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## compute the factorial of 5, and return the result in the exit code
#
# Uses syntax sugar for:
# rm32 operands
#
# To run:
# $ ./translate_subx init.linux [01]*.subx apps/factorial2.subx
# $ ./a.elf
# Expected result:
# $ echo $?
# 120
#
# You can also run the automated test suite:
# $ ./a.elf test
# Expected output:
# ........
# Every '.' indicates a passing test. Failing tests get a 'F'.
#
# Compare factorial.subx
== code
factorial: # n: int -> _/eax: int
# . prologue
55/push-ebp
89/<- %ebp 4/r32/esp
# save registers
51/push-ecx
# if (n <= 1) return 1
b8/copy-to-eax 1/imm32
81 7/subop/compare *(ebp+8) 1/imm32
7e/jump-if-<= $factorial:end/disp8
# n > 1; return n * factorial(n-1)
8b/-> *(ebp+8) 1/r32/ecx
49/decrement-ecx
# var tmp/eax: int = factorial(n-1)
# . . push args
51/push-ecx
# . . call
e8/call factorial/disp32
# . . discard args
81 0/subop/add %esp 4/imm32
# return n * tmp
f7 4/subop/multiply-into-eax *(ebp+8)
# TODO: check for overflow
$factorial:end:
# restore registers
59/pop-to-ecx
# . epilogue
89/<- %esp 5/r32/ebp
5d/pop-to-ebp
c3/return
test-factorial:
# factorial(5)
# . . push args
68/push 5/imm32
# . . call
e8/call factorial/disp32
# . . discard args
81 0/subop/add %esp 4/imm32
# check-ints-equal(eax, 120, msg)
# . . push args
68/push "F - test-factorial"/imm32
68/push 0x78/imm32/expected-120
50/push-eax
# . . call
e8/call check-ints-equal/disp32
# . . discard args
81 0/subop/add %esp 0xc/imm32
# end
c3/return
Entry: # run tests if necessary, compute `factorial(5)` if not
# . prologue
89/<- %ebp 4/r32/esp
# initialize heap (needed by tests elsewhere)
# . Heap = new-segment(Heap-size)
# . . push args
68/push Heap/imm32
ff 6/subop/push *Heap-size
# . . call
e8/call new-segment/disp32
# . . discard args
81 0/subop/add %esp 8/imm32
# if (argc <= 1) return factorial(5)
81 7/subop/compare *ebp 1/imm32
7f/jump-if-> $main:run-tests/disp8
# . . push args
68/push 5/imm32
# . . call
e8/call factorial/disp32
# . . discard args
81 0/subop/add %esp 4/imm32
# .
89/<- %ebx 0/r32/eax
eb/jump $main:end/disp8
$main:run-tests:
# otherwise if first arg is "test", then return run_tests()
# if (!kernel-string-equal?(argv[1], "test")) goto do-nothing
# . eax = kernel-string-equal?(argv[1], "test")
# . . push args
68/push "test"/imm32
ff 6/subop/push *(ebp+8)
# . . call
e8/call kernel-string-equal?/disp32
# . . discard args
81 0/subop/add %esp 8/imm32
# . if (eax == false) goto do-nothing
3d/compare-eax-and 0/imm32/false
74/jump-if-= $main:do-nothing/disp8
# run-tests()
e8/call run-tests/disp32
# exit(*Num-test-failures)
8b/-> *Num-test-failures 3/r32/ebx
eb/jump $main:end/disp8
$main:do-nothing:
bb/copy-to-ebx 0/imm32
$main:end:
e8/call syscall_exit/disp32
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