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 print-int32-decimal:  # out : (address stream), n : int32
  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->length]
 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     # . prolog
 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     # ten/ECX = 10
 48     b9/copy-to-ECX  0xa/imm32
 49     # push sentinel
 50     68/push  0/imm32/sentinel
 51     # EAX = 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-greater-or-equal  $print-int32-decimal:read-loop/disp8
 55 $print-int32-decimal:negative:
 56     f7          3/subop/negate      3/mod/direct    0/rm32/EAX    .           .             .           .           .               .                 # negate EAX
 57 $print-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-greater  $print-int32-decimal:read-loop/disp8
 68 $print-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-greater-or-equal  $print-int32-decimal:write/disp8
 72 $print-int32-decimal:push-negative:
 73     68/push  0x2d/imm32/-
 74 $print-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     # w/EDX = out->write
 78     8b/copy                         0/mod/indirect  7/rm32/EDI    .           .             .           2/r32/EDX   .               .                 # copy *EDI to EDX
 79     # curr/ECX = &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     # max/EBX = &out->data[out->length]
 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 $print-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-equal  $print-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-greater-or-equal-unsigned  $print-int32-decimal:abort/disp8
 93 $print-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  $print-int32-decimal:write-loop/disp8
101 $print-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 $print-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     # . epilog
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 $print-int32-decimal:abort:
117     # . _write(2/stderr, error)
118     # . . push args
119     68/push  "print-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     b8/copy-to-EAX  1/imm32/exit
128     cd/syscall  0x80/imm8
129     # never gets here
130 
131 test-print-int32-decimal:
132     # - check that a single-digit number converts correctly
133     # setup
134     # . clear-stream(_test-stream)
135     # . . push args
136     68/push  _test-stream/imm32
137     # . . call
138     e8/call  clear-stream/disp32
139     # . . discard args
140     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
141     # print-int32-decimal(_test-stream, 9)
142     # . . push args
143     68/push  9/imm32
144     68/push  _test-stream/imm32
145     # . . call
146     e8/call  print-int32-decimal/disp32
147     # . . discard args
148     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
149     # check-stream-equal(_test-stream, "9", msg)
150     # . . push args
151     68/push  "F - test-print-int32-decimal"/imm32
152     68/push  "9"/imm32
153     68/push  _test-stream/imm32
154     # . . call
155     e8/call  check-stream-equal/disp32
156     # . . discard args
157     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
158     # . end
159     c3/return
160 
161 test-print-int32-decimal-zero:
162     # - check that 0 converts correctly
163     # setup
164     # . clear-stream(_test-stream)
165     # . . push args
166     68/push  _test-stream/imm32
167     # . . call
168     e8/call  clear-stream/disp32
169     # . . discard args
170     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
171     # print-int32-decimal(_test-stream, 0)
172     # . . push args
173     68/push  0/imm32
174     68/push  _test-stream/imm32
175     # . . call
176     e8/call  print-int32-decimal/disp32
177     # . . discard args
178     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
179     # check-stream-equal(_test-stream, "0", msg)
180     # . . push args
181     68/push  "F - test-print-int32-decimal-zero"/imm32
182     68/push  "0"/imm32
183     68/push  _test-stream/imm32
184     # . . call
185     e8/call  check-stream-equal/disp32
186     # . . discard args
187     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
188     # . end
189     c3/return
190 
191 test-print-int32-decimal-multiple-digits:
192     # - check that a multi-digit number converts correctly
193     # setup
194     # . clear-stream(_test-stream)
195     # . . push args
196     68/push  _test-stream/imm32
197     # . . call
198     e8/call  clear-stream/disp32
199     # . . discard args
200     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
201     # print-int32-decimal(_test-stream, 10)
202     # . . push args
203     68/push  0xa/imm32
204     68/push  _test-stream/imm32
205     # . . call
206     e8/call  print-int32-decimal/disp32
207     # . . discard args
208     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
209     # check-stream-equal(_test-stream, "10", msg)
210     # . . push args
211     68/push  "F - test-print-int32-decimal-multiple-digits"/imm32
212     68/push  "10"/imm32
213     68/push  _test-stream/imm32
214     # . . call
215     e8/call  check-stream-equal/disp32
216     # . . discard args
217     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
218     # . end
219     c3/return
220 
221 test-print-int32-decimal-negative:
222     # - check that a negative single-digit number converts correctly
223     # setup
224     # . clear-stream(_test-stream)
225     # . . push args
226     68/push  _test-stream/imm32
227     # . . call
228     e8/call  clear-stream/disp32
229     # . . discard args
230     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
231     # print-int32-decimal(_test-stream, -9)
232     # . . push args
233     68/push  -9/imm32
234     68/push  _test-stream/imm32
235     # . . call
236     e8/call  print-int32-decimal/disp32
237     # . . discard args
238     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
239 +-- 26 lines: #?     # dump _test-stream ---------------------------------------------------------------------------------------------------------------------
265     # check-stream-equal(_test-stream, "-9", msg)
266     # . . push args
267     68/push  "F - test-print-int32-decimal-negative"/imm32
268     68/push  "-9"/imm32
269     68/push  _test-stream/imm32
270     # . . call
271     e8/call  check-stream-equal/disp32
272     # . . discard args
273     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
274     # . end
275     c3/return
276 
277 test-print-int32-decimal-negative-multiple-digits:
278     # - check that a multi-digit number converts correctly
279     # setup
280     # . clear-stream(_test-stream)
281     # . . push args
282     68/push  _test-stream/imm32
283     # . . call
284     e8/call  clear-stream/disp32
285     # . . discard args
286     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
287     # print-int32-decimal(_test-stream, -10)
288     # . . push args
289     68/push  -0xa/imm32
290     68/push  _test-stream/imm32
291     # . . call
292     e8/call  print-int32-decimal/disp32
293     # . . discard args
294     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
295     # check-stream-equal(_test-stream, "-10", msg)
296     # . . push args
297     68/push  "F - test-print-int32-decimal-negative-multiple-digits"/imm32
298     68/push  "-10"/imm32
299     68/push  _test-stream/imm32
300     # . . call
301     e8/call  check-stream-equal/disp32
302     # . . discard args
303     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
304     # . end
305     c3/return
306 
307 # . . vim:nowrap:textwidth=0