## port of https://github.com/akkartik/crenshaw/blob/master/tutor2.1.pas
# corresponds to the section "single digits" in https://compilers.iecc.com/crenshaw/tutor2.txt
#
# To run (from the subx directory):
#   $ subx translate *.subx apps/crenshaw2.1.subx -o crenshaw 2.1
#   $ echo '3'  |subx run apps/crenshaw2.1  |xxd -
# Expected output:
#   TODO
#
# The output is the code a function would need to include, returning the
# result in EAX.
#
# Major note: byte strings are not null-terminated. Instead they're prefixed
# with a 32-bit length.

== code
# instruction                     effective address                                                   operand     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

# main:
  # abort("Integer")
    # push args
  68/push  "Integer"/imm32
    # call
  e8/call  abort/disp32
    # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
  # exit(0)
  bb/copy                         .               .             .           .             .           .           .               0/imm32           # copy to EBX
  b8/copy                         .               .             .           .             .           .           .               1/imm32/exit      # copy to EAX
  cd/syscall  0x80/imm8

## helpers

# print error message and exit
# really maps to the 'Expected' function in Crenshaw
abort:  # s : (address array byte) -> <void>
  # error(s)
    # push args
  ff          6/subop/push        1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none  .           .           4/disp8         .                 # push *(ESP+4)
    # call
  e8/call  error/disp32
    # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
  # exit(1)
  bb/copy                         .               .             .           .             .           .           .               1/imm32           # copy to EBX
  b8/copy                         .               .             .           .             .           .           .               1/imm32/exit      # copy to EAX
  cd/syscall  0x80/imm8

# print out "Error: #{s} expected\n" to stderr
error:  # s : (address array byte) -> <void>
  # write_stderr("Error: ")
    # push args
  68/push  "Error: "/imm32
    # call
  e8/call  write_stderr/disp32
    # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
  # write_stderr(s)
    # push args
  ff          6/subop/push        1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none  .           .           4/disp8         .                 # push *(ESP+4)
    # call
  e8/call  write_stderr/disp32
    # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
  # write_stderr(" expected")
    # push args
  68/push  " expected"/imm32
    # call
  e8/call  write_stderr/disp32
    # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
  # write_stderr("\n")
    # push args
  68/push  Newline/imm32
    # call
  e8/call  write_stderr/disp32
    # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
  # end
  c3/return

write_stdout:  # s : (address array byte) -> <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
  52/push-EDX
  53/push-EBX
  # write(1/stdout, (data) s+4, (size) *s)
    # fd = 1 (stdout)
  bb/copy                         .               .             .           .             .           .           .               1/imm32           # copy to EBX
    # x = s+4
  8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           1/r32/ECX   8/disp8         .                 # copy *(EBP+8) to ECX
  81          0/subop/add         3/mod/direct    1/rm32/ECX    .           .             .           .           .               4/imm32           # add to ECX
    # size = *s
  8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           2/r32/EDX   8/disp8         .                 # copy *(EBP+8) to EDX
  8b/copy                         0/mod/indirect  2/rm32/EDX    .           .             .           2/r32/EDX   .               .                 # copy *EDX to EDX
    # call write()
  b8/copy                         .               .             .           .             .           .           .               4/imm32/write     # copy to EAX
  cd/syscall  0x80/imm8
  # restore registers
  5b/pop-to-EBX
  5a/pop-to-EDX
  59/pop-to-ECX
  58/pop-to-EAX
  # end
  89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
  5d/pop-to-EBP
  c3/return

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