55 lines
907 B
NASM
55 lines
907 B
NASM
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; All these functions assume DS=0
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malloc_reset:
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xor ax, ax
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mov es, ax
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call malloc_get_table
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mov cx, 0x100 ; 256 words
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rep stosw
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ret
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; Input:
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; 0:BX - ptr to mem paragraph
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; Output:
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; AL - bitmask for byte in table
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; BX - offset in table
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malloc_calc_offsets:
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; ch is bit offset
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; cl is operand for bit shifts
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push cx
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; strip last 4 bits (offset within paragraph)
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mov cl, 4
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shr bx, cl
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; backup the next 3 bits of bx (wll be bit offset)
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mov ch, bl
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and ch, 0x07
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; calculate byte offset by shifting off 3 bits
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mov cl, 3
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shr bx, cl
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; setup bit mask in al, shifted by bit offset
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mov al, 0x01
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mov cl, ch
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shl al, cl
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pop cx
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; fallthrough to setup DI
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malloc_get_table:
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mov di, 0x0600
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ret
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malloc_mark_allocated:
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call malloc_calc_offsets
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or byte [bx+di], al
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ret
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malloc_mark_free:
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call malloc_calc_offsets
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not al
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and byte [bx+di], al
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ret
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