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+;       SCCSID = @(#)alloc.asm  1.1 85/04/09
+TITLE ALLOC.ASM - memory arena manager
+NAME Alloc
+;
+; Memory related system calls and low level routines for MSDOS 2.X.
+; I/O specs are defined in DISPATCH.
+;
+;   $ALLOC
+;   $SETBLOCK
+;   $DEALLOC
+;   $AllocOper
+;   arena_free_process
+;   arena_next
+;   check_signature
+;   Coalesce
+;
+;   Modification history:
+;
+;       Created: ARR 30 March 1983
+;
+
+.xlist
+;
+; get the appropriate segment definitions
+;
+include dosseg.asm
+
+CODE    SEGMENT BYTE PUBLIC  'CODE'
+        ASSUME  SS:DOSGROUP,CS:DOSGROUP
+
+.xcref
+INCLUDE DOSSYM.INC
+INCLUDE DEVSYM.INC
+.cref
+.list
+
+.lall
+
+SUBTTL memory allocation utility routines
+PAGE
+;
+; arena data
+;
+        i_need  arena_head,WORD         ; seg address of start of arena
+        i_need  CurrentPDB,WORD         ; current process data block addr
+        i_need  FirstArena,WORD         ; first free block found
+        i_need  BestArena,WORD          ; best free block found
+        i_need  LastArena,WORD          ; last free block found
+        i_need  AllocMethod,BYTE        ; how to alloc first(best)last
+        I_need  EXTERR_LOCUS,BYTE       ; Extended Error Locus
+
+;
+; arena_free_process
+; input:    BX - PID of process
+; output:   free all blocks allocated to that PID
+;
+        procedure   arena_free_process,NEAR
+        ASSUME  DS:NOTHING,ES:NOTHING
+        MOV     DI,arena_signature
+        MOV     AX,[arena_head]
+        CALL    Check_Signature         ; ES <- AX, check for valid block
+
+arena_free_process_loop:
+        retc
+        PUSH    ES
+        POP     DS
+        CMP     DS:[arena_owner],BX     ; is block owned by pid?
+        JNZ     arena_free_next         ; no, skip to next
+        MOV     DS:[arena_owner],DI     ; yes... free him
+
+arena_free_next:
+        CMP     BYTE PTR DS:[DI],arena_signature_end
+                                        ; end of road, Jack?
+        retz                            ; never come back no more
+        CALL    arena_next              ; next item in ES/AX carry set if trash
+        JMP     arena_free_process_loop
+
+EndProc arena_free_process
+
+;
+; arena_next
+; input:    DS - pointer to block head
+; output:   AX,ES - pointers to next head
+;           carry set if trashed arena
+;
+        procedure   arena_next,NEAR
+        ASSUME  DS:NOTHING,ES:NOTHING
+        MOV     AX,DS                   ; AX <- current block
+        ADD     AX,DS:[arena_size]      ; AX <- AX + current block length
+        INC     AX                      ; remember that header!
+;
+;       fall into check_signature and return
+;
+;       CALL    check_signature         ; ES <- AX, carry set if error
+;       RET
+EndProc arena_next
+
+;
+; check_signature
+; input:    AX - address of block header
+; output:   ES=AX, carry set if signature is bad
+;
+        procedure   check_signature,NEAR
+        ASSUME  DS:NOTHING,ES:NOTHING
+        MOV     ES,AX                   ; ES <- AX
+        CMP     BYTE PTR ES:[DI],arena_signature_normal
+                                        ; IF next signature = not_end THEN
+        retz                            ;   GOTO ok
+        CMP     BYTE PTR ES:[DI],arena_signature_end
+                                        ; IF next signature = end then
+        retz                            ;   GOTO ok
+        STC                             ; set error
+        return
+
+EndProc Check_signature
+
+;
+; Coalesce - combine free blocks ahead with current block
+; input:    DS - pointer to head of free block
+; output:   updated head of block, AX is next block
+;           carry set -> trashed arena
+;
+        procedure   Coalesce,NEAR
+        ASSUME  DS:NOTHING,ES:NOTHING
+        CMP     BYTE PTR DS:[DI],arena_signature_end
+                                        ; IF current signature = END THEN
+        retz                            ;   GOTO ok
+        CALL    arena_next              ; ES, AX <- next block, Carry set if error
+        retc                            ; IF no error THEN GOTO check
+
+coalesce_check:
+        CMP     ES:[arena_owner],DI
+        retnz                           ; IF next block isnt free THEN return
+        MOV     CX,ES:[arena_size]      ; CX <- next block size
+        INC     CX                      ; CX <- CX + 1 (for header size)
+        ADD     DS:[arena_size],CX      ; current size <- current size + CX
+        MOV     CL,ES:[DI]              ; move up signature
+        MOV     DS:[DI],CL
+        JMP     coalesce                ; try again
+EndProc Coalesce
+
+SUBTTL $Alloc - allocate space in memory
+PAGE
+;
+;   Assembler usage:
+;           MOV     BX,size
+;           MOV     AH,Alloc
+;           INT     21h
+;         AX:0 is pointer to allocated memory
+;         BX is max size if not enough memory
+;
+;   Description:
+;           Alloc returns  a  pointer  to  a  free  block of
+;       memory that has the requested  size  in  paragraphs.
+;
+;   Error return:
+;           AX = error_not_enough_memory
+;              = error_arena_trashed
+;
+        procedure   $ALLOC,NEAR
+        ASSUME  DS:NOTHING,ES:NOTHING
+
+        EnterCrit   critMem
+        XOR     AX,AX
+        MOV     DI,AX
+
+        MOV     [FirstArena],AX         ; init the options
+        MOV     [BestArena],AX
+        MOV     [LastArena],AX
+
+        PUSH    AX                      ; alloc_max <- 0
+        MOV     AX,[arena_head]         ; AX <- beginning of arena
+        CALL    Check_signature         ; ES <- AX, carry set if error
+        JC      alloc_err               ; IF error THEN GOTO err
+
+alloc_scan:
+        PUSH    ES
+        POP     DS                      ; DS <- ES
+        CMP     DS:[arena_owner],DI
+        JZ      alloc_free              ; IF current block is free THEN examine
+
+alloc_next:
+        CMP     BYTE PTR DS:[DI],arena_signature_end
+                                        ; IF current block is last THEN
+        JZ      alloc_end               ;   GOTO end
+        CALL    arena_next              ; AX, ES <- next block, Carry set if error
+        JNC     alloc_scan              ; IF no error THEN GOTO scan
+
+alloc_err:
+        POP     AX
+
+alloc_trashed:
+        LeaveCrit   critMem
+        error   error_arena_trashed
+
+alloc_end:
+        CMP     [FirstArena],0
+        JNZ     alloc_do_split
+
+alloc_fail:
+        invoke  get_user_stack
+        POP     BX
+        MOV     [SI].user_BX,BX
+        LeaveCrit   critMem
+        error   error_not_enough_memory
+
+alloc_free:
+        CALL    coalesce                ; add following free block to current
+        JC      alloc_err               ; IF error THEN GOTO err
+        MOV     CX,DS:[arena_size]
+
+        POP     DX                      ; check for max found size
+        CMP     CX,DX
+        JNA     alloc_test
+        MOV     DX,CX
+
+alloc_test:
+        PUSH    DX
+        CMP     BX,CX                   ; IF BX > size of current block THEN
+        JA      alloc_next              ;   GOTO next
+
+        CMP     [FirstArena],0
+        JNZ     alloc_best
+        MOV     [FirstArena],DS         ; save first one found
+alloc_best:
+        CMP     [BestArena],0
+        JZ      alloc_make_best         ; initial best
+        PUSH    ES
+        MOV     ES,[BestArena]
+        CMP     ES:[arena_size],CX      ; is size of best larger than found?
+        POP     ES
+        JBE     alloc_last
+alloc_make_best:
+        MOV     [BestArena],DS          ; assign best
+alloc_last:
+        MOV     [LastArena],DS          ; assign last
+        JMP     alloc_next
+
+;
+; split the block high
+;
+alloc_do_split_high:
+        MOV     DS,[LastArena]
+        MOV     CX,DS:[arena_size]
+        SUB     CX,BX
+        MOV     DX,DS
+        JE      alloc_set_owner         ; sizes are equal, no split
+        ADD     DX,CX                   ; point to next block
+        MOV     ES,DX                   ; no decrement!
+        DEC     CX
+        XCHG    BX,CX                   ; bx has size of lower block
+        JMP     alloc_set_sizes         ; cx has upper (requested) size
+
+;
+; we have scanned memory and have found all appropriate blocks
+; check for the type of allocation desired; first and best are identical
+; last must be split high
+;
+alloc_do_split:
+        CMP     BYTE PTR [AllocMethod], 1
+        JA      alloc_do_split_high
+        MOV     DS,[FirstArena]
+        JB      alloc_get_size
+        MOV     DS,[BestArena]
+alloc_get_size:
+        MOV     CX,DS:[arena_size]
+        SUB     CX,BX                   ; get room left over
+        MOV     AX,DS
+        MOV     DX,AX                   ; save for owner setting
+        JE      alloc_set_owner         ; IF BX = size THEN (don't split)
+        ADD     AX,BX
+        INC     AX                      ; remember the header
+        MOV     ES,AX                   ; ES <- DS + BX (new header location)
+        DEC     CX                      ; CX <- size of split block
+alloc_set_sizes:
+        MOV     DS:[arena_size],BX      ; current size <- BX
+        MOV     ES:[arena_size],CX      ; split size <- CX
+        MOV     BL,arena_signature_normal
+        XCHG    BL,DS:[DI]              ; current signature <- 4D
+        MOV     ES:[DI],BL              ; new block sig <- old block sig
+        MOV     ES:[arena_owner],DI
+
+alloc_set_owner:
+        MOV     DS,DX
+        MOV     AX,[CurrentPDB]
+        MOV     DS:[arena_owner],AX
+        MOV     AX,DS
+        INC     AX
+        POP     BX
+        LeaveCrit   critMem
+        transfer    SYS_RET_OK
+
+EndProc $alloc
+
+SUBTTL $SETBLOCK - change size of an allocated block (if possible)
+PAGE
+;
+;   Assembler usage:
+;           MOV     ES,block
+;           MOV     BX,newsize
+;           MOV     AH,setblock
+;           INT     21h
+;         if setblock fails for growing, BX will have the maximum
+;         size possible
+;   Error return:
+;           AX = error_invalid_block
+;              = error_arena_trashed
+;              = error_not_enough_memory
+;              = error_invalid_function
+;
+        procedure   $SETBLOCK,NEAR
+        ASSUME  DS:NOTHING,ES:NOTHING
+        EnterCrit   critMem
+        MOV     DI,arena_signature
+        MOV     AX,ES
+        DEC     AX
+        CALL    check_signature
+        JNC     setblock_grab
+
+setblock_bad:
+        JMP     alloc_trashed
+
+setblock_grab:
+        MOV     DS,AX
+        CALL    coalesce
+        JC      setblock_bad
+        MOV     CX,DS:[arena_size]
+        PUSH    CX
+        CMP     BX,CX
+        JBE     alloc_get_size
+        JMP     alloc_fail
+EndProc $setblock
+
+SUBTTL $DEALLOC - free previously allocated piece of memory
+PAGE
+;
+;   Assembler usage:
+;           MOV     ES,block
+;           MOV     AH,dealloc
+;           INT     21h
+;
+;   Error return:
+;           AX = error_invalid_block
+;              = error_arena_trashed
+;
+        procedure   $DEALLOC,NEAR
+        ASSUME  DS:NOTHING,ES:NOTHING
+        EnterCrit   critMem
+        MOV     DI,arena_signature
+        MOV     AX,ES
+        DEC     AX
+        CALL    check_signature
+        JC      dealloc_err
+        MOV     ES:[arena_owner],DI
+        LeaveCrit   critMem
+        transfer    SYS_RET_OK
+
+dealloc_err:
+        LeaveCrit   critMem
+        error   error_invalid_block
+EndProc $DEALLOC
+
+SUBTTL $AllocOper - get/set allocation mechanism
+PAGE
+;
+;   Assembler usage:
+;           MOV     AH,AllocOper
+;           MOV     BX,method
+;           MOV     AL,func
+;           INT     21h
+;
+;   Error return:
+;           AX = error_invalid_function
+;
+        procedure   $AllocOper,NEAR
+        ASSUME  DS:NOTHING,ES:NOTHING
+        CMP     AL,1
+        JB      AllocOperGet
+        JZ      AllocOperSet
+        MOV     EXTERR_LOCUS,errLoc_mem ; Extended Error Locus
+        error   error_invalid_function
+AllocOperGet:
+        MOV     AL,BYTE PTR [AllocMethod]
+        XOR     AH,AH
+        transfer    SYS_RET_OK
+AllocOperSet:
+        MOV     [AllocMethod],BL
+        transfer    SYS_RET_OK
+EndProc $AllocOper
+
+CODE    ENDS
+    END