154 lines
7.2 KiB
Plaintext
154 lines
7.2 KiB
Plaintext
## compute the factorial of 5, and print the result
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#
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# To run:
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# $ bootstrap/bootstrap translate [01]*.subx factorial.subx -o factorial
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# $ bootstrap/bootstrap run factorial
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# Expected result:
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# $ echo $?
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# 120
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#
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# You can also run the automated test suite:
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# $ bootstrap/bootstrap run factorial test
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# Expected output:
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# ........
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# Every '.' indicates a passing test. Failing tests get a 'F'.
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== code
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# instruction effective address register displacement immediate
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# . op subop mod rm32 base index scale r32
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# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes
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factorial: # n: int -> _/eax: int
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# . prologue
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55/push-ebp
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89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
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51/push-ecx
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# if (n <= 1) return 1
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b8/copy-to-eax 1/imm32
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81 7/subop/compare 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 1/imm32 # compare *(ebp+8)
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7e/jump-if-<= $factorial:end/disp8
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# var ecx: int = n-1
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8b/copy 1/mod/*+disp8 5/rm32/ebp . . 1/r32/ecx 8/disp8 . # copy *(ebp+8) to ecx
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49/decrement-ecx
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# var eax: int = factorial(n-1)
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# . . push args
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51/push-ecx
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# . . call
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e8/call factorial/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
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# return n * factorial(n-1)
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f7 4/subop/multiply 1/mod/*+disp8 5/rm32/ebp . . 8/disp8 . # multiply *(ebp+8) into eax
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# TODO: check for overflow
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$factorial:end:
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# restore registers
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59/pop-to-ecx
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# . epilogue
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89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
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5d/pop-to-ebp
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c3/return
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test-factorial:
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# factorial(5)
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# . . push args
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68/push 5/imm32
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# . . call
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e8/call factorial/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
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# check-ints-equal(eax, 120, msg)
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# . . push args
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68/push "F - test-factorial"/imm32
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68/push 0x78/imm32/expected-120
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50/push-eax
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# . . call
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e8/call check-ints-equal/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# end
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c3/return
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Entry: # run tests if necessary, compute `factorial(5)` if not
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# . prologue
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89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
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# initialize heap (needed by tests elsewhere)
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# . Heap = new-segment(Heap-size)
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# . . push args
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68/push Heap/imm32
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ff 6/subop/push 0/mod/indirect 5/rm32/.disp32 . . . Heap-size/disp32 # push *Heap-size
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# . . call
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e8/call new-segment/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
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# if (argc <= 1) return factorial(5)
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$run-main:
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81 7/subop/compare 1/mod/*+disp8 5/rm32/ebp . . . . 0/disp8 1/imm32 # compare *ebp
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7f/jump-if-> $main:run-tests/disp8
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# eax = factorial(5)
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# . . push args
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68/push 5/imm32
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# . . call
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e8/call factorial/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
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# var buffer/ecx: (stream byte 10) # number of decimal digits a 32-bit number can have
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81 5/subop/subtract 3/mod/direct 4/rm32/esp . . . . . 0xa/imm32 # subtract from esp
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68/push 0xa/imm32/decimal-digits-in-32bit-number
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68/push 0/imm32/read
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68/push 0/imm32/write
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89/copy 3/mod/direct 1/rm32/ecx . . . 4/r32/esp . . # copy esp to ecx
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# write-int32-decimal(buffer, eax)
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# . . push args
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50/push-eax
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51/push-ecx
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# . . call
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e8/call write-int32-decimal/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
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# write-stream(stderr, buffer)
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# . . push args
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51/push-ecx
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68/push 2/imm32/stderr
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# . . call
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e8/call write-stream/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
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# write(stderr, Newline)
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# . . push args
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68/push Newline/imm32
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68/push 2/imm32/stderr
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# . . call
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e8/call write/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
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#
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89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx
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eb/jump $main:end/disp8
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$main:run-tests:
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# otherwise if first arg is "test", then return run_tests()
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# if (!kernel-string-equal?(argv[1], "test")) goto do-nothing
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# . eax = kernel-string-equal?(argv[1], "test")
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# . . push args
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68/push "test"/imm32
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ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8)
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# . . call
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e8/call kernel-string-equal?/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
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# . if (eax == false) goto do-nothing
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3d/compare-eax-and 0/imm32/false
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74/jump-if-= $main:do-nothing/disp8
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# run-tests()
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e8/call run-tests/disp32
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# exit(*Num-test-failures)
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8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/ebx Num-test-failures/disp32 # copy *Num-test-failures to ebx
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eb/jump $main:end/disp8
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$main:do-nothing:
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bb/copy-to-ebx 0/imm32
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$main:end:
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e8/call syscall_exit/disp32
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# . . vim:nowrap:textwidth=0
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