https://github.com/akkartik/mu/blob/main/linux/126write-int-decimal.subx

      1 # Helper to print an int32 in decimal.
      2
      3 == code
      4 #   instruction                     effective address                                                   register    displacement    immediate
      5 # . op          subop               mod             rm32          base        index         scale       r32
      6 # . 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
      7
      8 write-int32-decimal:  # out: (addr stream byte), n: int
      9     # works by generating characters from lowest to highest and pushing them
     10     # to the stack, before popping them one by one into the stream
     11     #
     12     # pseudocode:
     13     #   push sentinel
     14     #   eax = abs(n)
     15     #   while true
     16     #     sign-extend eax into edx
     17     #     eax, edx = eax/10, eax%10
     18     #     edx += '0'
     19     #     push edx
     20     #     if (eax == 0) break
     21     #   if n < 0
     22     #     push '-'
     23     #   w = out->write
     24     #   curr = &out->data[out->write]
     25     #   max = &out->data[out->size]
     26     #   while true
     27     #     pop into eax
     28     #     if (eax == sentinel) break
     29     #     if (curr >= max) abort
     30     #     *curr = AL
     31     #     ++curr
     32     #     ++w
     33     #   out->write = w
     34     # (based on K&R itoa: https://en.wikibooks.org/wiki/C_Programming/stdlib.h/itoa)
     35     # (this pseudocode contains registers because operations like division
     36     # require specific registers in x86)
     37     #
     38     # . prologue
     39     55/push-ebp
     40     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
     41     # . save registers
     42     50/push-eax
     43     51/push-ecx
     44     52/push-edx
     45     53/push-ebx
     46     57/push-edi
     47     # const ten/ecx = 10
     48     b9/copy-to-ecx  0xa/imm32
     49     # push sentinel
     50     68/push  0/imm32/sentinel
     51     # var eax: int = abs(n)
     52     8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/eax   0xc/disp8       .                 # copy *(ebp+12) to eax
     53     3d/compare-eax-with  0/imm32
     54     7d/jump-if->=  $write-int32-decimal:read-loop/disp8
     55 $write-int32-decimal:negative:
     56     f7          3/subop/negate      3/mod/direct    0/rm32/eax    .           .             .           .           .               .                 # negate eax
     57 $write-int32-decimal:read-loop:
     58     # eax, edx = eax / 10, eax % 10
     59     99/sign-extend-eax-into-edx
     60     f7          7/subop/idiv        3/mod/direct    1/rm32/ecx    .           .             .           .           .               .                 # divide edx:eax by ecx, storing quotient in eax and remainder in edx
     61     # edx += '0'
     62     81          0/subop/add         3/mod/direct    2/rm32/edx    .           .             .           .           .               0x30/imm32        # add to edx
     63     # push edx
     64     52/push-edx
     65     # if (eax == 0) break
     66     3d/compare-eax-and  0/imm32
     67     7f/jump-if->  $write-int32-decimal:read-loop/disp8
     68 $write-int32-decimal:read-break:
     69     # if (n < 0) push('-')
     70     81          7/subop/compare     1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       0/imm32           # compare *(ebp+12)
     71     7d/jump-if->=  $write-int32-decimal:write/disp8
     72 $write-int32-decimal:push-negative:
     73     68/push  0x2d/imm32/-
     74 $write-int32-decimal:write:
     75     # edi = out
     76     8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           7/r32/edi   8/disp8         .                 # copy *(ebp+8) to edi
     77     # var w/edx: int = out->write
     78     8b/copy                         0/mod/indirect  7/rm32/edi    .           .             .           2/r32/edx   .               .                 # copy *edi to edx
     79     # var curr/ecx: (addr byte) = &out->data[out->write]
     80     8d/copy-address                 1/mod/*+disp8   4/rm32/sib    7/base/edi  2/index/edx   .           1/r32/ecx   0xc/disp8       .                 # copy ebx+edx+12 to ecx
     81     # var max/ebx: (addr byte) = &out->data[out->size]
     82     8b/copy                         1/mod/*+disp8   7/rm32/edi    .           .             .           3/r32/ebx   8/disp8         .                 # copy *(edi+8) to ebx
     83     8d/copy-address                 1/mod/*+disp8   4/rm32/sib    7/base/edi  3/index/ebx   .           3/r32/ebx   0xc/disp8       .                 # copy edi+ebx+12 to ebx
     84 $write-int32-decimal:write-loop:
     85     # pop into eax
     86     58/pop-to-eax
     87     # if (eax == sentinel) break
     88     3d/compare-eax-and  0/imm32/sentinel
     89     74/jump-if-=  $write-int32-decimal:write-break/disp8
     90     # if (curr >= max) abort
     91     39/compare                      3/mod/direct    1/rm32/ecx    .           .             .           3/r32/ebx   .               .                 # compare ecx with ebx
     92     73/jump-if-addr>=  $write-int32-decimal:abort/disp8
     93 $write-int32-decimal:write-char:
     94     # *curr = AL
     95     88/copy-byte                    0/mod/indirect  1/rm32/ecx    .           .             .           0/r32/AL    .               .                 # copy AL to byte at *ecx
     96     # ++curr
     97     41/increment-ecx
     98     # ++w
     99     42/increment-edx
    100     eb/jump  $write-int32-decimal:write-loop/disp8
    101 $write-int32-decimal:write-break:
    102     # out->write = w
    103     89/copy                         0/mod/indirect  7/rm32/edi    .           .             .           2/r32/edx   .               .                 # copy edx to *edi
    104 $write-int32-decimal:end:
    105     # . restore registers
    106     5f/pop-to-edi
    107     5b/pop-to-ebx
    108     5a/pop-to-edx
    109     59/pop-to-ecx
    110     58/pop-to-eax
    111     # . epilogue
    112     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    113     5d/pop-to-ebp
    114     c3/return
    115
    116 $write-int32-decimal:abort:
    117     # . _write(2/stderr, error)
    118     # . . push args
    119     68/push  "write-int32-decimal: out of space\n"/imm32
    120     68/push  2/imm32/stderr
    121     # . . call
    122     e8/call  _write/disp32
    123     # . . discard args
    124     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    125     # . syscall(exit, 1)
    126     bb/copy-to-ebx  1/imm32
    127     e8/call  syscall_exit/disp32
    128     # never gets here
    129
    130 test-write-int32-decimal:
    131     # - check that a single-digit number converts correctly
    132     # setup
    133     # . clear-stream(_test-stream)
    134     # . . push args
    135     68/push  _test-stream/imm32
    136     # . . call
    137     e8/call  clear-stream/disp32
    138     # . . discard args
    139     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    140     # write-int32-decimal(_test-stream, 9)
    141     # . . push args
    142     68/push  9/imm32
    143     68/push  _test-stream/imm32
    144     # . . call
    145     e8/call  write-int32-decimal/disp32
    146     # . . discard args
    147     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    148     # check-stream-equal(_test-stream, "9", msg)
    149     # . . push args
    150     68/push  "F - test-write-int32-decimal"/imm32
    151     68/push  "9"/imm32
    152     68/push  _test-stream/imm32
    153     # . . call
    154     e8/call  check-stream-equal/disp32
    155     # . . discard args
    156     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    157     # . end
    158     c3/return
    159
    160 test-write-int32-decimal-zero:
    161     # - check that 0 converts correctly
    162     # setup
    163     # . clear-stream(_test-stream)
    164     # . . push args
    165     68/push  _test-stream/imm32
    166     # . . call
    167     e8/call  clear-stream/disp32
    168     # . . discard args
    169     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    170     # write-int32-decimal(_test-stream, 0)
    171     # . . push args
    172     68/push  0/imm32
    173     68/push  _test-stream/imm32
    174     # . . call
    175     e8/call  write-int32-decimal/disp32
    176     # . . discard args
    177     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    178     # check-stream-equal(_test-stream, "0", msg)
    179     # . . push args
    180     68/push  "F - test-write-int32-decimal-zero"/imm32
    181     68/push  "0"/imm32
    182     68/push  _test-stream/imm32
    183     # . . call
    184     e8/call  check-stream-equal/disp32
    185     # . . discard args
    186     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    187     # . end
    188     c3/return
    189
    190 test-write-int32-decimal-multiple-digits:
    191     # - check that a multi-digit number converts correctly
    192     # setup
    193     # . clear-stream(_test-stream)
    194     # . . push args
    195     68/push  _test-stream/imm32
    196     # . . call
    197     e8/call  clear-stream/disp32
    198     # . . discard args
    199     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    200     # write-int32-decimal(_test-stream, 10)
    201     # . . push args
    202     68/push  0xa/imm32
    203     68/push  _test-stream/imm32
    204     # . . call
    205     e8/call  write-int32-decimal/disp32
    206     # . . discard args
    207     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    208     # check-stream-equal(_test-stream, "10", msg)
    209     # . . push args
    210     68/push  "F - test-write-int32-decimal-multiple-digits"/imm32
    211     68/push  "10"/imm32
    212     68/push  _test-stream/imm32
    213     # . . call
    214     e8/call  check-stream-equal/disp32
    215     # . . discard args
    216     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    217     # . end
    218     c3/return
    219
    220 test-write-int32-decimal-negative:
    221     # - check that a negative single-digit number converts correctly
    222     # setup
    223     # . clear-stream(_test-stream)
    224     # . . push args
    225     68/push  _test-stream/imm32
    226     # . . call
    227     e8/call  clear-stream/disp32
    228     # . . discard args
    229     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    230     # write-int32-decimal(_test-stream, -9)
    231     # . . push args
    232     68/push  -9/imm32
    233     68/push  _test-stream/imm32
    234     # . . call
    235     e8/call  write-int32-decimal/disp32
    236     # . . discard args
    237     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    238 +-- 26 lines: #?     # dump _test-stream ------------------------------------------------------------------------------------------------------------------------------------------------
    264     # check-stream-equal(_test-stream, "-9", msg)
    265     # . . push args
    266     68/push  "F - test-write-int32-decimal-negative"/imm32
    267     68/push  "-9"/imm32
    268     68/push  _test-stream/imm32
    269     # . . call
    270     e8/call  check-stream-equal/disp32
    271     # . . discard args
    272     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    273     # . end
    274     c3/return
    275
    276 test-write-int32-decimal-negative-multiple-digits:
    277     # - check that a multi-digit number converts correctly
    278     # setup
    279     # . clear-stream(_test-stream)
    280     # . . push args
    281     68/push  _test-stream/imm32
    282     # . . call
    283     e8/call  clear-stream/disp32
    284     # . . discard args
    285     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    286     # write-int32-decimal(_test-stream, -10)
    287     # . . push args
    288     68/push  -0xa/imm32
    289     68/push  _test-stream/imm32
    290     # . . call
    291     e8/call  write-int32-decimal/disp32
    292     # . . discard args
    293     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    294     # check-stream-equal(_test-stream, "-10", msg)
    295     # . . push args
    296     68/push  "F - test-write-int32-decimal-negative-multiple-digits"/imm32
    297     68/push  "-10"/imm32
    298     68/push  _test-stream/imm32
    299     # . . call
    300     e8/call  check-stream-equal/disp32
    301     # . . discard args
    302     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    303     # . end
    304     c3/return
    305
    306 decimal-digit?:  # c: grapheme -> result/eax: boolean
    307     # . prologue
    308     55/push-ebp
    309     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    310     # . save registers
    311     51/push-ecx
    312     # ecx = c
    313     8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           1/r32/ecx   8/disp8         .                 # copy *(ebp+8) to ecx
    314     # result = false
    315     b8/copy-to-eax  0/imm32/false
    316     # return false if c < '0'
    317     81          7/subop/compare     3/mod/direct    1/rm32/ecx    .           .             .           .           .               0x30/imm32        # compare ecx
    318     7c/jump-if-<  $decimal-digit?:end/disp8
    319     # return (c <= '9')
    320     81          7/subop/compare     3/mod/direct    1/rm32/ecx    .           .             .           .           .               0x39/imm32        # compare ecx
    321     7f/jump-if->  $decimal-digit?:end/disp8
    322 $decimal-digit?:true:
    323     b8/copy-to-eax  1/imm32/true
    324 $decimal-digit?:end:
    325     # . restore registers
    326     59/pop-to-ecx
    327     # . epilogue
    328     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    329     5d/pop-to-ebp
    330     c3/return
    331
    332 test-decimal-digit-below-0:
    333     # eax = decimal-digit?(0x2f)
    334     # . . push args
    335     68/push  0x2f/imm32
    336     # . . call
    337     e8/call  decimal-digit?/disp32
    338     # . . discard args
    339     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    340     # check-ints-equal(eax, 0, msg)
    341     # . . push args
    342     68/push  "F - test-decimal-digit-below-0"/imm32
    343     68/push  0/imm32/false
    344     50/push-eax
    345     # . . call
    346     e8/call  check-ints-equal/disp32
    347     # . . discard args
    348     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    349     c3/return
    350
    351 test-decimal-digit-0-to-9:
    352     # eax = decimal-digit?(0x30)
    353     # . . push args
    354     68/push  0x30/imm32
    355     # . . call
    356     e8/call  decimal-digit?/disp32
    357     # . . discard args
    358     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    359     # check-ints-equal(eax, 1, msg)
    360     # . . push args
    361     68/push  "F - test-decimal-digit-at-0"/imm32
    362     68/push  1/imm32/true
    363     50/push-eax
    364     # . . call
    365     e8/call  check-ints-equal/disp32
    366     # . . discard args
    367     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    368     # eax = decimal-digit?(0x39)
    369     # . . push args
    370     68/push  0x39/imm32
    371     # . . call
    372     e8/call  decimal-digit?/disp32
    373     # . . discard args
    374     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    375     # check-ints-equal(eax, 1, msg)
    376     # . . push args
    377     68/push  "F - test-decimal-digit-at-9"/imm32
    378     68/push  1/imm32/true
    379     50/push-eax
    380     # . . call
    381     e8/call  check-ints-equal/disp32
    382     # . . discard args
    383     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    384     c3/return
    385
    386 test-decimal-digit-above-9:
    387     # eax = decimal-digit?(0x3a)
    388     # . . push args
    389     68/push  0x3a/imm32
    390     # . . call
    391     e8/call  decimal-digit?/disp32
    392     # . . discard args
    393     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    394     # check-ints-equal(eax, 0, msg)
    395     # . . push args
    396     68/push  "F - test-decimal-digit-above-9"/imm32
    397     68/push  0/imm32/false
    398     50/push-eax
    399     # . . call
    400     e8/call  check-ints-equal/disp32
    401     # . . discard args
    402     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    403     c3/return
    404
    405 to-decimal-digit:  # in: grapheme -> out/eax: int
    406     # . prologue
    407     55/push-ebp
    408     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    409     # eax = in
    410     8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/eax   8/disp8         .                 # copy *(ebp+8) to eax
    411 $to-decimal-digit:check0:
    412     # if (eax < '0') goto abort
    413     3d/compare-eax-with  0x30/imm32/0
    414     7c/jump-if-<  $to-decimal-digit:abort/disp8
    415 $to-decimal-digit:check1:
    416     # if (eax > '9') goto abort
    417     3d/compare-eax-with  0x39/imm32/f
    418     7f/jump-if->  $to-decimal-digit:abort/disp8
    419 $to-decimal-digit:digit:
    420     # return eax - '0'
    421     2d/subtract-from-eax  0x30/imm32/0
    422 $to-decimal-digit:end:
    423     # . epilogue
    424     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    425     5d/pop-to-ebp
    426     c3/return
    427
    428 $to-decimal-digit:abort:
    429     # . write-buffered(stderr, error)
    430     # . . push args
    431     68/push  "to-decimal-digit: not a digit character: "/imm32
    432     68/push  Stderr/imm32
    433     # . . call
    434     e8/call  write-buffered/disp32
    435     # . . discard args
    436     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    437     # . write-byte-buffered(stderr, %eax)
    438     # . . push args
    439     50/push-eax
    440     68/push  Stderr/imm32
    441     # . . call
    442 #?     e8/call  write-byte-buffered/disp32
    443     e8/call  write-int32-hex-buffered/disp32
    444     # . . discard args
    445     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    446     # . write-buffered(stderr, "\n")
    447     # . . push args
    448     68/push  Newline/imm32
    449     68/push  Stderr/imm32
    450     # . . call
    451     e8/call  write-buffered/disp32
    452     # . . discard args
    453     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    454     # . flush(Stderr)
    455     # . . push args
    456     68/push  Stderr/imm32
    457     # . . call
    458     e8/call  flush/disp32
    459     # . . discard args
    460     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    461     # . syscall(exit, 1)
    462     bb/copy-to-ebx  1/imm32
    463     e8/call  syscall_exit/disp32
    464     # never gets here
    465
    466 # . . vim:nowrap:textwidth=0