about summary refs log tree commit diff stats
path: root/subx/apps/factorial.subx
blob: b4f8867ebc4e0682cd5b946638c4d96176ece164 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
## compute the factorial of 5, and return the result in the exit code
#
# To run:
#   $ subx translate apps/factorial.subx apps/factorial
#   $ subx run apps/factorial
# Expected result:
#   $ echo $?
#   120
#
# You can also run the automated test suite:
#   $ subx run apps/factorial test
# Expected output:
#   ........
# Every '.' indicates a passing test. Failing tests get a 'F'.
# When running tests the exit status doesn't mean anything. Yet.

== code
# instruction                     effective address                                                   operand     displacement    immediate
# op          subop               mod             rm32          base        index         scale       r32
# 1-3 bytes   3 bits              2 bits          3 bits        3 bits      3 bits        2 bits      2 bits      0/1/2/4 bytes   0/1/2/4 bytes

# main:
  # prolog
  89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
  # if (argc > 1)
  81          7/subop/compare     1/mod/*+disp8   4/rm32/SIB    5/base/EBP  4/index/none  .           .           0/disp8         1/imm32           # compare *EBP with 1
  7e/jump-if-lesser-or-equal  $run_main/disp8
  # and if (argv[1] == "test")
    # push args
  68/push  "test"/imm32
  ff          6/subop/push        1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           .           0x8/disp8       .                 # push *(EBP+8)
    # call
  e8/call  argv_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add 8 to ESP
    # check result
  3d/compare                      .               .             .           .             .           .           .               1/imm32           # compare EAX with 1
  75/jump-if-not-equal  $run_main/disp8
  # then
  e8/call  run_tests/disp32
  eb/jump  $main_exit/disp8
  # else EAX <- factorial(5)
$run_main:
    # push arg
  68/push  5/imm32
    # EAX <- call
  e8/call  factorial/disp32
    # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add 4 to ESP
$main_exit:
  # exit(EAX)
  89/copy                         3/mod/direct    3/rm32/EBX    .           .             .           0/r32/EAX   .               .                 # copy EAX to EBX
  b8/copy                         .               .             .           .             .           .           .               1/imm32           # copy 1 to EAX
  cd/syscall  0x80/imm8

# factorial(n)
factorial:
  # prolog
  55/push-EBP
  89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
  53/push-EBX
  # initialize EAX to 1 (base case)
  b8/copy                         .               .             .           .             .           .           .               1/imm32           # copy 1 to EAX
  # if (n <= 1) jump exit
  81          7/subop/compare     1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           .           8/disp8         1/imm32           # compare *(EBP+8) with 1
  7e/jump-if-<=  $factorial:exit/disp8
  # EBX: n-1
  8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none              3/r32/EBX   8/disp8         .                 # copy *(EBP+8) to EBX
  81          5/subop/subtract    3/mod/direct    3/rm32/EBX    .           .             .           .           .               1/imm32           # subtract 1 from EBX
  # EAX: factorial(n-1)
  53/push-EBX
  e8/call                         .               .             .           .             .           .           factorial/disp32
  # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add 4 to ESP
  # return n * factorial(n-1)
  f7          4/subop/multiply    1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none                          8/disp8         .                 # multiply *(EBP+8) into EAX
  # TODO: check for overflow
$factorial:exit:
  # epilog
  5b/pop-to-EBX
  89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
  5d/pop-to-EBP
  c3/return

test_factorial:
  # factorial(5)
    # push arg
  68/push  5/imm32
    # call
  e8/call  factorial/disp32
    # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add 4 to ESP
  # check_ints_equal(EAX, 120, failure message)
    # push args
  68/push  "F - test_factorial"/imm32
  68/push  0x78/imm32/expected-120
  50/push-EAX
    # call
  e8/call  check_ints_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add 12 to ESP
  # end
  c3/return

## helpers

# print msg to stderr if a != b, otherwise print "."
check_ints_equal:  # (a : int, b : int, msg : (address array byte)) -> boolean
  # prolog
  55/push-EBP
  89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
  # save registers
  51/push-ECX
  53/push-EBX
  # load args into EAX, EBX and ECX
  8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           0/r32/EAX   0x8/disp8       .                 # copy *(EBP+8) to EAX
  8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           3/r32/EBX   0xc/disp8       .                 # copy *(EBP+12) to EBX
  # if EAX == b/EBX
  39/compare                      3/mod/direct    0/rm32/EAX    .           .             .           3/r32/EBX   .               .                 # compare EAX and EBX
  75/jump-if-unequal  $check_ints_equal:else/disp8
    # print('.')
      # push args
  68/push  "."/imm32
      # call
  e8/call  write_stderr/disp32
      # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add 4 to ESP
    # return
  eb/jump  $check_ints_equal:end/disp8
  # else:
$check_ints_equal:else:
  # copy msg into ECX
  8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           1/r32/ECX   0x10/disp8       .                # copy *(EBP+16) to ECX
    # print(ECX)
      # push args
  51/push-ECX
      # call
  e8/call  write_stderr/disp32
      # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add 4 to ESP
    # print newline
      # push args
  68/push  Newline/imm32
      # call
  e8/call  write_stderr/disp32
      # discard arg
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add 4 to ESP
$check_ints_equal:end:
  # restore registers
  5b/pop-to-EBX
  59/pop-to-ECX
  # end
  89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
  5d/pop-to-EBP
  c3/return

# compare a null-terminated ascii string with a more idiomatic length-prefixed byte array
# reason for the name: the only place we should have null-terminated ascii strings is from commandline args
argv_equal:  # s : null-terminated ascii string, benchmark : length-prefixed ascii string -> EAX : boolean
  # prolog
  55/push-EBP
  89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
  # save registers
  51/push-ECX
  52/push-EDX
  53/push-EBX
  56/push-ESI
  57/push-EDI

  # pseudocode:
  #   initialize n = b.length
  #   initialize s1 = s
  #   initialize s2 = b.data
  #   i = 0
  #   for (i = 0; i < n; ++n)
  #     c1 = *s1
  #     c2 = *s2
  #     if c1 == 0
  #       return false
  #     if c1 != c2
  #       return false
  #   return *s1 == 0
# {{{
  # initialize s into EDI
  8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           7/r32/EDI   8/disp8         .                 # copy *(EBP+8) to EDI
  # initialize benchmark length n into EDX
  8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           2/r32/EDX   0xc/disp8       .                 # copy *(EBP+12) to EDX
  8b/copy                         0/mod/indirect  2/rm32/EDX    .           .             .           2/r32/EDX   .               .                 # copy *EDX to EDX
  # initialize benchmark data into ESI
  8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           6/r32/ESI   0xc/disp8       .                 # copy *(EBP+12) to ESI
  81          0/subop/add         3/mod/direct    6/rm32/ESI    .           .             .           .           .               4/imm32           # add 4 to ESI
  # initialize loop counter i into ECX
  b9/copy                         .               .             .           .             .           .           .               0/imm32/exit      # copy 1 to ECX
  # while (i/ECX < n/EDX)
$argv_loop:
  39/compare                      3/mod/direct    1/rm32/ECX    .           .             .           2/r32/EDX   .               .                 # compare ECX with EDX
  74/jump-if-equal  $argv_break/disp8
    # c1/EAX, c2/EBX = *s, *benchmark
  b8/copy  0/imm32  # clear EAX
  8a/copy                         0/mod/indirect  7/rm32/EDI    .           .             .           0/r32/EAX   .               .                 # copy byte at *EDI to lower byte of EAX
  bb/copy  0/imm32  # clear EBX
  8a/copy                         0/mod/indirect  6/rm32/ESI    .           .             .           3/r32/EBX   .               .                 # copy byte at *ESI to lower byte of EBX
    # if (c1 == 0) return false
  3d/compare                      .               .             .           .             .           .           .               0/imm32           # compare EAX with 0
  74/jump-if-equal  $argv_fail/disp8
    # if (c1 != c2) return false
  39/compare                      3/mod/direct    0/rm32/EAX    .           .             .           3/r32/EBX   .               .                 # compare EAX with EBX
  75/jump-if-not-equal  $argv_fail/disp8
    # ++s1, ++s2, ++i
  41/inc-ECX
  46/inc-ESI
  47/inc-EDI
  # end while
  eb/jump  $argv_loop/disp8
$argv_break:
  # if (*s/EDI == 0) return true
  b8/copy  0/imm32  # clear EAX
  8a/copy                         0/mod/indirect  7/rm32/EDI    .           .             .           0/r32/EAX   .               .                 # copy byte at *EDI to lower byte of EAX
  81          7/subop/compare     3/mod/direct    0/rm32/EAX    .           .             .           .           .               0/imm32           # compare EAX with 0
  75/jump-if-not-equal  $argv_fail/disp8
  b8/copy                         .               .             .           .             .           .           .               1/imm32           # copy 1 to EAX
  eb/jump  $argv_end/disp8
  # return false
$argv_fail:
  b8/copy                         .               .             .           .             .           .           .               0/imm32           # copy 0 to EAX

$argv_end:
  # restore registers
  5f/pop-to-EDI
  5e/pop-to-ESI
  5b/pop-to-EBX
  5a/pop-to-EDX
  59/pop-to-ECX
  # end
  89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
  5d/pop-to-EBP
  c3/return
# }}}
# tests for argv_equal {{{
test_compare_null_argv_with_empty_array:
  # EAX = argv_equal(Null_argv, "")
    # push args
  68/push  ""/imm32
  68/push  Null_argv/imm32
    # call
  e8/call  argv_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add 8 to ESP
  # call check_ints_equal(EAX, 1, msg)
    # push args
  68/push  "F - test_compare_null_argv_with_empty_array"/imm32
  68/push  1/imm32/true
  50/push-EAX
    # call
  e8/call  check_ints_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add 12 to ESP
  c3/return

test_compare_null_argv_with_non_empty_array:
  # EAX = argv_equal(Null_argv, "Abc")
    # push args
  68/push  "Abc"/imm32
  68/push  Null_argv/imm32
    # call
  e8/call  argv_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add 8 to ESP
  # call check_ints_equal(EAX, 0, msg)
    # push args
  68/push  "F - test_compare_null_argv_with_non_empty_array"/imm32
  68/push  0/imm32/false
  50/push-EAX
    # call
  e8/call  check_ints_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add 12 to ESP
  c3/return

test_compare_argv_with_equal_array:
  # EAX = argv_equal(Abc_argv, "Abc")
    # push args
  68/push  "Abc"/imm32
  68/push  Abc_argv/imm32
    # call
  e8/call  argv_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add 8 to ESP
  # call check_ints_equal(EAX, 1, msg)
    # push args
  68/push  "F - test_compare_argv_with_equal_array"/imm32
  68/push  1/imm32/true
  50/push-EAX
    # call
  e8/call  check_ints_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add 12 to ESP
  c3/return

test_compare_argv_with_inequal_array:
  # EAX = argv_equal(Abc_argv, "Adc")
    # push args
  68/push  "Adc"/imm32
  68/push  Abc_argv/imm32
    # call
  e8/call  argv_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add 8 to ESP
  # call check_ints_equal(EAX, 0, msg)
    # push args
  68/push  "F - test_compare_argv_with_equal_array"/imm32
  68/push  0/imm32/false
  50/push-EAX
    # call
  e8/call  check_ints_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add 12 to ESP
  c3/return

test_compare_argv_with_empty_array:
  # EAX = argv_equal(Abc_argv, "")
    # push args
  68/push  ""/imm32
  68/push  Abc_argv/imm32
    # call
  e8/call  argv_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add 8 to ESP
  # call check_ints_equal(EAX, 0)
    # push args
  68/push  "F - test_compare_argv_with_equal_array"/imm32
  68/push  0/imm32/false
  50/push-EAX
    # call
  e8/call  check_ints_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add 12 to ESP
  c3/return

test_compare_argv_with_shorter_array:
  # EAX = argv_equal(Abc_argv, "Ab")
    # push args
  68/push  "Ab"/imm32
  68/push  Abc_argv/imm32
    # call
  e8/call  argv_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add 8 to ESP
  # call check_ints_equal(EAX, 0)
    # push args
  68/push  "F - test_compare_argv_with_shorter_array"/imm32
  68/push  0/imm32/false
  50/push-EAX
    # call
  e8/call  check_ints_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add 12 to ESP
  c3/return

test_compare_argv_with_longer_array:
  # EAX = argv_equal(Abc_argv, "Abcd")
    # push args
  68/push  "Abcd"/imm32
  68/push  Abc_argv/imm32
    # call
  e8/call  argv_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add 8 to ESP
  # call check_ints_equal(EAX, 0)
    # push args
  68/push  "F - test_compare_argv_with_longer_array"/imm32
  68/push  0/imm32/false
  50/push-EAX
    # call
  e8/call  check_ints_equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add 12 to ESP
  c3/return
# }}}

write_stderr:  # s : (address array byte) -> <void>
  # prolog
  55/push-EBP
  89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
  # save registers
  50/push-EAX
  51/push-ECX
  52/push-EDX
  53/push-EBX
  # write(2/stderr, (data) s+4, (size) *s)
    # fd = 2 (stderr)
  bb/copy                         .               .             .           .             .           .           .               2/imm32           # copy 2 to EBX
    # x = s+4
  8b/copy                         1/mod/*+disp8   4/rm32/SIB    5/base/EBP  4/index/none  .           1/r32/ECX   8/disp8         .                 # copy *(EBP+8) to ECX
  81          0/subop/add         3/mod/direct    1/rm32/ECX    .           .             .           .           .               4/imm32           # add 4 to ECX
    # size = *s
  8b/copy                         1/mod/*+disp8   4/rm32/SIB    5/base/EBP  4/index/none  .           2/r32/EDX   8/disp8         .                 # copy *(EBP+8) to EDX
  8b/copy                         0/mod/indirect  2/rm32/EDX    .           .             .           2/r32/EDX   .               .                 # copy *EDX to EDX
    # call write()
  b8/copy                         .               .             .           .             .           .           .               4/imm32/write     # copy 1 to EAX
  cd/syscall  0x80/imm8
  # restore registers
  5b/pop-to-EBX
  5a/pop-to-EDX
  59/pop-to-ECX
  58/pop-to-EAX
  # end
  89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
  5d/pop-to-EBP
  c3/return

== data
Newline:
  # size
  01 00 00 00
  # data
  0a/newline

# for argv_equal tests
Null_argv:
  00/null
Abc_argv:
  41/A 62/b 63/c 00/null

# vim:ft=subx:nowrap:so=0