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 #   $ ./subx translate 0*.subx apps/crenshaw2-1.subx -o apps/crenshaw2-1
  7 #   $ echo '3'  |./subx run apps/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'  |./subx run apps/crenshaw2-1 > z1.subx
 16 #   $ ./subx translate z1.subx -o z1
 17 #   $ ./subx 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'  |./subx run apps/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     # initialize heap
 35     # . Heap = new-segment(64KB)
 36     # . . push args
 37     68/push  Heap/imm32
 38     68/push  0x10000/imm32/64KB
 39     # . . call
 40     e8/call  new-segment/disp32
 41     # . . discard args
 42     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
 43 
 44     # . prolog
 45     89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
 46     # - if argc > 1 and argv[1] == "test", then return run_tests()
 47     # . argc > 1
 48     81          7/subop/compare     1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0/disp8         1/imm32           # compare *EBP
 49     7e/jump-if-lesser-or-equal  $run-main/disp8
 50     # . argv[1] == "test"
 51     # . . push args
 52     68/push  "test"/imm32
 53     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         .                 # push *(EBP+8)
 54     # . . call
 55     e8/call  kernel-string-equal?/disp32
 56     # . . discard args
 57     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
 58     # . check result
 59     3d/compare-EAX-and  1/imm32
 60     75/jump-if-not-equal  $run-main/disp8
 61     # . run-tests()
 62     e8/call  run-tests/disp32
 63     8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           3/r32/EBX   Num-test-failures/disp32          # copy *Num-test-failures to EBX
 64     eb/jump  $main:end/disp8
 65 $run-main:
 66     # - otherwise read a program from stdin and emit its translation to stdout
 67     # var ed/EAX : exit-descriptor
 68     81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # subtract from ESP
 69     89/copy                         3/mod/direct    0/rm32/EAX    .           .             .           4/r32/ESP   .               .                 # copy ESP to EAX
 70     # configure ed to really exit()
 71     # . ed->target = 0
 72     c7          0/subop/copy        0/mod/direct    0/rm32/EAX    .           .             .           .           .               0/imm32           # copy to *EAX
 73     # return compile(Stdin, 1/stdout, 2/stderr, ed)
 74     # . . push args
 75     50/push-EAX/ed
 76     68/push  2/imm32/stderr
 77     68/push  1/imm32/stdout
 78     68/push  Stdin/imm32
 79     # . . call
 80     e8/call  compile/disp32
 81     # . . discard args
 82     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0x10/imm32        # add to ESP
 83     # . syscall(exit, 0)
 84     bb/copy-to-EBX  0/imm32
 85 $main:end:
 86     b8/copy-to-EAX  1/imm32/exit
 87     cd/syscall  0x80/imm8
 88 
 89 # the main entry point
 90 compile:  # in : (address buffered-file), out : fd or (address stream), err : fd or (address stream), ed : (address exit-descriptor) -> <void>
 91     # . prolog
 92     55/push-EBP
 93     89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
 94     # . save registers
 95     50/push-EAX
 96     51/push-ECX
 97     # prime the pump
 98     # . Look = get-char(in)
 99     # . . push args
100     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8      .                    # push *(EBP+8)
101     # . . call
102     e8/call  get-char/disp32
103     # . . discard args
104     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
105     # var num/ECX : (address stream) on the stack
106     # Numbers can be 32 bits or 8 hex bytes long. One of them will be in 'Look', so we need space for 7 bytes.
107     # Sizing the stream just right buys us overflow-handling for free inside 'get-num'.
108     # Add 12 bytes for 'read', 'write' and 'length' fields, for a total of 19 bytes, or 0x13 in hex.
109     # The stack pointer is no longer aligned, so dump_stack() can be misleading past this point.
110     81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               0x13/imm32        # subtract from ESP
111     89/copy                         3/mod/direct    1/rm32/ECX    .           .             .           4/r32/ESP   .               .                 # copy ESP to ECX
112     # initialize the stream
113     # . num->length = 7
114     c7          0/subop/copy        1/mod/*+disp8   1/rm32/ECX    .           .             .           .           8/disp8         7/imm32           # copy to *(ECX+8)
115     # . clear-stream(num)
116     # . . push args
117     51/push-ECX
118     # . . call
119     e8/call  clear-stream/disp32
120     # . . discard args
121     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
122     # read a digit from 'in' into 'num'
123     # . get-num(in, num, err, ed)
124     # . . push args
125     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x14/disp8      .                 # push *(EBP+20)
126     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x10/disp8      .                 # push *(EBP+16)
127     51/push-ECX/num
128     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8      .                    # push *(EBP+8)
129     # . . call
130     e8/call  get-num/disp32
131     # . . discard args
132     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0x10/imm32        # add to ESP
133     # render 'num' into the following template on 'out':
134     #   bb/copy-to-EBX  _num_
135     #   b8/copy-to-EAX  1/imm32/exit
136     #   cd/syscall  0x80/imm8
137     #
138     # . write(out, "bb/copy-to-EBX  ")
139     # . . push args
140     68/push  "bb/copy-to-EBX  "/imm32
141     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
142     # . . call
143     e8/call  write/disp32
144     # . . discard args
145     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
146     # . write-stream(out, num)
147     # . . push args
148     51/push-ECX/num
149     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
150     # . . call
151     e8/call  write-stream/disp32
152     # . . discard args
153     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
154     # . write(out, Newline)
155     # . . push args
156     68/push  Newline/imm32
157     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
158     # . . call
159     e8/call  write/disp32
160     # . . discard args
161     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
162     # . write(out, "b8/copy-to-EAX  1/imm32/exit\n")
163     # . . push args
164     68/push  "b8/copy-to-EAX  1/imm32/exit\n"/imm32
165     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
166     # . . call
167     e8/call  write/disp32
168     # . . discard args
169     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
170     # . write(out, "cd/syscall  0x80/imm8\n")
171     # . . push args
172     68/push  "cd/syscall  0x80/imm8\n"/imm32
173     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
174     # . . call
175     e8/call  write/disp32
176     # . . discard args
177     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
178 $compile:end:
179     # . restore registers
180     59/pop-to-ECX
181     58/pop-to-EAX
182     # . epilog
183     89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
184     5d/pop-to-EBP
185     c3/return
186 
187 # Read a single digit into 'out'. Abort if there are none, or if there is no space in 'out'.
188 # Input comes from the global variable 'Look', and we leave the next byte from
189 # 'in' into it on exit.
190 get-num:  # in : (address buffered-file), out : (address stream), err : fd or (address stream), ed : (address exit-descriptor) -> <void>
191     # pseudocode:
192     #   if (!is-digit?(Look)) expected(ed, err, "integer")
193     #   if out->write >= out->length
194     #     write(err, "Error: too many digits in number\n")
195     #     stop(ed, 1)
196     #   out->data[out->write] = LSB(Look)
197     #   ++out->write
198     #   Look = get-char(in)
199     #
200     # registers:
201     #   in: ESI
202     #   out: EDI
203     #   out->write: ECX (cached copy; need to keep in sync)
204     #   out->length: EDX
205     #   temporaries: EAX, EBX
206     # We can't allocate Look to a register because it gets written implicitly in
207     # get-char in each iteration of the loop. (Thereby demonstrating that it's
208     # not the right interface for us. But we'll keep it just to follow Crenshaw.)
209     #
210     # . prolog
211     55/push-EBP
212     89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
213     # - if (is-digit?(Look)) expected(ed, err, "integer")
214     # . EAX = is-digit?(Look)
215     # . . push args
216     ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Look/disp32     .                 # push *Look
217     # . . call
218     e8/call  is-digit?/disp32
219     # . . discard args
220     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
221     # . if (EAX == 0)
222     3d/compare-EAX-and  0/imm32
223     75/jump-if-not-equal  $get-num:main/disp8
224     # . expected(ed, err, "integer")
225     # . . push args
226     68/push  "integer"/imm32
227     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x10/disp8      .                 # push *(EBP+16)
228     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x14/disp8      .                 # push *(EBP+20)
229     # . . call
230     e8/call  expected/disp32  # never returns
231     # . . discard args
232     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
233 $get-num:main:
234     # - otherwise read a digit
235     # . save registers
236     50/push-EAX
237     51/push-ECX
238     52/push-EDX
239     53/push-EBX
240     56/push-ESI
241     57/push-EDI
242     # read necessary variables to registers
243     # ESI = in
244     8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .             .           6/r32/ESI   8/disp8         .                 # copy *(EBP+8) to ESI
245     # EDI = out
246     8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .             .           7/r32/EDI   0xc/disp8       .                 # copy *(EBP+12) to EDI
247     # ECX = out->write
248     8b/copy                         0/mod/indirect  7/rm32/EDI    .           .             .           1/r32/ECX   .               .                 # copy *EDI to ECX
249     # EDX = out->length
250     8b/copy                         1/mod/*+disp8   7/rm32/EDI    .           .             .           2/r32/EDX   8/disp8         .                 # copy *(EDI+8) to EDX
251     # if (out->write >= out->length) error
252     39/compare                      3/mod/direct    2/rm32/EDX    .           .             .           1/r32/ECX   .               .                 # compare EDX with ECX
253     7d/jump-if-lesser  $get-num:stage2/disp8
254     # . error(ed, err, msg)  # TODO: show full number
255     # . . push args
256     68/push  "get-num: too many digits in number"/imm32
257     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x10/disp8      .                 # push *(EBP+16)
258     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x14/disp8      .                 # push *(EBP+20)
259     # . . call
260     e8/call  error/disp32  # never returns
261     # . . discard args
262     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
263 $get-num:stage2:
264     # out->data[out->write] = LSB(Look)
265     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
266     8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/EAX   Look/disp32     .                 # copy *Look to EAX
267     88/copy-byte                    0/mod/indirect  3/rm32/EBX    .           .             .           0/r32/AL    .               .                 # copy byte at AL to *EBX
268     # ++out->write
269     41/increment-ECX
270     # Look = get-char(in)
271     # . . push args
272     56/push-ESI
273     # . . call
274     e8/call  get-char/disp32
275     # . . discard args
276     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
277 $get-num:loop-end:
278     # persist necessary variables from registers
279     89/copy                         0/mod/indirect  7/rm32/EDI    .           .             .           1/r32/ECX   .               .                 # copy ECX to *EDI
280 $get-num:end:
281     # . restore registers
282     5f/pop-to-EDI
283     5e/pop-to-ESI
284     5b/pop-to-EBX
285     5a/pop-to-EDX
286     59/pop-to-ECX
287     58/pop-to-EAX
288     # . epilog
289     89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
290     5d/pop-to-EBP
291     c3/return
292 
293 test-get-num-reads-single-digit:
294     # - check that get-num returns first character if it's a digit
295     # This test uses exit-descriptors. Use EBP for setting up local variables.
296     55/push-EBP
297     89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
298     # clear all streams
299     # . clear-stream(_test-stream)
300     # . . push args
301     68/push  _test-stream/imm32
302     # . . call
303     e8/call  clear-stream/disp32
304     # . . discard args
305     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
306     # . clear-stream(_test-buffered-file+4)
307     # . . push args
308     b8/copy-to-EAX  _test-buffered-file/imm32
309     05/add-to-EAX  4/imm32
310     50/push-EAX
311     # . . call
312     e8/call  clear-stream/disp32
313     # . . discard args
314     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
315     # . clear-stream(_test-output-stream)
316     # . . push args
317     68/push  _test-output-stream/imm32
318     # . . call
319     e8/call  clear-stream/disp32
320     # . . discard args
321     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
322     # . clear-stream(_test-error-stream)
323     # . . push args
324     68/push  _test-error-stream/imm32
325     # . . call
326     e8/call  clear-stream/disp32
327     # . . discard args
328     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
329     # initialize 'in'
330     # . write(_test-stream, "3")
331     # . . push args
332     68/push  "3"/imm32
333     68/push  _test-stream/imm32
334     # . . call
335     e8/call  write/disp32
336     # . . discard args
337     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
338     # initialize exit-descriptor 'ed' for the call to 'get-num' below
339     # . var ed/EAX : exit-descriptor
340     81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # subtract from ESP
341     89/copy                         3/mod/direct    0/rm32/EAX    .           .             .           4/r32/ESP   .               .                 # copy ESP to EAX
342     # . tailor-exit-descriptor(ed, 16)
343     # . . push args
344     68/push  0x10/imm32/nbytes-of-args-for-get-num
345     50/push-EAX/ed
346     # . . call
347     e8/call  tailor-exit-descriptor/disp32
348     # . . discard args
349     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
350     # prime the pump
351     # . get-char(_test-buffered-file)
352     # . . push args
353     68/push  _test-buffered-file/imm32
354     # . . call
355     e8/call  get-char/disp32
356     # . . discard args
357     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
358     # get-num(in, out, err, ed)
359     # . . push args
360     50/push-EAX/ed
361     68/push  _test-error-stream/imm32
362     68/push  _test-output-stream/imm32
363     68/push  _test-buffered-file/imm32
364     # . . call
365     e8/call  get-num/disp32
366     # registers except ESP may be clobbered at this point
367     # . . discard args
368     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0x10/imm32        # add to ESP
369     # check-ints-equal(*_test-output-stream->data, '3', msg)
370     # . . push args
371     68/push  "F - test-get-num-reads-single-digit"/imm32
372     68/push  0x33/imm32
373     b8/copy-to-EAX  _test-output-stream/imm32
374     ff          6/subop/push        1/mod/*+disp8   0/rm32/EAX    .           .             .           .           0xc/disp8       .                 # push *(EAX+12)
375     # . . call
376     e8/call  check-ints-equal/disp32
377     # . . discard args
378     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
379     # . reclaim locals
380     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
381     5d/pop-to-EBP
382     c3/return
383 
384 test-get-num-aborts-on-non-digit-in-Look:
385     # - check that get-num returns first character if it's a digit
386     # This test uses exit-descriptors. Use EBP for setting up local variables.
387     55/push-EBP
388     89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
389     # clear all streams
390     # . clear-stream(_test-stream)
391     # . . push args
392     68/push  _test-stream/imm32
393     # . . call
394     e8/call  clear-stream/disp32
395     # . . discard args
396     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
397     # . clear-stream(_test-buffered-file+4)
398     # . . push args
399     b8/copy-to-EAX  _test-buffered-file/imm32
400     05/add-to-EAX  4/imm32
401     50/push-EAX
402     # . . call
403     e8/call  clear-stream/disp32
404     # . . discard args
405     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
406     # . clear-stream(_test-output-stream)
407     # . . push args
408     68/push  _test-output-stream/imm32
409     # . . call
410     e8/call  clear-stream/disp32
411     # . . discard args
412     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
413     # . clear-stream(_test-error-stream)
414     # . . push args
415     68/push  _test-error-stream/imm32
416     # . . call
417     e8/call  clear-stream/disp32
418     # . . discard args
419     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
420     # initialize 'in'
421     # . write(_test-stream, "3")
422     # . . push args
423     68/push  "3"/imm32
424     68/push  _test-stream/imm32
425     # . . call
426     e8/call  write/disp32
427     # . . discard args
428     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
429     # initialize exit-descriptor 'ed' for the call to 'get-num' below
430     # . var ed/EAX : (address exit-descriptor)
431     81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # subtract from ESP
432     89/copy                         3/mod/direct    0/rm32/EAX    .           .             .           4/r32/ESP   .               .                 # copy ESP to EAX
433     # . tailor-exit-descriptor(ed, 16)
434     # . . push args
435     68/push  0x10/imm32/nbytes-of-args-for-get-num
436     50/push-EAX/ed
437     # . . call
438     e8/call  tailor-exit-descriptor/disp32
439     # . . discard args
440     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
441     # *don't* prime the pump
442     # get-num(in, out, err, ed)
443     # . . push args
444     50/push-EAX/ed
445     68/push  _test-error-stream/imm32
446     68/push  _test-output-stream/imm32
447     68/push  _test-buffered-file/imm32
448     # . . call
449     e8/call  get-num/disp32
450     # registers except ESP may be clobbered at this point
451     # . . discard args
452     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0x10/imm32        # add to ESP
453     # check that get-num tried to call exit(1)
454     # . check-ints-equal(ed->value, 2, msg)  # i.e. stop was called with value 1
455     # . . push args
456     68/push  "F - test-get-num-aborts-on-non-digit-in-Look"/imm32
457     68/push  2/imm32
458     # . . push ed->value
459     ff          6/subop/push        1/mod/*+disp8   0/rm32/EAX    .           .             .           .           4/disp8         .                 # push *(EAX+4)
460     # . . call
461     e8/call  check-ints-equal/disp32
462     # . . discard args
463     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
464     # . reclaim locals
465     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
466     5d/pop-to-EBP
467     c3/return
468 
469 ## helpers
470 
471 # write(f, "Error: "+s+" expected\n") then stop(ed, 1)
472 expected:  # ed : (address exit-descriptor), f : fd or (address stream), s : (address array byte) -> <void>
473     # . prolog
474     55/push-EBP
475     89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
476     # write(f, "Error: ")
477     # . . push args
478     68/push  "Error: "/imm32
479     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
480     # . . call
481     e8/call  write/disp32
482     # . . discard args
483     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
484     # write(f, s)
485     # . . push args
486     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x10/disp8      .                 # push *(EBP+16)
487     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
488     # . . call
489     e8/call  write/disp32
490     # . . discard args
491     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
492     # write(f, " expected")
493     # . . push args
494     68/push  " expected\n"/imm32
495     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
496     # . . call
497     e8/call  write/disp32
498     # . . discard args
499     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
500     # stop(ed, 1)
501     # . . push args
502     68/push  1/imm32
503     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         .                 # push *(EBP+8)
504     # . . call
505     e8/call  stop/disp32
506     # should never get past this point
507 $expected:dead-end:
508     # . epilog
509     89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
510     5d/pop-to-EBP
511     c3/return
512 
513 # read a byte from 'f', and save it in 'Look'
514 get-char:  # f : (address buffered-file) -> <void>
515     # . prolog
516     55/push-EBP
517     89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
518     # . save registers
519     50/push-EAX
520     # EAX = read-byte-buffered(f)
521     # . . push args
522     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         .                 # push *(EBP+8)
523     # . . call
524     e8/call  read-byte-buffered/disp32
525     # . . discard args
526     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
527     # save EAX to Look
528     89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/EAX   Look/disp32     .                 # copy EAX to *Look
529 $get-char:end:
530     # . restore registers
531     58/pop-to-EAX
532     # . epilog
533     89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
534     5d/pop-to-EBP
535     c3/return
536 
537 is-digit?:  # c : int -> EAX : boolean
538     # . prolog
539     55/push-EBP
540     89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
541     # EAX = false
542     b8/copy-to-EAX  0/imm32
543     # if (c < '0') return false
544     81          7/subop/compare     1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         0x30/imm32        # compare *(EBP+8)
545     7c/jump-if-lesser  $is-digit?:end/disp8
546     # if (c > '9') return false
547     81          7/subop/compare     1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         0x39/imm32        # compare *(EBP+8)
548     7f/jump-if-greater  $is-digit?:end/disp8
549     # otherwise return true
550     b8/copy-to-EAX  1/imm32
551 $is-digit?:end:
552     # . epilog
553     89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
554     5d/pop-to-EBP
555     c3/return
556 
557 == data
558 
559 Look:  # (char with some extra padding)
560     0/imm32
561 
562 # . . vim:nowrap:textwidth=0