# Helpers to compute widths of SubX arguments based on their metadata.
#   /imm8 => 1 byte,
#   /disp32 => 4 bytes,
#   and so on.

== 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

compute-width:  # word: (addr array byte) -> result/eax: 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
    # eax = word
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/eax   8/disp8         .                 # copy *(ebp+8) to ecx
    # var ecx: (addr byte) = &word[word->size]
    8b/copy                         0/mod/indirect  0/rm32/eax    .           .             .           1/r32/ecx   .               .                 # copy *eax to ecx
    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    0/base/eax  1/index/ecx   .           1/r32/ecx   4/disp8         .                 # copy eax+ecx+4 to ecx
    # eax = word->data
    05/add-to-eax  4/imm32
    # var in/ecx: slice = {eax, ecx}
    51/push-ecx
    50/push-eax
    89/copy                         3/mod/direct    1/rm32/ecx    .           .             .           4/r32/esp   .               .                 # copy esp to ecx
    # return compute-width-of-slice(ecx)
    # . . push args
    51/push-ecx
    # . . call
    e8/call  compute-width-of-slice/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
$compute-width:end:
    # . reclaim locals
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # . restore registers
    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

compute-width-of-slice:  # s: (addr slice) -> result/eax: 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
    # ecx = s
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           1/r32/ecx   8/disp8         .                 # copy *(ebp+8) to ecx
    # if (has-metadata?(word, "imm32")) return 4
    # . eax = has-metadata?(word, "imm32")
    # . . push args
    68/push  "imm32"/imm32
    51/push-ecx
    # . . call
    e8/call  has-metadata?/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # . if (eax != false) return 4
    3d/compare-eax-and  0/imm32/false
    b8/copy-to-eax  4/imm32         # ZF is set, so we can overwrite eax now
    75/jump-if-!=  $compute-width-of-slice:end/disp8
    # if (has-metadata?(word, "disp32")) return 4
    # . eax = has-metadata?(word, "disp32")
    # . . push args
    68/push  "disp32"/imm32
    51/push-ecx
    # . . call
    e8/call  has-metadata?/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # . if (eax != false) return 4
    3d/compare-eax-and  0/imm32/false
    b8/copy-to-eax  4/imm32         # ZF is set, so we can overwrite eax now
    75/jump-if-!=  $compute-width-of-slice:end/disp8
    # if (has-metadata?(word, "imm16")) return 2
    # . eax = has-metadata?(word, "imm16")
    # . . push args
    68/push  "imm16"/imm32
    51/push-ecx
    # . . call
    e8/call  has-metadata?/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # . if (eax != false) return 2
    3d/compare-eax-and  0/imm32/false
    b8/copy-to-eax  2/imm32         # ZF is set, so we can overwrite eax now
    75/jump-if-!=  $compute-width-of-slice:end/disp8
    # if (has-metadata?(word, "disp16")) return 2
    # . eax = has-metadata?(word, "disp16")
    # . . push args
    68/push  "disp16"/imm32
    51/push-ecx
    # . . call
    e8/call  has-metadata?/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # . if (eax != false) return 2
    3d/compare-eax-and  0/imm32/false
    b8/copy-to-eax  2/imm32         # ZF is set, so we can overwrite eax now
    75/jump-if-!=  $compute-width-of-slice:end/disp8
    # otherwise return 1
    b8/copy-to-eax  1/imm32
$compute-width-of-slice:end:
    # . restore registers
    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

test-compute-width:
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
$test-compute-width:imm8:
    # eax = compute-width("0x2/imm8")
    # . . push args
    68/push  "0x2/imm8"/imm32
    # . . call
    e8/call  compute-width/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # check-ints-equal(eax, 1, msg)
    # . . push args
    68/push  "F - test-compute-width: 0x2/imm8"/imm32
    50/push-eax
    68/push  1/imm32
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
$test-compute-width:imm16:
    # eax = compute-width("4/imm16")
    # . . push args
    68/push  "4/imm16"/imm32
    # . . call
    e8/call  compute-width/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # check-ints-equal(eax, 2, msg)
    # . . push args
    68/push  "F - test-compute-width: 4/imm16"/imm32
    50/push-eax
    68/push  2/imm32
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
$test-compute-width:imm32:
    # eax = compute-width("4/imm32")
    # . . push args
    68/push  "4/imm32"/imm32
    # . . call
    e8/call  compute-width/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # check-ints-equal(eax, 4, msg)
    # . . push args
    68/push  "F - test-compute-width: 4/imm32"/imm32
    50/push-eax
    68/push  4/imm32
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
$test-compute-width:disp8:
    # eax = compute-width("foo/disp8")
    # . . push args
    68/push  "foo/disp8"/imm32
    # . . call
    e8/call  compute-width/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # check-ints-equal(eax, 1, msg)
    # . . push args
    68/push  "F - test-compute-width: foo/disp8"/imm32
    50/push-eax
    68/push  1/imm32
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
$test-compute-width:disp16:
    # eax = compute-width("foo/disp16")
    # . . push args
    68/push  "foo/disp16"/imm32
    # . . call
    e8/call  compute-width/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # check-ints-equal(eax, 2, msg)
    # . . push args
    68/push  "F - test-compute-width: foo/disp16"/imm32
    50/push-eax
    68/push  2/imm32
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
$test-compute-width:disp32:
    # eax = compute-width("foo/disp32")
    # . . push args
    68/push  "foo/disp32"/imm32
    # . . call
    e8/call  compute-width/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # check-ints-equal(eax, 4, msg)
    # . . push args
    68/push  "F - test-compute-width: foo/disp32"/imm32
    50/push-eax
    68/push  4/imm32
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
$test-compute-width:no-metadata:
    # eax = compute-width("45")
    # . . push args
    68/push  "45"/imm32
    # . . call
    e8/call  compute-width/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # check-ints-equal(eax, 1, msg)
    # . . push args
    68/push  "F - test-compute-width: 45 (no metadata)"/imm32
    50/push-eax
    68/push  1/imm32
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # . 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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