## 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
  # syscall(exit, 0)
  bb/copy-to-EBX  0/imm32
  b8/copy-to-EAX  1/imm32/exit
  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
  # syscall(exit, 1)
  bb/copy-to-EBX  1/imm32
  b8/copy-to-EAX  1/imm32/exit
  cd/syscall  0x80/imm8

# print out "Error: #{s} expected\n" to stderr
error:  # s : (address array byte) -> <void>
  # _write(2/stderr, "Error: ")
    # push args
  68/push  "Error: "/imm32
  68/push  2/imm32/stderr
    # call
  e8/call  _write/disp32
    # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
  # _write(2/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)
  68/push  2/imm32/stderr
    # call
  e8/call  _write/disp32
    # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
  # _write(2/stderr, " expected")
    # push args
  68/push  " expected"/imm32
  68/push  2/imm32/stderr
    # call
  e8/call  _write/disp32
    # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
  # _write(2/stderr, "\n")
    # push args
  68/push  Newline/imm32
  68/push  2/imm32/stderr
    # call
  e8/call  _write/disp32
    # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
  # end
  c3/return

# vim:nowrap:textwidth=0