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authorKartik Agaram <vc@akkartik.com>2020-01-19 23:38:06 -0800
committerKartik Agaram <vc@akkartik.com>2020-01-19 23:38:06 -0800
commit41e4cfc33f02cc924f867ad86321591d77891d4c (patch)
tree5502901f9d9784d8fecd17588dbdbd4b80b6455c /html/076next-word.subx.html
parent33258e0ad2b5bbae249ca0558bdeb463af7b6148 (diff)
downloadmu-41e4cfc33f02cc924f867ad86321591d77891d4c.tar.gz
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0 files changed, 0 insertions, 0 deletions
 

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# write-int: add (the binary representation of) a single int to a stream

== 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-int:  # out: (addr stream byte), n: int
    # . 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
    57/push-edi
    # edi = out
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           7/r32/edi   8/disp8         .                 # copy *(ebp+8) to edi
    # ecx = out->write
    8b/copy                         0/mod/indirect  7/rm32/edi    .           .             .           1/r32/ecx   .               .                 # copy *edi to ecx
    # if (out->write >= out->size) abort
    3b/compare                      1/mod/*+disp8   7/rm32/edi    .           .             .           1/r32/ecx   8/disp8         .                 # compare ecx with *(edi+8)
    7d/jump-if->=  $write-int:abort/disp8
$write-int:to-stream:
    # out->data[out->write] = n
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/eax   0xc/disp8       .                 # copy *(ebp+12) to eax
    89/copy                         1/mod/*+disp8   4/rm32/sib    7/base/edi  1/index/ecx   .           0/r32/eax   0xc/disp8       .                 # copy eax to *(edi+ecx+12)
    # out->write += 4
    81          0/subop/add         0/mod/indirect  7/rm32/edi    .           .             .           .           .               4/imm32           # add to *edi
$write-int:end:
    # . restore registers
    5f/pop-to-edi
    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

$write-int:abort:
    # . _write(2/stderr, error)
    # . . push args
    68/push  "write-int: 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
    e8/call  syscall_exit/disp32
    # never gets here

test-write-int-single:
    # - check that write-int writes to first int of 'stream'
    # 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
    # write-int(_test-stream, "abcd")
    # . . push args
    68/push  0x64636261/imm32
    68/push  _test-stream/imm32
    # . . call
    e8/call  write-int/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # check-stream-equal(_test-stream, "abcd", msg)
    # . . push args
    68/push  "F - test-write-int-single"/imm32
    68/push  "abcd"/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:
    # - check that write-int correctly appends multiple writes
    # 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
    # write-int(_test-stream, "abcd")
    # . . push args
    68/push  0x64636261/imm32
    68/push  _test-stream/imm32
    # . . call
    e8/call  write-int/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # write-int(_test-stream, "efgh")
    # . . push args
    68/push  0x68676665/imm32
    68/push  _test-stream/imm32
    # . . call
    e8/call  write-int/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # check-stream-equal(_test-stream, "abcdefgh", msg)
    # . . push args
    68/push  "F - test-write-byte-buffered-multiple"/imm32
    68/push  "abcdefgh"/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

# . . vim:nowrap:textwidth=0