# Helper to allocate a stream on the heap.

== 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

new-stream:  # ad : (addr allocation-descriptor), length : int, elemsize : int -> address/eax : (handle stream _)
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # . save registers
    52/push-edx
    # var n/eax : int = elemsize * length + 12 (for read, write and length)
    # . eax = elemsize
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/eax   0x10/disp8      .                 # copy *(ebp+16) to eax
    # . eax *= length
    31/xor                          3/mod/direct    2/rm32/edx    .           .             .           2/r32/edx   .               .                 # clear edx
    f7          4/subop/multiply    1/mod/*+disp8   5/rm32/ebp    .           .                                     0xc/disp8       .                 # multiply *(ebp+12) into eax
    # . if overflow abort
    81          7/subop/compare     3/mod/direct    2/rm32/edx    .           .             .           .           .               0/imm32           # compare edx
    75/jump-if-not-equal  $new-stream:abort/disp8
    # . edx = elemsize*length
    89/copy                         3/mod/direct    2/rm32/edx    .           .             .           0/r32/eax   .               .                 # copy eax to edx
    # . eax += 12
    05/add-to-eax  0xc/imm32
    # var eax : (handle stream _) = allocate(ad, n)
    # . . push args
    50/push-eax
    ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         .                 # push *(ebp+8)
    # . . call
    e8/call  allocate/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # eax->length = elemsize*length
    89/copy                         1/mod/*+disp8   0/rm32/eax    .           .             .           2/r32/edx   8/disp8         .                 # copy edx to *(eax+8)
    # clear-stream(eax)
    # . . push args
    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
$new-stream:end:
    # . restore registers
    5a/pop-to-edx
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

$new-stream:abort:
    # . _write(2/stderr, error)
    # . . push args
    68/push  "new-stream: size too large\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-new-stream:
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # var heap/ecx : (ref allocation-descriptor)
    68/push  0/imm32/limit
    68/push  0/imm32/curr
    89/copy                         3/mod/direct    1/rm32/ecx    .           .             .           4/r32/esp   .               .                 # copy esp to ecx
    # heap = new-segment(512)
    # . . push args
    51/push-ecx
    68/push  0x200/imm32
    # . . call
    e8/call  new-segment/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # var start/edx = ad->curr
    8b/copy                         0/mod/indirect  1/rm32/ecx    .           .             .           2/r32/edx   .               .                 # copy *ecx to edx
    # var eax : (handle stream byte) = new-stream(heap, 3, 2)
    # . . push args
    68/push  2/imm32
    68/push  3/imm32
    51/push-ecx
    # . . call
    e8/call  new-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # check-ints-equal(eax, edx, msg)
    # . . push args
    68/push  "F - test-new-stream: returns current pointer of allocation descriptor"/imm32
    52/push-edx
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # check-ints-equal(eax->length, 6, msg)
    # . . push args
    68/push  "F - test-new-stream: sets length correctly"/imm32
    68/push  6/imm32
    ff          6/subop/push        1/mod/*+disp8   0/rm32/eax    .           .             .           .           .               8/disp8           # push *(eax+8)
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # the rest is delegated to clear-stream() so we won't bother checking it
    # . epilogue
    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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