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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
#
# To run:
# $ ./translate_subx init.linux 0*.subx apps/factorial.subx -o apps/factorial
# $ ./subx run apps/factorial
# Expected result:
# $ echo $?
# 120
#
# You can also run the automated test suite:
# $ ./subx run apps/factorial test
# Expected output:
# ........
# Every '.' indicates a passing test. Failing tests get a 'F'.
== code
Entry: # run tests if necessary, compute `factorial(5)` if not
# . prologue
89/<- %ebp 4/r32/esp
# initialize heap
(new-segment *Heap-size Heap)
# - if argc > 1 and argv[1] == "test", then return run_tests()
# if (argc <= 1) goto run-main
81 7/subop/compare *ebp 1/imm32
7e/jump-if-<= $run-main/disp8
# if (!kernel-string-equal?(argv[1], "test")) goto run-main
(kernel-string-equal? *(ebp+8) "test") # => eax
# . if (eax == false) goto run-main
3d/compare-eax-and 0/imm32/false
74/jump-if-= $run-main/disp8
#
(run-tests)
# syscall(exit, *Num-test-failures)
8b/-> *Num-test-failures 3/r32/ebx
eb/jump $main:end/disp8
$run-main:
# - otherwise
(factorial 5) # => eax
# syscall(exit, eax)
89/<- %ebx 0/r32/eax
$main:end:
b8/copy-to-eax 1/imm32/exit
cd/syscall 0x80/imm8
factorial: # n: int -> int/eax
# . prologue
55/push-ebp
89/<- %ebp 4/r32/esp
# save registers
53/push-ebx
# 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
# var ebx: int = n-1
8b/-> *(ebp+8) 3/r32/ebx
4b/decrement-ebx
#
(factorial %ebx) # => eax
# return n * factorial(n-1)
f7 4/subop/multiply-into-eax *(ebp+8)
# TODO: check for overflow
$factorial:end:
# restore registers
5b/pop-to-ebx
# . 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
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