src/gifs/lainchan/tohya.png

# write-byte-buffered: add a single byte to a buffered-file.
# flush: write out any buffered writes to disk.
#
# TODO: Come up with a way to signal failure to write to disk. This is hard
# since the failure may impact previous calls that were buffered.

== data

# The buffered file for standard output.
Stdout:
    # file descriptor or (address stream)
    1/imm32  # standard output
Stdout->buffer:
    # inlined fields for a 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

# TODO: 8 bytes is too small. We'll need to grow the buffer for efficiency. But
# I don't want to type in 1024 bytes here.

== 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

# Write lower byte of 'n' to 'f'.
write-byte-buffered:  # f : (address buffered-file), n : int
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # . save registers
    51/push-ecx
    57/push-edi
    # edi = f
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           7/r32/edi   8/disp8         .                 # copy *(ebp+8) to edi
    # ecx = f->write
    8b/copy                         1/mod/*+disp8   7/rm32/edi    .           .             .           1/r32/ecx   4/disp8         .                 # copy *(edi+4) to ecx
    # if (f->write >= f->length) flush and clear f's stream
    3b/compare                      1/mod/*+disp8   7/rm32/edi    .           .             .           1/r32/ecx   0xc/disp8       .                 # compare ecx with *(edi+12)
    7c/jump-if-lesser  $write-byte-buffered:to-stream/disp8
    # . flush(f)
    # . . push args
    57/push-edi
    # . . call
    e8/call  flush/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # . clear-stream(stream = f+4)
    # . . push args
    8d/copy-address                 1/mod/*+disp8   7/rm32/edi    .           .             .           0/r32/eax   4/disp8         .                 # copy edi+4 to eax
    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
    # . f->write must now be 0; update its cache at ecx
    31/xor                          3/mod/direct    1/rm32/ecx    .           .             .           1/r32/ecx   .               .                 # clear ecx
$write-byte-buffered:to-stream:
    # write to stream
    # f->data[f->write] = LSB(n)
    31/xor                          3/mod/direct    0/rm32/eax    .           .             .           0/r32/eax   .               .                 # clear eax
    8a/copy-byte                    1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/AL    0xc/disp8       .                 # copy byte at *(ebp+12) to AL
    88/copy-byte                    1/mod/*+disp8   4/rm32/sib    7/base/edi  1/index/ecx   .           0/r32/AL    0x10/disp8      .                 # copy AL to *(edi+ecx+16)
    # ++f->write
    ff          0/subop/increment   1/mod/*+disp8   7/rm32/edi    .           .             .           .           4/disp8         .                 # increment *(edi+4)
$write-byte-buffered:end:
    # . restore registers
    5f/pop-to-edi
    59/pop-to-ecx
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

flush:  # f : (address buffered-file)
    # . prologue
    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
    # eax = f
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/eax   8/disp8         .                 # copy *(ebp+8) to eax
    # write-stream(f->fd, data = f+4)
      # . . push args
    8d/copy-address                 1/mod/*+disp8   0/rm32/eax    .           .             .           1/r32/ecx   4/disp8         .                 # copy eax+4 to ecx
    51/push-ecx
    ff          6/subop/push        0/mod/indirect  0/rm32/eax    .           .             .           .           .               .                 # push *eax
      # . . call
    e8/call  write-stream/disp32
      # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
$flush:end:
    # . restore registers
    59/pop-to-ecx
    58/pop-to-eax
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

test-write-byte-buffered-single:
    # - check that write-byte-buffered writes to first byte of 'file'
    # setup
    # . 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->buffer)
    # . . push args
    68/push  _test-buffered-file->buffer/imm32
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # write-byte-buffered(_test-buffered-file, 'A')
    # . . push args
    68/push  0x41/imm32
    68/push  _test-buffered-file/imm32
    # . . call
    e8/call  write-byte-buffered/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # flush(_test-buffered-file)
    # . . push args
    68/push  _test-buffered-file/imm32
    # . . call
    e8/call  flush/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # check-stream-equal(_test-stream, "A", msg)
    # . . push args
    68/push  "F - test-write-byte-buffered-single"/imm32
    68/push  "A"/imm32
    68/push  _test-stream/imm32
    # . . call
    e8/call  check-stream-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # . end
    c3/return

test-write-byte-buffered-multiple-flushes:
    # - check that write-byte-buffered correctly flushes buffered data
    # setup
    # . 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->buffer)
    # . . push args
    68/push  _test-buffered-file->buffer/imm32
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # fill up the buffer for _test-buffered-file
    # . write(_test-buffered-file->buffer, "abcdef")
    # . . push args
    68/push  "abcdef"/imm32
    68/push  _test-buffered-file->buffer/imm32
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # write-byte-buffered(_test-buffered-file, 'g')
    # . . push args
    68/push  0x67/imm32
    68/push  _test-buffered-file/imm32
    # . . call
    e8/call  write-byte-buffered/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # flush(_test-buffered-file)
    # . . push args
    68/push  _test-buffered-file/imm32
    # . . call
    e8/call  flush/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # check-stream-equal(_test-stream, "abcdefg", msg)
    # . . push args
    68/push  "F - test-write-byte-buffered-multiple-flushes"/imm32
    68/push  "abcdefg"/imm32
    68/push  _test-stream/imm32
    # . . call
    e8/call  check-stream-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # . end
    c3/return

# - variant without buffering

# Write lower byte of 'n' to 'f'.
append-byte:  # f : (address stream), n : int
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # . save registers
    51/push-ecx
    57/push-edi
    # edi = f
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           7/r32/edi   8/disp8         .                 # copy *(ebp+8) to edi
    # ecx = f->write
    8b/copy                         0/mod/indirect  7/rm32/edi    .           .             .           1/r32/ecx   .               .                 # copy *edi to ecx
    # if (f->write >= f->length) abort
    3b/compare                      1/mod/*+disp8   7/rm32/edi    .           .             .           1/r32/ecx   8/disp8         .                 # compare ecx with *(edi+8)
    7d/jump-if-greater-or-equal  $append-byte:abort/disp8
$append-byte:to-stream:
    # write to stream
    # f->data[f->write] = LSB(n)
    31/xor                          3/mod/direct    0/rm32/eax    .           .             .           0/r32/eax   .               .                 # clear eax
    8a/copy-byte                    1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/AL    0xc/disp8       .                 # copy byte at *(ebp+12) to AL
    88/copy-byte                    1/mod/*+disp8   4/rm32/sib    7/base/edi  1/index/ecx   .           0/r32/AL    0xc/disp8       .                 # copy AL to *(edi+ecx+12)
    # ++f->write
    ff          0/subop/increment   0/mod/indirect  7/rm32/edi    .           .             .           .           .               .                 # increment *edi
$append-byte:end:
    # . restore registers
    5f/pop-to-edi
    59/pop-to-ecx
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

$append-byte:abort:
    # . _write(2/stderr, error)
    # . . push args
    68/push  "append-byte: out of space\n"/imm32
    68/push  2/imm32/stderr
    # . . call
    e8/call  _write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # . syscall(exit, 1)
    bb/copy-to-ebx  1/imm32
    b8/copy-to-eax  1/imm32/exit
    cd/syscall  0x80/imm8
    # never gets here

test-append-byte-single:
    # - check that append-byte writes to first byte of 'file'
    # setup
    # . 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
    # append-byte(_test-stream, 'A')
    # . . push args
    68/push  0x41/imm32
    68/push  _test-stream/imm32
    # . . call
    e8/call  append-byte/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # check-stream-equal(_test-stream, "A", msg)
    # . . push args
    68/push  "F - test-append-byte-single"/imm32
    68/push  "A"/imm32
    68/push  _test-stream/imm32
    # . . call
    e8/call  check-stream-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # . end
    c3/return

== data

_test-output-stream:
    # current write index
    0/imm32
    # current read index
    0/imm32
    # length
    0x200/imm32  # 512 bytes
    # data (32 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
    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
    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
    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
    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
    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
    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
    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

# a test buffered file for _test-output-stream
_test-output-buffered-file:
    # file descriptor or (address stream)
    _test-output-stream/imm32
_test-output-buffered-file->buffer:
    # current write index
    0/imm32
    # current read index
    0/imm32
    # length
    6/imm32
    # data
    00 00 00 00 00 00  # 6 bytes

_test-error-stream:
    # current write index
    0/imm32
    # current read index
    0/imm32
    # line
    0x80/imm32  # 128 bytes
    # data (8 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
    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

# a test buffered file for _test-error-stream
_test-error-buffered-file:
    # file descriptor or (address stream)
    _test-error-stream/imm32
_test-error-buffered-file->buffer:
    # current write index
    0/imm32
    # current read index
    0/imm32
    # length
    6/imm32
    # data
    00 00 00 00 00 00  # 6 bytes

# . . vim:nowrap:textwidth=0