85 lines
1.4 KiB
NASM
85 lines
1.4 KiB
NASM
heap_size:
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; 1 step here means 1 byte heap alloc table + 16 byte heap data
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; 0x0400 = 1kB table, 16kb data
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dw 0x0400
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heap_init:
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push ax ; byte value (0)
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push cx ; loop counter
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push di ; target ptr
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push es
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mov ax, cs
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mov es, ax
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xor ax, ax
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mov cx, [heap_size]
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mov di, heap
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rep stosb ; rep makes this loop cx times, incrementing di, writing al
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pop es
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pop di
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pop cx
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pop ax
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ret
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; in ax number of bytes to alloc
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; out ds:di
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malloc:
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push cx ; number of blocks to allocate
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push bp ; base offset for block table
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push es
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; transfer 12 MSB from ax to cx
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add ax, 0x000F
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mov cl, 0x04
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shr ax, cl
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mov cx, ax
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mov bp, heap
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mov di, 0x0000
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mov ax, ds
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mov es, ax
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xor ah, ah ; we use ax for reading from al once
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jmp .firstblock
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.testlength:
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push cx
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push di
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add di, bp ; scasb doesn't add bp on its own
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repe scasb
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pop di
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pop cx
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je .found
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; find next free item
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mov al, 0x01
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.nextblock:
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add di, ax
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.firstblock:
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mov al, [bp+di]
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cmp al, 0x00
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jne .nextblock
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cmp cx, 0x0001 ; fast case: 1 block allocation, skip test if length fits
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jne .testlength
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.found:
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mov [bp+di], cl
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mov cl, 0x04
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shl di, cl
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add di, bp
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add di, [heap_size]
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pop es
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pop bp
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pop cx
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ret
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; in ds:di begin of data block to free (di trashed)
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free:
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push cx
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push bp
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mov bp, heap
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sub di, [heap_size]
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sub di, bp
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mov cl, 0x04
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shr di, cl
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mov byte [bp+di], 0x00
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pop bp
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pop cx
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ret
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