# 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

# main:
    e8/call  run-tests/disp32  # 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'.
    # 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

new-stream:  # ad : (address allocation-descriptor), length : int, elemsize : int -> address/EAX
    # . prolog
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # . save registers
    52/push-EDX
    # n = 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
    # 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
    # . epilog
    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"/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:
    # . prolog
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # var ad/ECX : (address allocation-descriptor) = allocate-region(Heap, 512)
    # . EAX = allocate-region(Heap, 512)
    # . . push args
    68/push  0x200/imm32
    68/push  Heap/imm32
    # . . call
    e8/call  allocate-region/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # . ECX = EAX
    89/copy                         3/mod/direct    1/rm32/ECX    .           .             .           0/r32/EAX   .               .                 # copy EAX to ECX
    # var start/EDX = ad->curr
    8b/copy                         0/mod/indirect  1/rm32/ECX    .           .             .           2/r32/EDX   .               .                 # copy *ECX to EDX
    # EAX = new-stream(ad, 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
    # . epilog
    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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