From 1a4de9dd58201bb57a07ea931d1764064fc52e64 Mon Sep 17 00:00:00 2001 From: Kartik Agaram Date: Sat, 22 Sep 2018 00:32:03 -0700 Subject: 4588 --- html/subx/examples/ex10.subx.html | 130 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 130 insertions(+) create mode 100644 html/subx/examples/ex10.subx.html (limited to 'html/subx/examples/ex10.subx.html') diff --git a/html/subx/examples/ex10.subx.html b/html/subx/examples/ex10.subx.html new file mode 100644 index 00000000..8ab82466 --- /dev/null +++ b/html/subx/examples/ex10.subx.html @@ -0,0 +1,130 @@ + + + + +Mu - subx/examples/ex10.subx + + + + + + + + + + +
+ 1 ## String comparison: return 1 iff the two args passed in at the commandline are equal.
+ 2 #
+ 3 # To run:
+ 4 #   $ subx translate ex10.subx ex10
+ 5 #   $ subx run ex10 abc abd
+ 6 # Expected result:
+ 7 #   $ echo $?
+ 8 #   0  # false
+ 9 
+10 == code
+11 # instruction                     effective address                                                   operand     displacement    immediate
+12 # op          subop               mod             rm32          base        index         scale       r32
+13 # 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
+14 
+15 # main: return argv_equal(argv[1], argv[2])
+16 #       At the start of a SubX program:
+17 #         argc: *ESP
+18 #         argv[0]: *(ESP+4)
+19 #         argv[1]: *(ESP+8)
+20 #         ...
+21   # s1 = argv[1] (EAX)
+22   8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none  .           0/r32/EAX   8/disp8         .                 # copy *(ESP+8) to EAX
+23   # s2 = argv[2] (EBX)
+24   8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none  .           3/r32/EBX   0xc/disp8       .                 # copy *(ESP+12) to EBX
+25   # call argv_equal(s1, s2)
+26     # push args
+27   50/push                         .               .             .           .             .           .           .               .                 # push EAX
+28   53/push                         .               .             .           .             .           .           .               .                 # push EBX
+29     # call
+30   e8/call argv_equal/disp32
+31   # exit(EAX)
+32 $exit:
+33   89/copy                         3/mod/direct    3/rm32/EBX    .           .             .           0/r32/EAX   .               .                 # copy EAX to EBX
+34   b8/copy                         .               .             .           .             .           .           .               1/imm32           # copy 1 to EAX
+35   cd/syscall  0x80/imm8
+36 
+37 # compare two null-terminated ascii strings
+38 # reason for the name: the only place we should have null-terminated ascii strings is from commandline args
+39 argv_equal:  # (s1, s2) : null-terminated ascii strings -> EAX : boolean
+40   # initialize s1 (ECX) and s2 (EDX)
+41   8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none  .           1/r32/ECX   8/disp8         .                 # copy *(ESP+8) to ECX
+42   8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none  .           2/r32/EDX   4/disp8         .                 # copy *(ESP+4) to EDX
+43   # while (true)
+44 $argv_loop:
+45     # c1/EAX, c2/EBX = *s1, *s2
+46   b8/copy  0/imm32  # clear EAX
+47   8a/copy                         0/mod/indirect  1/rm32/ECX    .           .             .           0/r32/EAX   .               .                 # copy byte at *ECX to lower byte of EAX
+48   bb/copy  0/imm32  # clear EBX
+49   8a/copy                         0/mod/indirect  2/rm32/EDX    .           .             .           3/r32/EBX   .               .                 # copy byte at *EDX to lower byte of EBX
+50     # if (c1 == 0) break
+51   3d/compare                      .               .             .           .             .           .           .               0/imm32           # compare EAX with 0
+52   74/jump-if-equal  $argv_break/disp8
+53     # if (c1 != c2) return false
+54   39/compare                      3/mod/direct    0/rm32/EAX    .           .             .           3/r32/EBX   .               .                 # compare EAX with EBX
+55   75/jump-if-not-equal  $argv_fail/disp8
+56     # ++s1, ++s2
+57   41/inc-ECX
+58   42/inc-EDX
+59   # end while
+60   eb/jump  $argv_loop/disp8
+61 $argv_break:
+62   # if (c2 == 0) return true
+63   81          7/subop/compare     3/mod/direct    3/rm32/EBX    .           .             .           .           .               0/imm32           # compare EBX with 0
+64   75/jump-if-not-equal  $argv_fail/disp8
+65   b8/copy                         .               .             .           .             .           .           .               1/imm32           # copy 1 to EAX
+66   c3/return
+67   # return false
+68 $argv_fail:
+69   b8/copy                         .               .             .           .             .           .           .               0/imm32           # copy 0 to EAX
+70   c3/return
+
+ + + -- cgit 1.4.1-2-gfad0