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## compute the factorial of 5, and return the result in the exit code
#
# Uses syntax sugar for:
# rm32 operands
# function calls
# control flow
#
# To run:
# $ ./translate_subx init.linux [01]*.subx factorial.subx -o factorial
# $ bootstrap/bootstrap run factorial
# Expected result:
# $ echo $?
# 120
#
# You can also run the automated test suite:
# $ bootstrap/bootstrap run factorial test
# Expected output:
# ........
# Every '.' indicates a passing test. Failing tests get a 'F'.
#
# Compare factorial3.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
81 7/subop/compare *(ebp+8) 1/imm32
{
7f/jump-if-> break/disp8
b8/copy-to-eax 1/imm32
eb/jump $factorial:end/disp8
}
# n > 1; return n * factorial(n-1)
8b/-> *(ebp+8) 1/r32/ecx
49/decrement-ecx
(factorial %ecx) # => eax
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)
(check-ints-equal %eax 0x78 "F - test-factorial")
c3/return
Entry: # run tests if necessary, compute `factorial(5)` if not
# . prologue
89/<- %ebp 4/r32/esp
# initialize heap (needed by tests elsewhere)
(new-segment *Heap-size Heap)
# if (argc <= 1) return factorial(5)
{
# if (argc > 1) break
81 7/subop/compare *ebp 1/imm32
7f/jump-if-> break/disp8
# ebx = factorial(5)
(factorial 5) # => eax
89/<- %ebx 0/r32/eax
eb/jump $main:end/disp8
}
# otherwise if first arg is "test", then return run_tests()
{
# if (!kernel-string-equal?(argv[1], "test")) break
(kernel-string-equal? *(ebp+8) "test") # => eax
3d/compare-eax-and 0/imm32/false
74/jump-if-= break/disp8
#
(run-tests)
# exit(*Num-test-failures)
8b/-> *Num-test-failures 3/r32/ebx
eb/jump $main:end/disp8
}
bb/copy-to-ebx 0/imm32
$main:end:
e8/call syscall_exit/disp32
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