From 608a7fa8d0faf9a3e3d182d9eabe969804443aab Mon Sep 17 00:00:00 2001 From: Kartik Agaram Date: Fri, 7 Sep 2018 15:08:54 -0700 Subject: 4536 --- html/subx/apps/factorial.subx.html | 124 +++++++++++++++++++++++++++++++++++++ 1 file changed, 124 insertions(+) create mode 100644 html/subx/apps/factorial.subx.html (limited to 'html/subx/apps') diff --git a/html/subx/apps/factorial.subx.html b/html/subx/apps/factorial.subx.html new file mode 100644 index 00000000..c695cb3c --- /dev/null +++ b/html/subx/apps/factorial.subx.html @@ -0,0 +1,124 @@ + + + + +Mu - subx/apps/factorial.subx + + + + + + + + + + +
+ 1 ## compute the factorial of 5, and return the result in the exit code
+ 2 #
+ 3 # To run:
+ 4 #   $ subx translate apps/factorial.subx apps/factorial
+ 5 #   $ subx run apps/factorial
+ 6 # Expected result:
+ 7 #   $ echo $?
+ 8 #   120
+ 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:
+16   # prepare to make a call
+17   55/push                         .               .             .           .             .           .           .               .                 # push EBP
+18   89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
+19   # factorial(5)
+20   68/push                         .               .             .           .             .           .           .               5/imm32           # push 5
+21   e8/call                         .               .             .           .             .           .           factorial/disp32
+22   # discard arg
+23   5a/pop                          .               .             .           .             .           .           .               .                 # pop into EDX
+24   # clean up after call
+25   89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
+26   5d/pop                          .               .             .           .             .           .           .               .                 # pop to EBP
+27 
+28   # exit(EAX)
+29   89/copy                         3/mod/direct    3/rm32/EBX    .           .             .           0/r32/EAX   .               .                 # copy EAX to EBX
+30   b8/copy                         .               .             .           .             .           .           .               1/imm32           # copy 1 to EAX
+31   cd/syscall                      .               .             .           .             .           .           .               0x80/imm8         # int 80h
+32 
+33 # factorial(n)
+34 factorial:
+35   # initialize n
+36   8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none              2/r32/EDX   4/disp8         .                 # copy *(ESP+4) to EDX
+37   # initialize EAX to 1 (base case)
+38   b8/copy                         .               .             .           .             .           .           .               1/imm32           # copy 1 to EAX
+39   # if (n <= 1) jump exit
+40   81          7/subop/compare     3/mod/direct    2/rm32/EDX    .           .             .           .           .               1/imm32           # compare EDX with 1
+41   7e/jump-if-<=                   .               .             .           .             .           .           $factorial:exit/disp8             # jump if <= to $factorial:exit
+42   # EBX: n-1
+43   89/copy                         3/mod/direct    3/rm32/EBX    .           .             .           2/r32/EDX   .               .                 # copy EDX to EBX
+44   81          5/subop/subtract    3/mod/direct    3/rm32/EBX    .           .             .           .           .               1/imm32           # subtract 1 from EBX
+45   # prepare call
+46   55/push                         .               .             .           .             .           .           .               .                 # push EBP
+47   89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
+48   # EAX: factorial(n-1)
+49   53/push                         .               .             .           .             .           .           .               .                 # push EBX
+50   e8/call                         .               .             .           .             .           .           factorial/disp32
+51   # discard arg
+52   5e/pop                          .               .             .           .             .           .           .               .                 # pop into ESI
+53   # clean up after call
+54   89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
+55   5d/pop                          .               .             .           .             .           .           .               .                 # pop to EBP
+56   # refresh n
+57   8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none              2/r32/EDX   4/disp8         .                 # copy *(ESP+4) to EDX
+58   # return n * factorial(n-1)
+59   0f af/multiply                  3/mod/direct    2/rm32/EDX    .           .             .           0/r32/EAX   .               .                 # multiply EDX (n) into EAX (factorial(n-1))
+60   # TODO: check for overflow
+61 $factorial:exit:
+62   c3/return
+63 
+64 # vim:ft=subx:nowrap:so=0
+
+ + + -- cgit 1.4.1-2-gfad0