Category : C++ Source Code
Archive   : VCCRT1.ZIP
Filename : SETSEG.ASM

page ,132
title setseg - Heap segment check/set routine
;***
;setseg.asm - Heap segment check/set routine
;
; Copyright (c) 1988-1992, Microsoft Corporation. All rights reserved.
;
;Purpose:
; Does a minimal heap segment consistency check and, optionally,
; fills all free nodes with a specified value.
;
;*******************************************************************************

.xlist
include version.inc
include cmacros.inc
include heap.inc
.list

externNP _headchk ; validate a heap descriptor header

sBegin code

assumes cs,code

page
;***
; _setseg - Heap segment check/set routine
;
;Purpose:
; Does a minimal heap segment consistency check and, optionally,
; fills all free nodes with a specified value.
;
;Entry:
; cx = fill value (_HEAPSET_NOFILL means don't fill)
; ds:bx = heap descriptor
;
;Exit:
; ax = return value as follows:
;
; _HEAPOK - completed okay
; _HEAPEMPTY - near heap not initialized
; _HEAPBADBEGIN - bogus header
; _HEAPBADNODE - malformed node somewhere
;
;Uses:
;
;Exceptions:
;
;*******************************************************************************

cProc _setseg,,<>

localW RoverCnt

cBegin

;
; --- Validate the header portion of the heap descriptor
;

call _headchk ; heap head check
cmp ax,_HEAPOK ; is it ok ?
jne done ; nope, all done

;
; --- Scan the heap
; Run through the heap looking for bogosity. Also, set the free
; blocks with the 'fill value' if appropriate.
;

; Setup for the heap scan
cld ; scan forward

mov [RoverCnt],0 ; clear rover flag

push ds ; es = heap descriptor segment
pop es

mov dx,[bx].segsize ; dx = size of segment
dec dx ; in case size == 0 (i.e., 64kb)

mov si,[bx].start ; si = pointer to first entry
jmp short check_block ; jump into the fray

next_block: ; validate the next block
add si,ax ; no, bump pointer to next block
jc bad_node ; overflow = bad node
cmp si,dx ; new address > size of segment ??
ja bad_node ; yup, bad node

check_block:
cmp [bx].rover,si ; current header == rover?
jne check_block2 ; nope, continue
inc [RoverCnt] ; yes, bump counter
check_block2: ; get the header from this block
lodsw ; ax = block header
cmp ax,_HEAP_END ; are we at the end ??
je heap_end ; yup, end of heap

test al,1 ; is it free ??
jz next_block ; no, onto next block

; block is free - see if we should fill it
dec ax ; ax = length of free block
cmp cx,_HEAPSET_NOFILL ; should we fill it ??
je next_block ; no, onto next block

; fill the free block
push ax ; save length for later
push cx ; save fill value
shr ax,1 ; ax = word count
xchg ax,cx ; cx = length, ax = fill char
mov ah,al ; ah = al = fill char
mov di,si ; es:di = address of free block
rep stosw ; fill 'er up
pop cx ; cx = fill value
pop ax ; ax = length

jmp short next_block ; onto the next block

;
; --- Bad heap node return
;

bad_node:
mov ax,_HEAPBADNODE ; bad heap node
jmp short done ; join common return

;
; --- End of Heap
; ax = _HEAP_END
; si = pointer to last entry + 2
;

heap_end:
.ERRE _HEAP_END EQ _HEAPOK ; Sleezy trick to save a "mov"...
;mov ax,_HEAPOK ; heap is ok

dec si
dec si ; si = addr _HEAP_END
cmp si,[bx].last ; did we find the "real" end ??
jne bad_node ; nope, return an error

cmp [RoverCnt],1 ; Did we find one and only one rover ??
jne bad_node ; nope, return an error

;fall thru ; good return

;
; --- Common return
; ax = return value
;

done:

cEnd

sEnd code

end