5706 - example at different levels of syntax sugar

Thanks Mateusz Czapliński for the feedback:
  https://lobste.rs/s/xtxlec/mu_minimal_hobbyist_computing_stack#c_1mzq94

1 files changed, 115 insertions, 0 deletions

diff --git a/apps/factorial2.subx b/apps/factorial2.subx
new file mode 100644
index 00000000..af2f3eea
--- /dev/null
+++ b/apps/factorial2.subx
@@ -0,0 +1,115 @@
+## compute the factorial of 5, and return the result in the exit code
+#
+# To run:
+#   $ ./ntranslate 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
+    # . Heap = new-segment(Heap-size)
+    # . . push args
+    68/push Heap/imm32
+    68/push Heap-size/imm32
+    # . . call
+    e8/call new-segment/disp32
+    # . . discard args
+    81 0/subop/add %esp 8/imm32
+
+    # - 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-lesser-or-equal $run-main/disp8
+    # if (!kernel-string-equal?(argv[1], "test")) goto run-main
+    # . 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 == 0) goto run-main
+    3d/compare-eax-and 0/imm32
+    74/jump-if-equal $run-main/disp8
+    # run-tests()
+    e8/call run-tests/disp32
+    # syscall(exit, *Num-test-failures)
+    8b/-> *Num-test-failures 3/r32/ebx
+    eb/jump $main:end/disp8
+$run-main:
+    # - otherwise return factorial(5)
+    # eax = factorial(5)
+    # . . push args
+    68/push 5/imm32
+    # . . call
+    e8/call factorial/disp32
+    # . . discard args
+    81 0/subop/add %esp 4/imm32
+    # 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
+    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-<= $factorial:end/disp8
+    # ebx = n-1
+    8b/-> *(ebp+8) 3/r32/ebx
+    4b/decrement-ebx
+    # eax = factorial(n-1)
+    # . . push args
+    53/push-ebx
+    # . . call
+    e8/call factorial/disp32
+    # . . discard args
+    81 0/subop/add %esp 4/imm32
+    # return n * factorial(n-1)
+    f7 4/subop/multiply-into-eax *(ebp+8)
+    # TODO: check for overflow
+$factorial:end:
+    # . epilogue
+    5b/pop-to-ebx
+    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