90 lines
2.1 KiB
Plaintext
90 lines
2.1 KiB
Plaintext
## compute the factorial of 5, and return the result in the exit code
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#
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# Uses syntax sugar for:
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# rm32 operands
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# function calls
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# control flow
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#
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# To run:
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# $ ./translate_subx init.linux 0*.subx apps/factorial.subx -o apps/factorial
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# $ ./subx run apps/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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# $ ./subx run apps/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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Entry: # run tests if necessary, compute `factorial(5)` if not
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# . prologue
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89/<- %ebp 4/r32/esp
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# initialize heap
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(new-segment *Heap-size Heap)
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# - if argc > 1, then return run_tests()
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{
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# if (argc <= 1) break
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81 7/subop/compare *ebp 1/imm32
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7e/jump-if-<= break/disp8
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# if (!kernel-string-equal?(argv[1], "test")) break
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(kernel-string-equal? *(ebp+8) "test") # => eax
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3d/compare-eax-and 0/imm32/false
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74/jump-if-= break/disp8
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#
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(run-tests)
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# eax = *Num-test-failures
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8b/-> *Num-test-failures 3/r32/ebx
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}
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# if (argc <= 1) factorial(5)
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{
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# if (argc > 1) break
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81 7/subop/compare *ebp 1/imm32
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7f/jump-if-> break/disp8
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# eax = factorial(5)
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(factorial 5)
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# syscall(exit, eax)
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89/<- %ebx 0/r32/eax
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}
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b8/copy-to-eax 1/imm32/exit
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cd/syscall 0x80/imm8
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factorial: # n : int -> int/eax
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# . prologue
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55/push-ebp
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89/<- %ebp 4/r32/esp
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# save registers
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53/push-ebx
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# if (n <= 1) return 1
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81 7/subop/compare *(ebp+8) 1/imm32
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{
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7f/jump-if-> break/disp8
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b8/copy-to-eax 1/imm32
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}
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# if (n > 1) return n * factorial(n-1)
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{
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7e/jump-if-<= break/disp8
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# var ebx : int = n-1
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8b/-> *(ebp+8) 3/r32/ebx
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4b/decrement-ebx
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(factorial %ebx) # => eax
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f7 4/subop/multiply-into-eax *(ebp+8)
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}
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# restore registers
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5b/pop-to-ebx
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# . epilogue
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89/<- %esp 5/r32/ebp
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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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(check-ints-equal %eax 0x78 "F - test-factorial")
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c3/return
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