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shave some bytes #10

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1619c49
shave some bytes
peterferrie May 30, 2023
dc4ae49
one more
peterferrie May 30, 2023
08a21e0
one more
peterferrie May 30, 2023
a6e3c9d
one more
peterferrie May 30, 2023
f5a520f
restore call target
peterferrie May 30, 2023
acf1d66
a few more
peterferrie May 31, 2023
cc163e5
add missed label
peterferrie May 31, 2023
92effcb
one more
peterferrie May 31, 2023
74e7df7
one more
peterferrie May 31, 2023
9217f69
and one more
peterferrie May 31, 2023
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127 changes: 67 additions & 60 deletions sectorc.s
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Original file line number Diff line number Diff line change
Expand Up @@ -62,16 +62,20 @@ entry:
xor di,di ; codegen index, zero'd
;; [fall-through]

db 0x81 ; mask following call
;; [fall-through]
_is_int:
call tok_next2 ; consume "int" and <ident>
;; [fall-through]

;; main loop for parsing all decls
compile:
;; advance to either "int" or "void"
call tok_next

;; if "int" then skip a variable
cmp ax,TOK_INT
jne compile_function
call tok_next2 ; consume "int" and <ident>
jmp compile
je _is_int

compile_function: ; parse and compile a function decl
call tok_next ; consume "void"
Expand All @@ -98,26 +102,35 @@ execute:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; compile statements (optionally advancing tokens beforehand)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
_is_call:
xchg bx,ax
mov al,0xe8 ; emit "call" instruction
stosb

mov ax,[bx] ; load function offset from symbol-table
sub ax,di ; compute relative to this location: "dest - cur - 2"
dec ax
dec ax
stosw ; emit target
;; [fall-through] ; loop to compile next statement

compile_stmts_tok_next2:
call tok_next
compile_stmts_tok_next:
call tok_next
db 0x81 ; mask following call
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what does this 0x81 byte do?

;; [fall-through]
_not_while:
call compile_assign ; handle an assignment statement
;; [fall-through] ; loop to compile next statement

compile_stmts:
mov ax,bx
xchg bx,ax
cmp ax,TOK_BLK_END ; if we reach '}' then return
je return

test dh,dh ; if dh is 0, it's not a call
je _not_call
mov al,0xe8 ; emit "call" instruction
stosb

mov ax,[bx] ; load function offset from symbol-table
sub ax,di ; compute relative to this location: "dest - cur - 2"
sub ax,2
stosw ; emit target

jmp compile_stmts_tok_next2 ; loop to compile next statement
jne _is_call

_not_call:
cmp ax,TOK_ASM ; check for "asm"
Expand All @@ -128,29 +141,29 @@ _not_call:

_not_asm:
cmp ax,TOK_IF_BEGIN ; check for "if"
jne _not_if
call _control_flow_block ; compile control-flow block
jmp _patch_fwd ; patch up forward jump of if-stmt
je _is_if

_not_if:
cmp ax,TOK_WHILE_BEGIN ; check for "while"
jne _not_while
push di ; save loop start location
call _control_flow_block ; compile control-flow block
jmp _patch_back ; patch up backward and forward jumps of while-stmt

_not_while:
call compile_assign ; handle an assignment statement
jmp compile_stmts ; loop to compile next statement
;; [fall-through] ; patch up backward and forward jumps of while-stmt

_patch_back:
mov al,0xe9 ; emit "jmp" instruction (backwards)
stosb
pop ax ; restore loop start location
sub ax,di ; compute relative to this location: "dest - cur - 2"
sub ax,2
dec ax
dec ax
stosw ; emit target
;; [fall-through]
db 0x81 ; mask following call
_is_if:
call _control_flow_block ; compile control-flow block
;; [fall-through] ; patch up forward jump of if-stmt

_patch_fwd:
mov ax,di ; compute relative fwd jump to this location: "dest - src"
sub ax,si
Expand Down Expand Up @@ -180,13 +193,11 @@ return: ; this label gives us a way to do conditional re
compile_assign:
cmp ax,TOK_DEREF ; check for "*(int*)"
jne _not_deref_store
call tok_next ; consome "*(int*)"
call tok_next ; consume "*(int*)"
call save_var_and_compile_expr ; compile rhs first
;; [fall-through]

compile_store_deref:
mov bx,bp ; restore dest var token
mov ax,0x0489 ; code for "mov [si],ax"
;; [fall-through]

emit_common_ptr_op:
Expand All @@ -202,12 +213,11 @@ _not_deref_store:
;; [fall-through]

compile_store:
mov bx,bp ; restore dest var token
mov ax,0x0689 ; code for "mov [imm],ax"
mov ah,0x06 ; code for "mov [imm],ax"
jmp emit_var ; [tail-call]

save_var_and_compile_expr:
mov bp,bx ; save dest to bp
xchg bp,ax ; save dest to bp
call tok_next ; consume dest
;; [fall-through] ; fall-through will consume "=" before compiling expr

Expand All @@ -219,24 +229,19 @@ compile_expr_tok_next:
compile_expr:
call compile_unary ; compile left-hand side

push ds ; need to swap out 'ds' to scan the table with lodsw
push cs
pop ds

mov si,binary_oper_tbl - 2 ; load ptr to operator table (biased backwards)
push ds
push cs ; cannot use cs override!
pop ds ; because ';' here must be retained separately
mov cl,(binary_oper_tbl_e-binary_oper_tbl)/4
mov si,binary_oper_tbl ; load ptr to operator table (biased backwards)
_check_next:
lodsw ; discard 16-bit of machine-code
lodsw ; load 16-bit token value
cmp ax,bx ; matches token?
je _found
test ax,ax ; end of table?
jne _check_next

pop ds
ret ; all-done, not found
lodsw ; load 16-bit of machine-code
loopne _check_next ; lodsw does not affect flags
jne _not_found

_found:
lodsw ; load 16-bit of machine-code
push ax ; save it to the stack
mov al,0x50 ; code for "push ax"
stosb ; emit
Expand All @@ -258,9 +263,13 @@ emit_cmp_op:
;; [fall-through]

emit_op:
mov ax,bx
xchg bx,ax
stosw ; emit machine code for op

_not_found:
pop ds
mov bx,bp ; restore dest var token
mov ax,0x0489 ; code for "mov [si],ax"
ret

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
Expand Down Expand Up @@ -289,14 +298,15 @@ _not_paren:

_not_addr:
test dl,dl ; check for tok_is_num
je _not_int
mov ax,0x068b ; code for "mov ax,[imm]"
je _not_int ; mov does not affect flags
mov al,0xb8 ; code for "mov ax,imm"
stosb ; emit
jmp emit_tok ; [tail-call] to emit imm

db 0xf6 ; mask following stosw and add bx,bx
; [tail-call] to emit imm
;; [fall-through]
_not_int:
;; compile var
mov ax,0x068b ; code for "mov ax,[imm]"
;; [fall-through]

emit_var:
Expand All @@ -305,10 +315,10 @@ emit_var:
;; [fall-through]

emit_tok:
mov ax,bx
xchg bx,ax
stosw ; emit token value
jmp tok_next ; [tail-call]

db 0x81 ; mask following call [tail-call]
;; [fall-through]
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; get next token, setting the following:
;;; ax: token
Expand All @@ -331,21 +341,19 @@ tok_next:
setle dl ; tok_is_num = (al <= '9')

_nextch:
cmp al,32
jle _done ; if char is space then break

shl cx,8
mov ch,cl
mov cl,al ; shift this char into cx

imul bx,10
sub ax,48
add bx,ax ; atoi computation: bx = 10 * bx + (ax - '0')

call getch
jmp _nextch ; [loop]
cmp al,32
jg _nextch ; loop if char is not space

_done:
mov ax,cx
xchg cx,ax
cmp ax,0x2f2f ; check for single-line comment "//"
je _comment_double_slash
cmp ax,0x2f2a ; check for multi-line comment "/*"
Expand Down Expand Up @@ -381,16 +389,15 @@ getch:

getch_tryagain:
mov ax,0x0200
xor dx,dx
cwd
int 0x14 ; get a char from serial (bios function)

and ah,0x80 ; check for failure and clear ah as a side-effect
jne getch_tryagain ; failed, try again later

cmp al,59 ; check for ';'
jne getch_done ; if not ';' return it
mov [si],ax ; save the ';'
xor ax,ax ; return 0 instead, treated as whitespcae
xchg [si],ax ; save the ';', return 0 instead, treated as whitespcae

getch_done:
pop dx
Expand All @@ -414,7 +421,7 @@ binary_oper_tbl:
dw TOK_GT,0xc09f ; setg al
dw TOK_LE,0xc09e ; setle al
dw TOK_GE,0xc09d ; setge al
dw 0 ; [sentinel]
binary_oper_tbl_e:

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; boot signature
Expand Down