2018-09-01 17:04:58 +00:00
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## compute the factorial of 5, and return the result in the exit code
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#
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2019-07-31 22:28:23 +00:00
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# To run:
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2020-03-07 02:07:39 +00:00
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# $ ./bootstrap translate init.linux 0*.subx apps/factorial.subx -o apps/factorial
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# $ ./bootstrap run apps/factorial
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2018-09-01 17:04:58 +00:00
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# Expected result:
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# $ echo $?
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# 120
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2018-09-22 06:52:48 +00:00
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#
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2018-09-24 04:01:28 +00:00
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# You can also run the automated test suite:
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2020-03-07 02:07:39 +00:00
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# $ ./bootstrap run apps/factorial test
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2018-09-22 06:52:48 +00:00
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# Expected output:
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2018-09-24 04:01:28 +00:00
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# ........
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2018-09-22 06:52:48 +00:00
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# Every '.' indicates a passing test. Failing tests get a 'F'.
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2018-09-01 17:04:58 +00:00
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2018-09-01 22:58:53 +00:00
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== code
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2018-11-30 19:10:44 +00:00
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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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2018-09-01 17:04:58 +00:00
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2019-02-19 05:48:19 +00:00
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Entry: # run tests if necessary, compute `factorial(5)` if not
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2019-10-16 02:35:19 +00:00
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# . prologue
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2019-09-01 05:18:24 +00:00
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89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
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2019-05-26 06:47:49 +00:00
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# initialize heap
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2019-09-19 23:32:10 +00:00
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# . Heap = new-segment(Heap-size)
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2019-05-26 06:47:49 +00:00
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# . . push args
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68/push Heap/imm32
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2019-11-30 19:14:49 +00:00
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ff 6/subop/push 0/mod/indirect 5/rm32/.disp32 . . . Heap-size/disp32 # push *Heap-size
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2019-05-26 06:47:49 +00:00
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# . . call
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e8/call new-segment/disp32
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# . . discard args
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2019-08-26 18:55:26 +00:00
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
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2019-02-19 05:48:19 +00:00
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2019-02-15 00:24:20 +00:00
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# - if argc > 1 and argv[1] == "test", then return run_tests()
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2019-09-01 05:18:24 +00:00
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# if (argc <= 1) goto run-main
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2019-08-26 18:55:26 +00:00
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81 7/subop/compare 1/mod/*+disp8 5/rm32/ebp . . . . 0/disp8 1/imm32 # compare *ebp
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2020-01-17 02:31:12 +00:00
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7e/jump-if-<= $run-main/disp8
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2019-09-01 05:18:24 +00:00
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# if (!kernel-string-equal?(argv[1], "test")) goto run-main
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# . eax = kernel-string-equal?(argv[1], "test")
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2018-11-30 19:10:44 +00:00
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# . . push args
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2018-11-30 18:54:42 +00:00
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68/push "test"/imm32
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2019-08-26 18:55:26 +00:00
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ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8)
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2018-11-30 19:10:44 +00:00
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# . . call
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2019-01-16 19:13:39 +00:00
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e8/call kernel-string-equal?/disp32
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2018-11-30 19:10:44 +00:00
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# . . discard args
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2019-08-26 18:55:26 +00:00
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
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2019-12-08 21:56:46 +00:00
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# . if (eax == false) goto run-main
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3d/compare-eax-and 0/imm32/false
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2020-01-17 02:31:12 +00:00
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74/jump-if-= $run-main/disp8
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2019-09-01 05:18:24 +00:00
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# run-tests()
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2018-11-30 18:54:42 +00:00
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e8/call run-tests/disp32
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2019-09-02 06:57:29 +00:00
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# syscall(exit, *Num-test-failures)
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2019-09-01 06:22:49 +00:00
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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 $main:end/disp8
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2018-10-06 02:49:47 +00:00
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$run-main:
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2019-05-21 05:14:37 +00:00
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# - otherwise return factorial(5)
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2019-09-02 06:57:29 +00:00
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# eax = factorial(5)
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2018-11-30 19:10:44 +00:00
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# . . push args
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2018-11-30 18:54:42 +00:00
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68/push 5/imm32
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2018-11-30 19:10:44 +00:00
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# . . call
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2018-11-30 18:54:42 +00:00
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e8/call factorial/disp32
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2018-11-30 19:10:44 +00:00
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# . . discard args
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2019-08-26 18:55:26 +00:00
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
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# syscall(exit, eax)
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89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx
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2019-09-01 06:22:49 +00:00
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$main:end:
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2019-08-26 18:55:26 +00:00
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b8/copy-to-eax 1/imm32/exit
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2018-11-30 18:54:42 +00:00
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cd/syscall 0x80/imm8
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2018-09-01 17:04:58 +00:00
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2020-01-27 08:36:44 +00:00
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factorial: # n: int -> int/eax
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2019-10-16 02:35:19 +00:00
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# . prologue
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2019-08-26 18:55:26 +00:00
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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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53/push-ebx
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2019-09-01 05:34:56 +00:00
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# if (n <= 1) return 1
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2019-08-26 18:55:26 +00:00
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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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2018-11-30 18:54:42 +00:00
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7e/jump-if-<= $factorial:end/disp8
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2020-01-27 08:36:44 +00:00
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# var ebx: int = n-1
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2019-08-26 18:55:26 +00:00
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8b/copy 1/mod/*+disp8 5/rm32/ebp . . 3/r32/ebx 8/disp8 . # copy *(ebp+8) to ebx
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2019-10-03 07:15:08 +00:00
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4b/decrement-ebx
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2020-01-27 08:36:44 +00:00
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# var eax: int = factorial(n-1)
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2018-11-30 19:10:44 +00:00
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# . . push args
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2019-08-26 18:55:26 +00:00
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53/push-ebx
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2018-11-30 19:10:44 +00:00
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# . . call
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2018-11-30 18:54:42 +00:00
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e8/call factorial/disp32
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2018-11-30 19:10:44 +00:00
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# . . discard args
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2019-08-26 18:55:26 +00:00
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
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2018-11-30 18:54:42 +00:00
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# return n * factorial(n-1)
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2019-08-26 18:55:26 +00:00
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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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2018-11-30 18:54:42 +00:00
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# TODO: check for overflow
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2018-10-17 06:02:42 +00:00
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$factorial:end:
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2019-10-16 02:35:19 +00:00
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# . epilogue
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2019-08-26 18:55:26 +00:00
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5b/pop-to-ebx
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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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2018-11-30 18:54:42 +00:00
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c3/return
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2018-09-01 17:04:58 +00:00
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2018-10-06 02:49:47 +00:00
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test-factorial:
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2018-11-30 18:54:42 +00:00
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# factorial(5)
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2018-11-30 19:10:44 +00:00
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# . . push args
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2018-11-30 18:54:42 +00:00
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68/push 5/imm32
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2018-11-30 19:10:44 +00:00
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# . . call
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2018-11-30 18:54:42 +00:00
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e8/call factorial/disp32
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2018-11-30 19:10:44 +00:00
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# . . discard args
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2019-08-26 18:55:26 +00:00
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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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2018-11-30 19:10:44 +00:00
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# . . push args
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2018-11-30 18:54:42 +00:00
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68/push "F - test-factorial"/imm32
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68/push 0x78/imm32/expected-120
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2019-08-26 18:55:26 +00:00
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50/push-eax
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2018-11-30 19:10:44 +00:00
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# . . call
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2018-11-30 18:54:42 +00:00
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e8/call check-ints-equal/disp32
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2018-11-30 19:10:44 +00:00
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# . . discard args
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2019-08-26 18:55:26 +00:00
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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2018-11-30 18:54:42 +00:00
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# end
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c3/return
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2018-09-23 18:17:11 +00:00
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2018-11-30 19:10:44 +00:00
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# . . vim:nowrap:textwidth=0
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