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53 lines
1.2 KiB
53 lines
1.2 KiB
# array of 2 integers (each size 4 bytes)
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# load address of flag into fx register
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# access flag[] with 0(%fx,%index,4)
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# where %index is a register holding 0 or 1
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# index reg contains 0 -> flag[0], if 1->flag[1]
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.var flag 2
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# global turn variable
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.var turn
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# global count
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.var count
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.main
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# put address of flag into fx
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lea flag, %fx
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# assume thread ID is in bx (0 or 1, scale by 4 to get proper flag address)
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mov %bx, %cx # bx: self, now copies to cx
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neg %cx # cx: - self
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add $1, %cx # cx: 1 - self
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.acquire
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mov $1, 0(%fx,%bx,4) # flag[self] = 1
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mov %cx, turn # turn = 1 - self
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.spin1
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mov 0(%fx,%cx,4), %ax # flag[1-self]
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test $1, %ax
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jne .fini # if flag[1-self] != 1, skip past loop to .fini
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.spin2 # just labeled for fun, not needed
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mov turn, %ax
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test %cx, %ax # compare 'turn' and '1 - self'
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je .spin1 # if turn==1-self, go back and start spin again
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# fall out of spin
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.fini
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# do critical section now
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mov count, %ax
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add $1, %ax
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mov %ax, count
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.release
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mov $0, 0(%fx,%bx,4) # flag[self] = 0
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# end case: make sure it's other's turn
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mov %cx, turn # turn = 1 - self
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halt
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