# Port of https://github.com/akkartik/crenshaw/blob/master/tutor2.1.pas
# which corresponds to the section "single digits" in https://compilers.iecc.com/crenshaw/tutor2.txt
# except that we support hex digits.
#
# To run (from the subx/ directory):
#   $ ./subx translate *.subx apps/crenshaw2-1.subx -o apps/crenshaw2-1
#   $ echo '3'  |./subx run apps/crenshaw2-1
# Expected output:
#   # syscall(exit, 3)
#   bb/copy-to-EBX  3/imm32
#   b8/copy-to-EAX  1/imm32/exit
#   cd/syscall  0x80/imm8
#
# To run the generated output:
#   $ echo '3'  |./subx run apps/crenshaw2-1 > z1.subx
#   $ ./subx translate z1.subx -o z1
#   $ ./subx run z1
#   $ echo $?
#   3
#
# Stdin must contain just a single hex digit. Other input will print an error:
#   $ echo 'xyz'  |./subx run apps/crenshaw2-1
#   Error: integer expected
#
# Names in this file sometimes follow Crenshaw's original rather than my usual
# naming conventions.

== code
#   instruction                     effective address                                                   register    displacement    immediate
# . op          subop               mod             rm32          base        index         scale       r32
# . 1-3 bytes   3 bits              2 bits          3 bits        3 bits      3 bits        2 bits      2 bits      0/1/2/4 bytes   0/1/2/4 bytes

Entry:  # run tests if necessary, call 'compile' if not
    # initialize heap
    # . Heap = new-segment(64KB)
    # . . push args
    68/push  Heap/imm32
    68/push  0x10000/imm32/64KB
    # . . call
    e8/call  new-segment/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP

    # . prolog
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # - if argc > 1 and argv[1] == "test", then return run_tests()
    # . argc > 1
    81          7/subop/compare     1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0/disp8         1/imm32           # compare *EBP
    7e/jump-if-lesser-or-equal  $run-main/disp8
    # . argv[1] == "test"
    # . . push args
    68/push  "test"/imm32
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         .                 # push *(EBP+8)
    # . . call
    e8/call  kernel-string-equal?/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # . check result
    3d/compare-EAX-and  1/imm32
    75/jump-if-not-equal  $run-main/disp8
    # . run-tests()
    e8/call  run-tests/disp32
    8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           3/r32/EBX   Num-test-failures/disp32          # copy *Num-test-failures to EBX
    eb/jump  $main:end/disp8
$run-main:
    # - otherwise read a program from stdin and emit its translation to stdout
    # var ed/EAX : exit-descriptor
    81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # subtract from ESP
    89/copy                         3/mod/direct    0/rm32/EAX    .           .             .           4/r32/ESP   .               .                 # copy ESP to EAX
    # configure ed to really exit()
    # . ed->target = 0
    c7          0/subop/copy        0/mod/direct    0/rm32/EAX    .           .             .           .           .               0/imm32           # copy to *EAX
    # return compile(Stdin, 1/stdout, 2/stderr, ed)
    # . . push args
    50/push-EAX/ed
    68/push  2/imm32/stderr
    68/push  1/imm32/stdout
    68/push  Stdin/imm32
    # . . call
    e8/call  compile/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0x10/imm32        # add to ESP
    # . syscall(exit, 0)
    bb/copy-to-EBX  0/imm32
$main:end:
    b8/copy-to-EAX  1/imm32/exit
    cd/syscall  0x80/imm8

# the main entry point
compile:  # in : (address buffered-file), out : fd or (address stream), err : fd or (address stream), ed : (address exit-descriptor) -> <void>
    # . prolog
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # . save registers
    50/push-EAX
    51/push-ECX
    # prime the pump
    # . Look = get-char(in)
    # . . push args
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8      .                    # push *(EBP+8)
    # . . call
    e8/call  get-char/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # var num/ECX : (address stream) on the stack
    # Numbers can be 32 bits or 8 hex bytes long. One of them will be in 'Look', so we need space for 7 bytes.
    # Sizing the stream just right buys us overflow-handling for free inside 'get-num'.
    # Add 12 bytes for 'read', 'write' and 'length' fields, for a total of 19 bytes, or 0x13 in hex.
    # The stack pointer is no longer aligned, so dump_stack() can be misleading past this point.
    81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               0x13/imm32        # subtract from ESP
    89/copy                         3/mod/direct    1/rm32/ECX    .           .             .           4/r32/ESP   .               .                 # copy ESP to ECX
    # initialize the stream
    # . num->length = 7
    c7          0/subop/copy        1/mod/*+disp8   1/rm32/ECX    .           .             .           .           8/disp8         7/imm32           # copy to *(ECX+8)
    # . clear-stream(num)
    # . . push args
    51/push-ECX
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # read a digit from 'in' into 'num'
    # . get-num(in, num, err, ed)
    # . . push args
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x14/disp8      .                 # push *(EBP+20)
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x10/disp8      .                 # push *(EBP+16)
    51/push-ECX/num
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8      .                    # push *(EBP+8)
    # . . call
    e8/call  get-num/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0x10/imm32        # add to ESP
    # render 'num' into the following template on 'out':
    #   bb/copy-to-EBX  _num_
    #   b8/copy-to-EAX  1/imm32/exit
    #   cd/syscall  0x80/imm8
    #
    # . write(out, "bb/copy-to-EBX  ")
    # . . push args
    68/push  "bb/copy-to-EBX  "/imm32
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # . write-stream(out, num)
    # . . push args
    51/push-ECX/num
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
    # . . call
    e8/call  write-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # . write(out, Newline)
    # . . push args
    68/push  Newline/imm32
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # . write(out, "b8/copy-to-EAX  1/imm32/exit\n")
    # . . push args
    68/push  "b8/copy-to-EAX  1/imm32/exit\n"/imm32
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # . write(out, "cd/syscall  0x80/imm8\n")
    # . . push args
    68/push  "cd/syscall  0x80/imm8\n"/imm32
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
$compile:end:
    # . restore registers
    59/pop-to-ECX
    58/pop-to-EAX
    # . epilog
    89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    5d/pop-to-EBP
    c3/return

# Read a single digit into 'out'. Abort if there are none, or if there is no space in 'out'.
# Input comes from the global variable 'Look', and we leave the next byte from
# 'in' into it on exit.
get-num:  # in : (address buffered-file), out : (address stream), err : fd or (address stream), ed : (address exit-descriptor) -> <void>
    # pseudocode:
    #   if (!is-digit?(Look)) expected(ed, err, "integer")
    #   if out->write >= out->length
    #     write(err, "Error: too many digits in number\n")
    #     stop(ed, 1)
    #   out->data[out->write] = LSB(Look)
    #   ++out->write
    #   Look = get-char(in)
    #
    # registers:
    #   in: ESI
    #   out: EDI
    #   out->write: ECX (cached copy; need to keep in sync)
    #   out->length: EDX
    #   temporaries: EAX, EBX
    # We can't allocate Look to a register because it gets written implicitly in
    # get-char in each iteration of the loop. (Thereby demonstrating that it's
    # not the right interface for us. But we'll keep it just to follow Crenshaw.)
    #
    # . prolog
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # - if (is-digit?(Look)) expected(ed, err, "integer")
    # . EAX = is-digit?(Look)
    # . . push args
    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Look/disp32     .                 # push *Look
    # . . call
    e8/call  is-digit?/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # . if (EAX == 0)
    3d/compare-EAX-and  0/imm32
    75/jump-if-not-equal  $get-num:main/disp8
    # . expected(ed, err, "integer")
    # . . push args
    68/push  "integer"/imm32
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x10/disp8      .                 # push *(EBP+16)
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x14/disp8      .                 # push *(EBP+20)
    # . . call
    e8/call  expected/disp32  # never returns
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
$get-num:main:
    # - otherwise read a digit
    # . save registers
    50/push-EAX
    51/push-ECX
    52/push-EDX
    53/push-EBX
    56/push-ESI
    57/push-EDI
    # read necessary variables to registers
    # ESI = in
    8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .             .           6/r32/ESI   8/disp8         .                 # copy *(EBP+8) to ESI
    # EDI = out
    8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .             .           7/r32/EDI   0xc/disp8       .                 # copy *(EBP+12) to EDI
    # ECX = out->write
    8b/copy                         0/mod/indirect  7/rm32/EDI    .           .             .           1/r32/ECX   .               .                 # copy *EDI to ECX
    # EDX = out->length
    8b/copy                         1/mod/*+disp8   7/rm32/EDI    .           .             .           2/r32/EDX   8/disp8         .                 # copy *(EDI+8) to EDX
    # if (out->write >= out->length) error
    39/compare                      3/mod/direct    2/rm32/EDX    .           .             .           1/r32/ECX   .               .                 # compare EDX with ECX
    7d/jump-if-lesser  $get-num:stage2/disp8
    # . error(ed, err, msg)  # TODO: show full number
    # . . push args
    68/push  "get-num: too many digits in number"/imm32
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x10/disp8      .                 # push *(EBP+16)
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x14/disp8      .                 # push *(EBP+20)
    # . . call
    e8/call  error/disp32  # never returns
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
$get-num:stage2:
    # out->data[out->write] = LSB(Look)
    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    7/base/EDI  1/index/ECX   .           3/r32/EBX   0xc/disp8       .                 # copy EDI+ECX+12 to EBX
    8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/EAX   Look/disp32     .                 # copy *Look to EAX
    88/copy-byte                    0/mod/indirect  3/rm32/EBX    .           .             .           0/r32/AL    .               .                 # copy byte at AL to *EBX
    # ++out->write
    41/increment-ECX
    # Look = get-char(in)
    # . . push args
    56/push-ESI
    # . . call
    e8/call  get-char/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
$get-num:loop-end:
    # persist necessary variables from registers
    89/copy                         0/mod/indirect  7/rm32/EDI    .           .             .           1/r32/ECX   .               .                 # copy ECX to *EDI
$get-num:end:
    # . restore registers
    5f/pop-to-EDI
    5e/pop-to-ESI
    5b/pop-to-EBX
    5a/pop-to-EDX
    59/pop-to-ECX
    58/pop-to-EAX
    # . epilog
    89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    5d/pop-to-EBP
    c3/return

test-get-num-reads-single-digit:
    # - check that get-num returns first character if it's a digit
    # This test uses exit-descriptors. Use EBP for setting up local variables.
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # clear all streams
    # . clear-stream(_test-stream)
    # . . push args
    68/push  _test-stream/imm32
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # . clear-stream(_test-buffered-file+4)
    # . . push args
    b8/copy-to-EAX  _test-buffered-file/imm32
    05/add-to-EAX  4/imm32
    50/push-EAX
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # . clear-stream(_test-output-stream)
    # . . push args
    68/push  _test-output-stream/imm32
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # . clear-stream(_test-error-stream)
    # . . push args
    68/push  _test-error-stream/imm32
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # initialize 'in'
    # . write(_test-stream, "3")
    # . . push args
    68/push  "3"/imm32
    68/push  _test-stream/imm32
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # initialize exit-descriptor 'ed' for the call to 'get-num' below
    # . var ed/EAX : exit-descriptor
    81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # subtract from ESP
    89/copy                         3/mod/direct    0/rm32/EAX    .           .             .           4/r32/ESP   .               .                 # copy ESP to EAX
    # . tailor-exit-descriptor(ed, 16)
    # . . push args
    68/push  0x10/imm32/nbytes-of-args-for-get-num
    50/push-EAX/ed
    # . . call
    e8/call  tailor-exit-descriptor/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # prime the pump
    # . get-char(_test-buffered-file)
    # . . push args
    68/push  _test-buffered-file/imm32
    # . . call
    e8/call  get-char/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # get-num(in, out, err, ed)
    # . . push args
    50/push-EAX/ed
    68/push  _test-error-stream/imm32
    68/push  _test-output-stream/imm32
    68/push  _test-buffered-file/imm32
    # . . call
    e8/call  get-num/disp32
    # registers except ESP may be clobbered at this point
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0x10/imm32        # add to ESP
    # check-ints-equal(*_test-output-stream->data, '3', msg)
    # . . push args
    68/push  "F - test-get-num-reads-single-digit"/imm32
    68/push  0x33/imm32
    b8/copy-to-EAX  _test-output-stream/imm32
    ff          6/subop/push        1/mod/*+disp8   0/rm32/EAX    .           .             .           .           0xc/disp8       .                 # push *(EAX+12)
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
    # . reclaim locals
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    5d/pop-to-EBP
    c3/return

test-get-num-aborts-on-non-digit-in-Look:
    # - check that get-num returns first character if it's a digit
    # This test uses exit-descriptors. Use EBP for setting up local variables.
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # clear all streams
    # . clear-stream(_test-stream)
    # . . push args
    68/push  _test-stream/imm32
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # . clear-stream(_test-buffered-file+4)
    # . . push args
    b8/copy-to-EAX  _test-buffered-file/imm32
    05/add-to-EAX  4/imm32
    50/push-EAX
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # . clear-stream(_test-output-stream)
    # . . push args
    68/push  _test-output-stream/imm32
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # . clear-stream(_test-error-stream)
    # . . push args
    68/push  _test-error-stream/imm32
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # initialize 'in'
    # . write(_test-stream, "3")
    # . . push args
    68/push  "3"/imm32
    68/push  _test-stream/imm32
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # initialize exit-descriptor 'ed' for the call to 'get-num' below
    # . var ed/EAX : (address exit-descriptor)
    81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # subtract from ESP
    89/copy                         3/mod/direct    0/rm32/EAX    .           .             .           4/r32/ESP   .               .                 # copy ESP to EAX
    # . tailor-exit-descriptor(ed, 16)
    # . . push args
    68/push  0x10/imm32/nbytes-of-args-for-get-num
    50/push-EAX/ed
    # . . call
    e8/call  tailor-exit-descriptor/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # *don't* prime the pump
    # get-num(in, out, err, ed)
    # . . push args
    50/push-EAX/ed
    68/push  _test-error-stream/imm32
    68/push  _test-output-stream/imm32
    68/push  _test-buffered-file/imm32
    # . . call
    e8/call  get-num/disp32
    # registers except ESP may be clobbered at this point
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0x10/imm32        # add to ESP
    # check that get-num tried to call exit(1)
    # . check-ints-equal(ed->value, 2, msg)  # i.e. stop was called with value 1
    # . . push args
    68/push  "F - test-get-num-aborts-on-non-digit-in-Look"/imm32
    68/push  2/imm32
    # . . push ed->value
    ff          6/subop/push        1/mod/*+disp8   0/rm32/EAX    .           .             .           .           4/disp8         .                 # push *(EAX+4)
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
    # . reclaim locals
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    5d/pop-to-EBP
    c3/return

## helpers

# write(f, "Error: "+s+" expected\n") then stop(ed, 1)
expected:  # ed : (address exit-descriptor), f : fd or (address stream), s : (address array byte) -> <void>
    # . prolog
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # write(f, "Error: ")
    # . . push args
    68/push  "Error: "/imm32
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # write(f, s)
    # . . push args
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x10/disp8      .                 # push *(EBP+16)
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # write(f, " expected")
    # . . push args
    68/push  " expected\n"/imm32
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # stop(ed, 1)
    # . . push args
    68/push  1/imm32
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         .                 # push *(EBP+8)
    # . . call
    e8/call  stop/disp32
    # should never get past this point
$expected:dead-end:
    # . epilog
    89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    5d/pop-to-EBP
    c3/return

# read a byte from 'f', and save it in 'Look'
get-char:  # f : (address buffered-file) -> <void>
    # . prolog
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # . save registers
    50/push-EAX
    # EAX = read-byte-buffered(f)
    # . . push args
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         .                 # push *(EBP+8)
    # . . call
    e8/call  read-byte-buffered/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # save EAX to Look
    89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/EAX   Look/disp32     .                 # copy EAX to *Look
$get-char:end:
    # . restore registers
    58/pop-to-EAX
    # . epilog
    89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    5d/pop-to-EBP
    c3/return

is-digit?:  # c : int -> EAX : boolean
    # . prolog
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # EAX = false
    b8/copy-to-EAX  0/imm32
    # if (c < '0') return false
    81          7/subop/compare     1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         0x30/imm32        # compare *(EBP+8)
    7c/jump-if-lesser  $is-digit?:end/disp8
    # if (c > '9') return false
    81          7/subop/compare     1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         0x39/imm32        # compare *(EBP+8)
    7f/jump-if-greater  $is-digit?:end/disp8
    # otherwise return true
    b8/copy-to-EAX  1/imm32
$is-digit?:end:
    # . epilog
    89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    5d/pop-to-EBP
    c3/return

== data

Look:  # (char with some extra padding)
    0/imm32

_test-output-stream:
    # current write index
    0/imm32
    # current read index
    0/imm32
    # length
    8/imm32
    # data
    00 00 00 00 00 00 00 00  # 8 bytes

_test-error-stream:
    # current write index
    0/imm32
    # current read index
    0/imm32
    # length
    0x40/imm32
    # data (4 lines x 16 bytes/line)
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

# . . vim:nowrap:textwidth=0