arena memory example

mem-arena.tal

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+( alloc.tal )
+( )
+( simple arena allocator )
+( )
+( the idea here is to pre-allocate a large arena of memory )
+( and then keep a pointer to the first unallocated byte. )
+( memory is released in reverse order of when it was allocated. )
+( )
+( in this example we're preallocating 16,384 bytes (#4000) )
+( located at mem-arena. we're using mem-cursor to point to )
+( the next unallocated byte. )
+( )
+( if mem-cursor ever contains the address of mem-cursor it )
+( means we've reached the limit of what we can allocate. )
+( we raise divide-by-zero errors if we cannot allocate )
+( or release memory as requested. )
+( )
+( memory can be freed by size (number of bytes) or cleared )
+( all at once. )
+
+( macro to allocate one byte of memory )
+%mem-alloc-byte { #0001 ;mem-alloc JMP2r } ( -> addr* )
+
+( macro to allocate two bytes of memory )
+%mem-alloc-short { #0002 ;mem-alloc JMP2r } ( -> addr* )
+
+( macro to allocate an 8-bit count of memory (n) )
+%mem-alloc8 { #00 SWP ;mem-alloc JMP2r } ( n^ -> addr* )
+
+( macro to allocate a 16-bit count of memory (n) )
+%mem-alloc16 { ;mem-alloc JMP2r } ( n* -> addr* )
+
+|10 @Console [ &vector $2 &read $1 &pad $5 &write $1 ]
+
+|0100
+    ;mem-init JSR2
+    ;on-input .Console/vector DEO2
+    ;mem-cursor LDA2 ;start STA2
+    BRK
+
+@start $2
+
+@on-input
+    .Console/read DEI DUP ,&continue JCN
+    ( ;on-complete JSR2 ) POP BRK
+    &continue ( mem-alloc-byte STA ) BRK
+
+@on-complete
+    ;mem-cursor LDA2 STH2
+    ;start LDA2
+    &loop
+    DUP2 STH2kr LTH2 ,&continue JCN
+    ;mem-init JSR2 POP2 POP2r JMP2r
+    &continue
+    LDA2k .Console/write DEO
+    INC2 ,&loop JMP
+
+( allocate n bytes of memory )
+@mem-alloc ( n* -> addr* )
+    ;mem-cursor LDA2 ADD2 DUP2 ( new-addr new-addr )
+    ;mem-cursor LTH2 ,&ok JCN DIV2 #0000 ( fail if we reach mem-cursor's own address )
+    &ok DUP2 ;mem-cursor STA2 JMP2r
+
+( initialize memory, release all allocated memory )
+@mem-init ( -> )
+    ;mem-arena ;mem-cursor STA2 JMP2r
+
+( release n bytes of allocated memory )
+@mem-release ( n* -> )
+    ;mem-cursor LDA2 SUB2 DUP2 ( new-addr new-addr )
+    ;mem-arena LTH2 ,&fail JCN ;mem-cursor STA2 JMP2r
+    &fail DIV2 #0000 ( fail if we reach beyond mem-arena's own address )
+
+( location of the memory to be allocated )
+@mem-arena $4000
+
+( pointer to the next free byte, if any )
+@mem-cursor $2