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== 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 a single test, while debugging
#?     e8/call test-read-line/disp32
#?     # syscall(exit, Num-test-failures)
#?     8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           3/r32/EBX   Num-test-failures/disp32          # copy *Num-test-failures to EBX
#?     b8/copy-to-EAX  1/imm32/exit
#?     cd/syscall  0x80/imm8

# read bytes from 'f' until (and including) a newline and store them into 's'
# 's' fails to grow if and only if no data found
# just abort if 's' is too small
read-line:  # f : (address buffered-file), s : (address stream byte) -> <void>
    # pseudocode:
    #   while true
    #     if (s->write >= s->length) abort
    #     if (f->read >= f->write) populate stream from file
    #     if (f->write == 0) break
    #     AL = f->data[f->read]
    #     s->data[s->write] = AL
    #     ++f->read
    #     ++s->write
    #     if (AL == '\n') break
    # . 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
    56/push-ESI
    57/push-EDI
    # ESI = f
    8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .             .           6/r32/ESI   8/disp8         .                 # copy *(EBP+8) to ESI
    # ECX = f->read
    8b/copy                         1/mod/*+disp8   6/rm32/ESI    .           .             .           1/r32/ECX   8/disp8         .                 # copy *(ESI+8) to ECX
    # EDI = s
    8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .             .           7/r32/EDI   0xc/disp8       .                 # copy *(EBP+12) to EDI
    # EDX = s->write
    8b/copy                         0/mod/indirect  7/rm32/EDI    .           .             .           2/r32/EDX   .               .                 # copy *EDI to EDX
$read-line:loop:
    # if (s->write >= s->length) abort
    3b/compare                      1/mod/*+disp8   7/rm32/EDI    .           .             .           2/r32/EDX   8/disp8         .                 # compare EDX with *(EDI+8)
    7d/jump-if-greater-or-equal  $read-line:abort/disp8
    # if (f->read >= f->write) populate stream from file
    3b/compare                      1/mod/*+disp8   6/rm32/ESI    .           .             .           1/r32/ECX   4/disp8         .                 # compare ECX with *(ESI+4)
    7c/jump-if-lesser  $read-line:from-stream/disp8
    # . clear-stream(stream = f+4)
    # . . push args
    8d/copy-address                 1/mod/*+disp8   6/rm32/ESI    .           .             .           0/r32/EAX   4/disp8         .                 # copy ESI+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->read must now be 0; update its cache at ECX
    31/xor                          3/mod/direct    1/rm32/ECX    .           .             .           1/r32/ECX   .               .                 # clear ECX
    # . EAX = read(f->fd, stream = f+4)
    # . . push args
    50/push-EAX
    ff          6/subop/push        0/mod/indirect  6/rm32/ESI    .           .             .           .           .               .                 # push *ESI
    # . . call
    e8/call  read/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # if (f->write == 0) break
    # since f->read was initially 0, EAX is the same as f->write
    # . if (EAX == 0) return true
    3d/compare-EAX-and  0/imm32
    74/jump-if-equal  $read-line:end/disp8
$read-line:from-stream:
    # AL = f->data[f->read]
    31/xor                          3/mod/direct    0/rm32/EAX    .           .             .           0/r32/EAX   .               .                 # clear EAX
    8a/copy-byte                    1/mod/*+disp8   4/rm32/sib    6/base/ESI  1/index/ECX   .           0/r32/AL    0x10/disp8      .                 # copy byte at *(ESI+ECX+16) to AL
    # s->data[s->write] = AL
    88/copy-byte                    1/mod/*+disp8   4/rm32/sib    7/base/EDI  2/index/EDX   .           0/r32/AL    0xc/disp8       .                 # copy AL to *(EDI+EDX+12)
    # ++f->read
    41/increment-ECX
    # ++s->write
    42/increment-EDX
    # if (AL == '\n') return
    3d/compare-EAX-and  0xa/imm32
    75/jump-if-not-equal  $read-line:loop/disp8
$read-line:end:
    # save f->read
    89/copy                         1/mod/*+disp8   6/rm32/ESI    .           .             .           1/r32/ECX   8/disp8         .                 # copy ECX to *(ESI+8)
    # save s->write
    89/copy                         0/mod/indirect  7/rm32/EDI    .           .             .           2/r32/EDX   .               .                 # copy EDX to *EDI
    # . restore registers
    5f/pop-to-EDI
    5e/pop-to-ESI
    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

$read-line:abort:
    # . _write(2/stderr, error)
    # . . push args
    68/push  "read-line: line too long\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-read-line:
    # - check that read-line stops at a newline
    # 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+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-tmp-stream)
    # . . push args
    68/push  _test-tmp-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(_test-stream, "ab\ncd")
    # . . push args
    68/push  "ab\ncd"/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
    # read a line from _test-stream (buffered by _test-buffered-file) into _test-tmp-stream
    # . EAX = read-line(_test-buffered-file, _test-tmp-stream)
    # . . push args
    68/push  _test-tmp-stream/imm32
    68/push  _test-buffered-file/imm32
    # . . call
    e8/call  read-line/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # check-next-stream-line-equal(_test-tmp-stream, "ab", msg)
    # . . push args
    68/push  "F - test-read-line"/imm32
    68/push  "ab"/imm32
    68/push  _test-tmp-stream/imm32
    # . . call
    e8/call  check-next-stream-line-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
    # end
    c3/return

test-read-line-reads-final-line-until-Eof:
    # 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+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-tmp-stream)
    # . . push args
    68/push  _test-tmp-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(_test-stream, "cd")
    # . . push args
    68/push  "cd"/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
    # read a line from _test-stream (buffered by _test-buffered-file) into _test-tmp-stream
    # . EAX = read-line(_test-buffered-file, _test-tmp-stream)
    # . . push args
    68/push  _test-tmp-stream/imm32
    68/push  _test-buffered-file/imm32
    # . . call
    e8/call  read-line/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # check-stream-equal(_test-tmp-stream, "cd", msg)
    # . . push args
    68/push  "F - test-read-line-reads-final-line-until-Eof"/imm32
    68/push  "cd"/imm32
    68/push  _test-tmp-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