1 # Port of https://github.com/akkartik/crenshaw/blob/master/tutor2.1.pas
  2 # which corresponds to the section "single digits" in https://compilers.iecc.com/crenshaw/tutor2.txt
  3 # except that we support hex digits.
  4 #
  5 # To run:
  6 #   $ bootstrap/bootstrap translate [01]*.subx apps/crenshaw2-1.subx -o apps/crenshaw2-1
  7 #   $ echo '3'  |bootstrap/bootstrap run crenshaw2-1
  8 # Expected output:
  9 #   # syscall(exit, 3)
 10 #   bb/copy-to-ebx  3/imm32
 11 #   b8/copy-to-eax  1/imm32/exit
 12 #   cd/syscall  0x80/imm8
 13 #
 14 # To run the generated output:
 15 #   $ echo '3'  |bootstrap/bootstrap run crenshaw2-1 > z1.subx
 16 #   $ bootstrap/bootstrap translate z1.subx -o z1
 17 #   $ bootstrap/bootstrap run z1
 18 #   $ echo $?
 19 #   3
 20 #
 21 # Stdin must contain just a single hex digit. Other input will print an error:
 22 #   $ echo 'xyz'  |bootstrap/bootstrap run crenshaw2-1
 23 #   Error: integer expected
 24 #
 25 # Names in this file sometimes follow Crenshaw's original rather than my usual
 26 # naming conventions.
 27 
 28 == code
 29 #   instruction                     effective address                                                   register    displacement    immediate
 30 # . op          subop               mod             rm32          base        index         scale       r32
 31 # . 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
 32 
 33 Entry:  # run tests if necessary, call 'compile' if not
 34     # . prologue
 35     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
 36 
 37     # initialize heap
 38     # . Heap = new-segment(Heap-size)
 39     # . . push args
 40     68/push  Heap/imm32
 41     ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Heap-size/disp32                  # push *Heap-size
 42     # . . call
 43     e8/call  new-segment/disp32
 44     # . . discard args
 45     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
 46 
 47     # - if argc > 1 and argv[1] == "test", then return run_tests()
 48     # if (argc <= 1) goto run-main
 49     81          7/subop/compare     1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0/disp8         1/imm32           # compare *ebp
 50     7e/jump-if-<=  $run-main/disp8
 51     # if (!kernel-string-equal?(argv[1], "test")) goto run-main
 52     # . eax = kernel-string-equal?(argv[1], "test")
 53     # . . push args
 54     68/push  "test"/imm32
 55     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         .                 # push *(ebp+8)
 56     # . . call
 57     e8/call  kernel-string-equal?/disp32
 58     # . . discard args
 59     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
 60     # . if (eax == false) goto run-main
 61     3d/compare-eax-and  0/imm32/false
 62     74/jump-if-=  $run-main/disp8
 63     # run-tests()
 64     e8/call  run-tests/disp32
 65     # syscall(exit, *Num-test-failures)
 66     8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           3/r32/ebx   Num-test-failures/disp32          # copy *Num-test-failures to ebx
 67     eb/jump  $main:end/disp8
 68 $run-main:
 69     # - otherwise read a program from stdin and emit its translation to stdout
 70     # . compile(Stdin, 1/stdout, 2/stderr, ed)
 71     # . . push args
 72     68/push  0/imm32/exit-descriptor
 73     68/push  2/imm32/stderr
 74     68/push  1/imm32/stdout
 75     68/push  Stdin/imm32
 76     # . . call
 77     e8/call  compile/disp32
 78     # . . discard args
 79     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0x10/imm32        # add to esp
 80     # syscall(exit, 0)
 81     bb/copy-to-ebx  0/imm32
 82 $main:end:
 83     e8/call  syscall_exit/disp32
 84 
 85 # the main entry point
 86 compile:  # in: (addr buffered-file), out: fd or (addr stream byte), err: fd or (addr stream byte), ed: (addr exit-descriptor)
 87     # . prologue
 88     55/push-ebp
 89     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
 90     # . save registers
 91     50/push-eax
 92     51/push-ecx
 93     # prime the pump
 94     # . Look = get-char(in)
 95     # . . push args
 96     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8      .                    # push *(ebp+8)
 97     # . . call
 98     e8/call  get-char/disp32
 99     # . . discard args
100     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
101     # var num/ecx: (stream byte 7)
102     # Numbers can be 32 bits or 8 hex bytes long. One of them will be in 'Look', so we need space for 7 bytes.
103     # Sizing the stream just right buys us overflow-handling for free inside 'get-num'.
104     # Add 12 bytes for 'read', 'write' and 'size' fields, for a total of 19 bytes, or 0x13 in hex.
105     # The stack pointer is no longer aligned, so dump_stack() can be misleading past this point.
106     81          5/subop/subtract    3/mod/direct    4/rm32/esp    .           .             .           .           .               0x13/imm32        # subtract from esp
107     89/copy                         3/mod/direct    1/rm32/ecx    .           .             .           4/r32/esp   .               .                 # copy esp to ecx
108     # initialize the stream
109     # . num->size = 7
110     c7          0/subop/copy        1/mod/*+disp8   1/rm32/ecx    .           .             .           .           8/disp8         7/imm32           # copy to *(ecx+8)
111     # . clear-stream(num)
112     # . . push args
113     51/push-ecx
114     # . . call
115     e8/call  clear-stream/disp32
116     # . . discard args
117     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
118     # read a digit from 'in' into 'num'
119     # . get-num(in, num, err, ed)
120     # . . push args
121     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0x14/disp8      .                 # push *(ebp+20)
122     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0x10/disp8      .                 # push *(ebp+16)
123     51/push-ecx/num
124     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8      .                    # push *(ebp+8)
125     # . . call
126     e8/call  get-num/disp32
127     # . . discard args
128     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0x10/imm32        # add to esp
129     # render 'num' into the following template on 'out':
130     #   bb/copy-to-ebx  _num_
131     #   b8/copy-to-eax  1/imm32/exit
132     #   cd/syscall  0x80/imm8
133     #
134     # . write(out, "bb/copy-to-ebx  ")
135     # . . push args
136     68/push  "bb/copy-to-ebx  "/imm32
137     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
138     # . . call
139     e8/call  write/disp32
140     # . . discard args
141     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
142     # . write-stream(out, num)
143     # . . push args
144     51/push-ecx/num
145     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
146     # . . call
147     e8/call  write-stream/disp32
148     # . . discard args
149     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
150     # . write(out, Newline)
151     # . . push args
152     68/push  Newline/imm32
153     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
154     # . . call
155     e8/call  write/disp32
156     # . . discard args
157     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
158     # . write(out, "b8/copy-to-eax  1/imm32/exit\n")
159     # . . push args
160     68/push  "b8/copy-to-eax  1/imm32/exit\n"/imm32
161     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
162     # . . call
163     e8/call  write/disp32
164     # . . discard args
165     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
166     # . write(out, "cd/syscall  0x80/imm8\n")
167     # . . push args
168     68/push  "cd/syscall  0x80/imm8\n"/imm32
169     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
170     # . . call
171     e8/call  write/disp32
172     # . . discard args
173     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
174 $compile:end:
175     # . restore registers
176     59/pop-to-ecx
177     58/pop-to-eax
178     # . epilogue
179     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
180     5d/pop-to-ebp
181     c3/return
182 
183 # Read a single digit into 'out'. Abort if there are none, or if there is no
184 # space in 'out'.
185 # Input comes from the global variable 'Look' (first byte) and the argument
186 # 'in' (rest). We leave the next byte from 'in' into 'Look' on exit.
187 get-num:  # in: (addr buffered-file), out: (addr stream byte), err: fd or (addr stream byte), ed: (addr exit-descriptor)
188     # pseudocode:
189     #   if (!digit?(Look)) expected(ed, err, "integer")
190     #   if out->write >= out->size
191     #     write(err, "Error: too many digits in number\n")
192     #     stop(ed, 1)
193     #   out->data[out->write] = LSB(Look)
194     #   ++out->write
195     #   Look = get-char(in)
196     #
197     # registers:
198     #   in: esi
199     #   out: edi
200     #   out->write: ecx (cached copy; need to keep in sync)
201     #   out->size: edx
202     #   temporaries: eax, ebx
203     # We can't allocate Look to a register because it gets written implicitly in
204     # get-char in each iteration of the loop. (Thereby demonstrating that it's
205     # not the right interface for us. But we'll keep it just to follow Crenshaw.)
206     #
207     # . prologue
208     55/push-ebp
209     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
210     # - if (digit?(Look)) expected(ed, err, "integer")
211     # . eax = digit?(Look)
212     # . . push args
213     ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Look/disp32     .                 # push *Look
214     # . . call
215     e8/call  digit?/disp32
216     # . . discard args
217     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
218     # . if (eax == false)
219     3d/compare-eax-and  0/imm32/false
220     75/jump-if-!=  $get-num:main/disp8
221     # . expected(ed, err, "integer")
222     # . . push args
223     68/push  "integer"/imm32
224     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0x10/disp8      .                 # push *(ebp+16)
225     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0x14/disp8      .                 # push *(ebp+20)
226     # . . call
227     e8/call  expected/disp32  # never returns
228     # . . discard args
229     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
230 $get-num:main:
231     # - otherwise read a digit
232     # . save registers
233     50/push-eax
234     51/push-ecx
235     52/push-edx
236     53/push-ebx
237     56/push-esi
238     57/push-edi
239     # read necessary variables to registers
240     # esi = in
241     8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           6/r32/esi   8/disp8         .                 # copy *(ebp+8) to esi
242     # edi = out
243     8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           7/r32/edi   0xc/disp8       .                 # copy *(ebp+12) to edi
244     # ecx = out->write
245     8b/copy                         0/mod/indirect  7/rm32/edi    .           .             .           1/r32/ecx   .               .                 # copy *edi to ecx
246     # edx = out->size
247     8b/copy                         1/mod/*+disp8   7/rm32/edi    .           .             .           2/r32/edx   8/disp8         .                 # copy *(edi+8) to edx
248 $get-num:loop:
249     # if (out->write >= out->size) error
250     39/compare                      3/mod/direct    2/rm32/edx    .           .             .           1/r32/ecx   .               .                 # compare edx with ecx
251     7d/jump-if-<  $get-num:stage2/disp8
252     # . error(ed, err, msg)  # TODO: show full number
253     # . . push args
254     68/push  "get-num: too many digits in number"/imm32
255     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0x10/disp8      .                 # push *(ebp+16)
256     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0x14/disp8      .                 # push *(ebp+20)
257     # . . call
258     e8/call  error/disp32  # never returns
259     # . . discard args
260     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
261 $get-num:stage2:
262     # out->data[out->write] = LSB(Look)
263     8d/copy-address                 1/mod/*+disp8   4/rm32/sib    7/base/edi  1/index/ecx   .           3/r32/ebx   0xc/disp8       .                 # copy edi+ecx+12 to ebx
264     8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/eax   Look/disp32     .                 # copy *Look to eax
265     88/copy-byte                    0/mod/indirect  3/rm32/ebx    .           .             .           0/r32/AL    .               .                 # copy byte at AL to *ebx
266     # ++out->write
267     41/increment-ecx
268     # Look = get-char(in)
269     # . . push args
270     56/push-esi
271     # . . call
272     e8/call  get-char/disp32
273     # . . discard args
274     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
275 $get-num:loop-end:
276     # persist necessary variables from registers
277     89/copy                         0/mod/indirect  7/rm32/edi    .           .             .           1/r32/ecx   .               .                 # copy ecx to *edi
278 $get-num:end:
279     # . restore registers
280     5f/pop-to-edi
281     5e/pop-to-esi
282     5b/pop-to-ebx
283     5a/pop-to-edx
284     59/pop-to-ecx
285     58/pop-to-eax
286     # . epilogue
287     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
288     5d/pop-to-ebp
289     c3/return
290 
291 test-get-num-reads-single-digit:
292     # - check that get-num returns first character if it's a digit
293     # This test uses exit-descriptors. Use ebp for setting up local variables.
294     55/push-ebp
295     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
296     # clear all streams
297     # . clear-stream(_test-stream)
298     # . . push args
299     68/push  _test-stream/imm32
300     # . . call
301     e8/call  clear-stream/disp32
302     # . . discard args
303     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
304     # . clear-stream($_test-buffered-file->buffer)
305     # . . push args
306     68/push  $_test-buffered-file->buffer/imm32
307     # . . call
308     e8/call  clear-stream/disp32
309     # . . discard args
310     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
311     # . clear-stream(_test-output-stream)
312     # . . push args
313     68/push  _test-output-stream/imm32
314     # . . call
315     e8/call  clear-stream/disp32
316     # . . discard args
317     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
318     # . clear-stream(_test-error-stream)
319     # . . push args
320     68/push  _test-error-stream/imm32
321     # . . call
322     e8/call  clear-stream/disp32
323     # . . discard args
324     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
325     # initialize 'in'
326     # . write(_test-stream, "3")
327     # . . push args
328     68/push  "3"/imm32
329     68/push  _test-stream/imm32
330     # . . call
331     e8/call  write/disp32
332     # . . discard args
333     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
334     # initialize exit-descriptor 'ed' for the call to 'get-num' below
335     # . var ed/eax: exit-descriptor
336     81          5/subop/subtract    3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # subtract from esp
337     89/copy                         3/mod/direct    0/rm32/eax    .           .             .           4/r32/esp   .               .                 # copy esp to eax
338     # . tailor-exit-descriptor(ed, 16)
339     # . . push args
340     68/push  0x10/imm32/nbytes-of-args-for-get-num
341     50/push-eax/ed
342     # . . call
343     e8/call  tailor-exit-descriptor/disp32
344     # . . discard args
345     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
346     # prime the pump
347     # . get-char(_test-buffered-file)
348     # . . push args
349     68/push  _test-buffered-file/imm32
350     # . . call
351     e8/call  get-char/disp32
352     # . . discard args
353     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
354     # get-num(in, out, err, ed)
355     # . . push args
356     50/push-eax/ed
357     68/push  _test-error-stream/imm32
358     68/push  _test-output-stream/imm32
359     68/push  _test-buffered-file/imm32
360     # . . call
361     e8/call  get-num/disp32
362     # registers except esp may be clobbered at this point
363     # . . discard args
364     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0x10/imm32        # add to esp
365     # check-ints-equal(*_test-output-stream->data, '3', msg)
366     # . . push args
367     68/push  "F - test-get-num-reads-single-digit"/imm32
368     68/push  0x33/imm32
369     b8/copy-to-eax  _test-output-stream/imm32
370     ff          6/subop/push        1/mod/*+disp8   0/rm32/eax    .           .             .           .           0xc/disp8       .                 # push *(eax+12)
371     # . . call
372     e8/call  check-ints-equal/disp32
373     # . . discard args
374     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
375     # . reclaim locals
376     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
377     5d/pop-to-ebp
378     c3/return
379 
380 test-get-num-aborts-on-non-digit-in-Look:
381     # - check that get-num returns first character if it's a digit
382     # This test uses exit-descriptors. Use ebp for setting up local variables.
383     55/push-ebp
384     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
385     # clear all streams
386     # . clear-stream(_test-stream)
387     # . . push args
388     68/push  _test-stream/imm32
389     # . . call
390     e8/call  clear-stream/disp32
391     # . . discard args
392     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
393     # . clear-stream($_test-buffered-file->buffer)
394     # . . push args
395     68/push  $_test-buffered-file->buffer/imm32
396     # . . call
397     e8/call  clear-stream/disp32
398     # . . discard args
399     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
400     # . clear-stream(_test-output-stream)
401     # . . push args
402     68/push  _test-output-stream/imm32
403     # . . call
404     e8/call  clear-stream/disp32
405     # . . discard args
406     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
407     # . clear-stream(_test-error-stream)
408     # . . push args
409     68/push  _test-error-stream/imm32
410     # . . call
411     e8/call  clear-stream/disp32
412     # . . discard args
413     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
414     # initialize 'in'
415     # . write(_test-stream, "3")
416     # . . push args
417     68/push  "3"/imm32
418     68/push  _test-stream/imm32
419     # . . call
420     e8/call  write/disp32
421     # . . discard args
422     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
423     # initialize exit-descriptor 'ed' for the call to 'get-num' below
424     # . var ed/eax: exit-descriptor
425     81          5/subop/subtract    3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # subtract from esp
426     89/copy                         3/mod/direct    0/rm32/eax    .           .             .           4/r32/esp   .               .                 # copy esp to eax
427     # . tailor-exit-descriptor(ed, 16)
428     # . . push args
429     68/push  0x10/imm32/nbytes-of-args-for-get-num
430     50/push-eax/ed
431     # . . call
432     e8/call  tailor-exit-descriptor/disp32
433     # . . discard args
434     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
435     # *don't* prime the pump
436     # get-num(in, out, err, ed)
437     # . . push args
438     50/push-eax/ed
439     68/push  _test-error-stream/imm32
440     68/push  _test-output-stream/imm32
441     68/push  _test-buffered-file/imm32
442     # . . call
443     e8/call  get-num/disp32
444     # registers except esp may be clobbered at this point
445     # . . discard args
446     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0x10/imm32        # add to esp
447     # check that get-num tried to call exit(1)
448     # . check-ints-equal(ed->value, 2, msg)  # i.e. stop was called with value 1
449     # . . push args
450     68/push  "F - test-get-num-aborts-on-non-digit-in-Look"/imm32
451     68/push  2/imm32
452     # . . push ed->value
453     ff          6/subop/push        1/mod/*+disp8   0/rm32/eax    .           .             .           .           4/disp8         .                 # push *(eax+4)
454     # . . call
455     e8/call  check-ints-equal/disp32
456     # . . discard args
457     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
458     # . reclaim locals
459     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
460     5d/pop-to-ebp
461     c3/return
462 
463 ## helpers
464 
465 # write(f, "Error: "+s+" expected\n") then stop(ed, 1)
466 expected:  # ed: (addr exit-descriptor), f: fd or (addr stream byte), s: (addr array byte)
467     # . prologue
468     55/push-ebp
469     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
470     # write(f, "Error: ")
471     # . . push args
472     68/push  "Error: "/imm32
473     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
474     # . . call
475     e8/call  write/disp32
476     # . . discard args
477     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
478     # write(f, s)
479     # . . push args
480     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0x10/disp8      .                 # push *(ebp+16)
481     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
482     # . . call
483     e8/call  write/disp32
484     # . . discard args
485     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
486     # write(f, " expected\n")
487     # . . push args
488     68/push  " expected\n"/imm32
489     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
490     # . . call
491     e8/call  write/disp32
492     # . . discard args
493     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
494     # stop(ed, 1)
495     # . . push args
496     68/push  1/imm32
497     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         .                 # push *(ebp+8)
498     # . . call
499     e8/call  stop/disp32
500     # should never get past this point
501 $expected:dead-end:
502     # . epilogue
503     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
504     5d/pop-to-ebp
505     c3/return
506 
507 # read a byte from 'f', and save it in 'Look'
508 get-char:  # f: (addr buffered-file)
509     # . prologue
510     55/push-ebp
511     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
512     # . save registers
513     50/push-eax
514     # eax = read-byte-buffered(f)
515     # . . push args
516     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         .                 # push *(ebp+8)
517     # . . call
518     e8/call  read-byte-buffered/disp32
519     # . . discard args
520     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
521     # save eax to Look
522     89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/eax   Look/disp32     .                 # copy eax to *Look
523 $get-char:end:
524     # . restore registers
525     58/pop-to-eax
526     # . epilogue
527     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
528     5d/pop-to-ebp
529     c3/return
530 
531 digit?:  # c: int -> eax: boolean
532     # . prologue
533     55/push-ebp
534     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
535     # eax = false
536     b8/copy-to-eax  0/imm32
537     # if (c < '0') return false
538     81          7/subop/compare     1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         0x30/imm32        # compare *(ebp+8)
539     7c/jump-if-<  $digit?:end/disp8
540     # if (c > '9') return false
541     81          7/subop/compare     1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         0x39/imm32        # compare *(ebp+8)
542     7f/jump-if->  $digit?:end/disp8
543     # otherwise return true
544     b8/copy-to-eax  1/imm32
545 $digit?:end:
546     # . epilogue
547     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
548     5d/pop-to-ebp
549     c3/return
550 
551 == data
552 
553 Look:  # (char with some extra padding)
554     0/imm32
555 
556 # . . vim:nowrap:textwidth=0