num                      ;;Mark start of _else part
endm
;
;_endif generates the code for the end of an if statement.
;
_endif macro
_pop _else                              ;;Get count for last _if/_else
if1                                     ;;If pass 1
   _?def _else,%_num                    ;;   See if _elsexx is defined
   if _defined                          ;;   If so
      _label _endif,%_num               ;;      Label end of construct
   else                                 ;;   If not
      _label _else,%_num                ;;      Pretend the _else is here
   endif
endif
endm
;
;---------------------------------------------
;Utility macros for pushing numbers on a stack
;Usage:
;_push stacknm,num      ;Push num on stack named stacknm
;---------------------------------------------
;
;_push and _put push a number on the appropriate stack.
;
_push macro stacknm,num
;;Concatenate stacknm with '_ptr' to get the variable which has the top of
;;stack index (call the index n).  Call _put with the ASCII representation
;;of n together with stacknm and num.
_put stacknm,%&stacknm&_ptr,num
stacknm&_ptr = stacknm&_ptr+01h         ;;Increment stack pointer
endm
;
_put macro stacknm,pntr,num
;;Concatenate stacknm with '_st' and the ASCII representation of the
;;stack pointer to get a variable.  Assign num to that variable.
stacknm&_st&pntr = num
endm
;
;----------------------------------------------
;Utility macros for popping numbers off a stack
;Usage:
;_pop stacknm           ;Pop the stack named stacknm into the variable _num
;----------------------------------------------
;
;_pop and _fetch get a number off the appropriate stack.
;
_pop macro stacknm
ife stacknm&_ptr                                ;;If stack is empty
   %out Structured statement nesting error
else                                            ;;If stack is not empty
   stacknm&_ptr = stacknm&_ptr-01h              ;;   Decrement stack pointerè   ;;Concatenate stacknm with '_ptr' to get the variable which holds the
   ;;top of stack index (call the index n).  Call _fetch with the ASCII
   ;;representation of n, together with stacknm.
   _fetch stacknm,%&stacknm&_ptr
endif
endm
;
_fetch macro stacknm,pntr
;;Concatenate stacknm with '_st' and the ASCII represenation of the stack
;;pointer to get a variable.  Set _num to the value of that variable.
_num = stacknm&_st&pntr
endm
;
;------------------------------------------------------------------
;Utility macros for creating jumps with the opposite of a condition
;Usage:
;_mkijm condition,base,number   ;Create jump with inverse of condition
                                ;to the label formed by concatenating
                                ;base with number
;------------------------------------------------------------------
;
;_mkijm and _mkjmp create a jump instruction with the inverse of a condition.
;
_mkijm macro condition,base,number
_mkjmp %_inv_&condition,base&number     ;;Call _mkjmp with opcode and dest
endm
;
_mkjmp macro jmpopcode,dest
jmp short dest                          ;;Create jump (compute displacement)
org $-02h                               ;;Back up to jmp opcode
db jmpopcode                            ;;Install correct opcode
org $+01                                ;;Position back to end of jump
endm
;
;----------------------------
;Miscellaneous utility macros
;Usage:
;_label base,number             ;Concatenate base and number to form label
;_?def base,number              ;Form label from base and number.  Set
;                               ;_defined to zero if the label is undefined
;                               ;or set _defined nonzero if it is defined.
;----------------------------
;
;_label forms a label.
;
_label macro base,number
base&number label near
endm
;
;_?def checks to see if a label is defined.
;
_?def macro base,number
ifdef base&number
   _defined = 0ffh
elseè   _defined = 00h
endif
endm
;
;---------
;Variables
;---------
;
_inv_a      = 076h              ;Jump opcodes - jna = 076h
_inv_ae     = 072h              ;jnae = 072h
_inv_b      = 073h              ;jnb = 073h
_inv_be     = 077h              ;jnbe = 077h
_inv_c      = 073h              ;jnc = 073h
_inv_e      = 075h              ;jne = 075h
_inv_g      = 07eh              ;jng = 07eh
_inv_ge     = 07ch              ;   ...
_inv_l      = 07dh
_inv_le     = 07fh
_inv_na     = 077h
_inv_nae    = 073h
_inv_nb     = 072h
_inv_nbe    = 076h
_inv_nc     = 072h
_inv_ne     = 074h
_inv_ng     = 07fh
_inv_nge    = 07dh
_inv_nl     = 07ch
_inv_nle    = 07eh
_inv_no     = 070h
_inv_np     = 07ah
_inv_ns     = 078h
_inv_nz     = 074h
_inv_o      = 071h
_inv_p      = 07bh
_inv_pe     = 07bh
_inv_po     = 07ah
_inv_s      = 079h
_inv_z      = 075h
_inv_un     = 0ebh              ;Do not invert unconditional (jmp short)
_repcnt     = 00h               ;Number of last _rep
_elsecnt    = 00h               ;Number of last _if
_whilecnt   = 00h               ;Number of last _do
_rep_ptr    = 00h               ;Stack pointer for _rep stack
_else_ptr   = 00h               ;Stack pointer for _if stack
_while_ptr  = 00h               ;Stack pointer for _do stack
_num        = 00h               ;Number last popped off a stack
_defined    = 00h               ;Set by _?def (q.v.)
.xcref _num,_defined,_repcnt    ;Do not cross reference
.xcref _elsecnt,_whilecnt
.xcref _rep_ptr,_else_ptr
.xcref _while_ptr
.xcref _inv_a,_inv_ae,_inv_b,_inv_be
.xcref _inv_c,_inv_e,_inv_g,_inv_ge
.xcref _inv_l,_inv_le,_inv_na,_inv_nae
.xcref _inv_nb,_inv_nbe,_inv_nc,_inv_ne
.xcref _inv_ng,_inv_nge,_inv_nl,_inv_nle
.xcref _inv_no,_inv_np,_inv_ns,_inv_nz
.xcref _inv_o,_inv_p,_inv_pe,_inv_po
.xcref _inv_s,_inv_z,_inv_un
.list                           ;Listing back on


Listing 2

                ...
tab equ 09h                     ;ASCII horizontal tab character
                ...
include STRUCT.ASM              ;Include control structure macrosè                ...
;
;---------------------
;Procedure expand_tabs
;
;Expand tabs to spaces in string (assumes tabs every eight columns).
;
;Entry:
;  Pointer to string (00h terminated) in ds:si
;  Pointer to destination buffer in es:di
;  Direction flag clear
;Exit:
;  Ax, si, di altered
;---------------------
;
expand_tabs proc near
_do
   lodsb                        ;Get character in al
   test al,al
_while ne                       ;While not end of string
   cmp al,tab
   _if e                        ;If tab character
      mov al,' '                ;Will pad with spaces
      _repeat
         stosb                  ;Pad
         test di,000000111b
      _until z                  ;Repeat until eight character boundary
   _else                        ;If not tab
      stosb                     ;Save character
   _endif
_endwh
stosb                           ;Move 00h terminator
ret
expand_tabs endp
                ...