nxu/alloc.tal

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( alloc.tal )
( )
( SUMMARY )
( )
( this code can be used to dynamically claim and release memory. )
( )
( OVERVIEW )
( )
( memory is allocated using arenas which track which memory is free )
( and which memory is allocated. each arena can allocate items of a )
( fixed size (k bytes), and these arenas are configured at program )
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( start using ;init-arena. )
( )
( an arena that can allocate n items of k bytes each has an overhead )
( of ceil(n/8)+6 bytes; it will occuppy n*k+ceil(n/8)+6 bytes total. )
( )
( each slot of memory of size k is tracked using 1 bit in the header's )
( bitset. we will "mark" the slot using 1 when the memory is allocated )
( and we will "free" the slot using 0 when the memory is free and )
( ready to be used again. )
( )
( this system has no means of compacting memory in use to maximize )
( contiguous free memory. however the entire arena can be efficiently )
( cleared in a single operation. )
( )
( ARENA LAYOUT )
( )
( ADDR SIZE DESCRIPTION )
( a 2 bytes item size (k) )
( a+2 2 bytes next-arena-addr (a+t) )
( a+4 2 bytes data-addr (a+6+h) )
( a+6 ceil(n/8) bytes header bitset (h = n bits) )
( a+6+h nk bytes n item slots )
( a+6+h+nk ... (next arena starts here) )
( )
( MAJOR WORDS )
( )
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( NAME EFFECT DESCRIPTION )
( init-arena n* k* -> arena* create arena holding n k-byte slots )
( clear-arena arena* -> free all memory in the given arena )
( alloc arena* -> addr* allocate one slot of the given arena )
( alloc-of k* -> addr* find k-byte arena and allocate slot )
( free addr* -> find the given slot and free it )
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( ERROR DETECTION )
( )
( words that return arenas or addresses typically use 0000 or ffff to )
( signal errors. however, some words (such as free) will silently fail )
( if given invalid arguments. passing an invalid arena address will )
( likely corrupt your program's memory. )
( store up to n k-byte items )
( )
( total memory usage: n * k + ceil(n/8) + 6 )
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( )
( returns 0000 if allocated region is larger than remaining space )
@init-arena ( n* k* -> arena* )
DUP2 ,&k STR2 ( n k )
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OVR2 #0007 ADD2 #03 SFT2 DUP2 ,&h STR2 ( n k h )
STH2 ( n k [h] )
MUL2 STH2r ADD2 ( nk+h )
#0006 ADD2 ,&t STR2 ( ; t <- nk+h+6 )
;arena-pos LDA2 DUP2 ,&t LDR2 ADD2 GTH2k ,&toobig JCN ( a0 a1=a0+t )
DUP2 ;arena-pos STA2 ( a0 a1 )
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SWP2 STH2k INC2 INC2 STA2 ( [a0] ; a0+2<-a1 )
,&k LDR2 STH2kr STA2 ( [a0] ; a0<-k )
STH2kr ,&h LDR2 ADD2 #0006 ADD2 STH2kr #0004 ADD2 STA2 ( [a0] ; a0+4<-a0+6+h )
STH2r JMP2r ( a0 )
&toobig POP2 POP2 POP2 POP2 POP2 #0000 JMP2r ( 0000 )
[ &k $2 &h $2 &t $2 ]
( free all slots in the given arena )
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( )
( if an invalid arena is provided corruption will occur )
@clear-arena ( arena* -> )
DUP2 ;arena-data JSR2 STH2 ( arena [data] )
;arena-header JSR2 STH2 ( [data header] )
#00 ( 00 [limit pos] )
&loop ( 00 [limit pos] )
GTH2kr STHr ,&ok JCN ( 00 [limit pos] )
,&done JMP ( 00 [limit pos] )
&ok ( 00 [limit pos] )
DUP STH2kr STA INC2r ( 00 [limit pos+1] )
,&loop JMP ( 00 [limit pos+1] )
&done ( 00 [limit pos] )
POP POP2r POP2r JMP2r ( )
( allocate one slot of the given arena )
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( )
( returns 0000 if allocation fails )
@alloc ( arena* -> addr* )
DUP2 ;find-open-slot JSR2 ( arena index )
DUP2 #ffff EQU2 ,&failed JCN ( arena index )
OVR2 OVR2 ;mark-slot JSR2 ( arena index )
STH2 DUP2 ;arena-item JSR2 STH2r MUL2 ( arena index*k )
SWP2 ;arena-data JSR2 ADD2 JMP2r ( data+index*k )
&failed DUP2 EOR2 JMP2r ( 0000 )
( allocate one k-byte slot, finding the appropraite arena )
( )
( this word will fail if a k-byte arena wasn't already initialized )
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( )
( returns 00000 if allocation fails )
@alloc-of ( k* -> addr* )
;find-arena JSR2 ORAk ( arena* arena-is-zero^ )
,&ok JCN JMP2r ( 0000 )
&ok ;alloc JMP2 ( addr* )
( free the slot corresponding to the given address )
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( if the address is not part of an arena this word does nothing )
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( )
( if an unmanaged address is provided nothing will happen )
@free ( addr* -> )
;find-addr JSR2
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ORAk #00 EQU ,&skip JCN
;erase-slot JMP2
&skip POP2 JSR2
( reading metadata from the arena )
@arena-item ( arena* -> k* ) LDA2 JMP2r
@arena-next ( arena* -> addr* ) INC2 INC2 LDA2 JMP2r
@arena-data ( arena* -> addr* ) #0004 ADD2 LDA2 JMP2r
@arena-header ( arena* -> addr* ) #0006 ADD2 JMP2r
( find the arena for item size k, if any. )
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( )
( returns 0000 if no arena can be found )
@find-arena ( k* -> arena* )
STH2 ;arena-pos LDA2 ;arenas ( end* arena0* [k*] )
&loop ( end* arena )
GTH2k #00 EQU ,&notfound JCN ( end* arena* )
LDA2k STH2kr EQU2 ,&found JCN ( end* arena* [k*] )
;arena-next JSR2 ,&loop JCN ( end* next* [k*] )
&found ( end* arena* [k*] )
POP2r NIP2 JMP2r ( arena* )
&notfound ( end* addr* [k*] )
POP2r POP2 POP2 #0000 JMP2r ( 0000 )
( find the arena and slot index (if any) for the given address )
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( )
( returns 0000 0000 if address does not belong to an arena )
@find-addr ( addr* -> arena* index* )
STH2 ;arena-pos LDA2 ;arenas ( end* arena0* [addr*] )
&loop ( end* arena [addr*] )
GTH2k #00 EQU ,&notfound JCN ( end* arena* [addr*] )
DUP2 ;arena-data JSR2 ( end* arena* start* [addr*] )
STH2kr GTH2 ,&notfound JCN ( end* arena* [addr*] )
DUP2 ;arena-next JSR2 ( end* arena* next* [addr*] )
DUP2 STH2kr GTH2 ,&found JCN ( end* arena* next* [addr*] )
NIP2 ,&loop JCN ( end* next* [addr*] )
&found ( end* arena* next* [addr*] )
POP2 NIP2 ( arena* [addr*] )
DUP2 ;arena-data JSR2 STH2r ( arena* start* addr* )
SWP2 SUB2 ( arena* delta*=addr-start )
OVR2 LDA2 DIV2 JMP2r ( arena* slot*=delta/k )
&notfound ( end* arena* [addr*] )
POP2r POP2 DUP2 EOR2 DUP2 JMP2r ( 0000 0000 )
( finds the index of the first open slot, if any )
( )
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( returns the index of the slot )
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( if all slots are full returns ffff )
@find-open-slot ( arena* -> index* )
STH2k ;arena-data JSR2 ( data [a] )
STH2r ;arena-header JSR2 ( data h )
LIT2r 0008 LIT2r 0000 ( data h [8 0] )
&loop ( data h [8 i] )
GTH2k #00 EQU ,&failed JCN ( data h [8 i] )
LDAk #ff NEQ ,&found JCN ( data h [8 i] )
INC2 OVR2r ADD2r ( data h [8 i+8] )
,&loop JMP ( data h [8 i+8] )
&failed ( data header [8 i] )
POP2 POP2 POP2r POP2r ( )
#ffff JMP2r ( 0000 )
&found ( data h [8 i] )
NIP2 NIP2r LDA ( bits [i] )
#80 SWP ( 80 bits [i] )
&loop2 ( 80 bits [i] )
GTHk ,&done2 JCN ( 80 bits [i] )
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DUP ADD INC2r ,&loop2 JMP ( 80 bits<<1 [i+1] )
&done2 ( 80 _ [index] )
POP2 STH2r JMP2r ( index )
( mark a given slot in the arena as allocated )
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( )
( corruption will occur if an invalid arena or index are provided )
@mark-slot ( arena* index* -> )
SWP2 OVR2 ( index* arena* index* )
#03 SFT2 ADD2 #0006 ADD2 STH2 ( index* [addr*=arena+index/8] )
#0007 AND2 NIP #80 SWP SFT ( bit^=80>>(index&7) [addr*] )
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LDAkr STHr ORA ( new^=old|bit [addr*] )
STH2r STA JMP2r ( )
( deallocate a given slot in the arena )
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( )
( corruption will occur if an invalid arena or index are provided )
@erase-slot ( arena* index* -> )
SWP2 OVR2 ( index* arena* index* )
#03 SFT2 ADD2 #0006 ADD2 STH2 ( index* [addr*=arena+index/8] )
#ff7f SWP2 #0007 AND2 NIP ( ff7f sh^=(index&7) [addr*] )
SFT2 NIP ( mask^=ff7f>>sh [addr*] )
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LDAkr STHr AND ( new^=old&mask [addr*] )
STH2r STA JMP2r ( )
( keeps track of the limit of our arenas )
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( this will be the memory address of the next arena )
@arena-pos :arenas
( the starting point of all arenas )
( )
( memory addresses before this point are guaranteed )
( not to belong to any arena. )
@arenas