rdos/heap.asm

verbose_malloc:
  call malloc
  push si ; both backup and input value for kprintf
  mov si,.fmt
  call kprintf
  pop si
  ret
.fmt:
  db "malloc %X", 0

; Allocates memory on the kernel heap
; Strategy: smallest fit
; in	cx	size in bytes
; out	si	pointer
;
; Header:
;	word	ptr to next item (this implies its size)
;	byte	00 = free, >0 used (refcount)
malloc:
  push ax
  mov si,heap
  jmp .check
.next:
  mov si,[si]
.check:
  mov ax,[si]
  test ax,0xFFFF
  jz .append ; we are on last entry
  cmp byte [si+2],0x00
  jne .next ; entry is in use
  sub ax,cx
  je .reuse ; entry has exact length
  jc .next ; entry too short
  jmp .next ; we'd have to split, not implemented yet
.reuse: ; exact length
  mov byte [si+2],0xFF
  jmp .end
.append: ; append to last item
  mov ax, si
  add ax, 3
  add ax, cx
  mov word [si], ax
  mov byte [si+2], 0xFF
  push si
  mov word si,[si]
  mov byte [si],0x0000
  pop si
.end:
  add si, 0x03
  pop ax
  ret

; Deallocates memory on the kernel heap
free: