70 lines
3.6 KiB
Plaintext
70 lines
3.6 KiB
Plaintext
# String comparison: return 1 iff the two args passed in at the commandline are equal.
|
|
#
|
|
# To run:
|
|
# $ bootstrap/bootstrap translate apps/ex10.subx -o apps/ex10
|
|
# $ bootstrap/bootstrap run ex10 abc abd
|
|
# Expected result:
|
|
# $ echo $?
|
|
# 0 # false
|
|
|
|
== code
|
|
# instruction effective address register 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
|
|
|
|
Entry: # return argv-equal(argv[1], argv[2])
|
|
# At the start of a SubX program:
|
|
# argc: *esp
|
|
# argv[0]: *(esp+4)
|
|
# argv[1]: *(esp+8)
|
|
# ...
|
|
# . prologue
|
|
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
|
|
# argv-equal(argv[1], argv[2])
|
|
# . . push argv[2]
|
|
ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 0xc/disp8 . # push *(ebp+12)
|
|
# . . push argv[1]
|
|
ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8)
|
|
# . . call
|
|
e8/call argv-equal/disp32
|
|
# exit(eax)
|
|
89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx
|
|
e8/call syscall_exit/disp32
|
|
|
|
# compare two null-terminated ascii strings
|
|
# reason for the name: the only place we should have null-terminated ascii strings is from commandline args
|
|
argv-equal: # (s1, s2): null-terminated ascii strings -> eax: boolean
|
|
# initialize s1 (ecx) and s2 (edx)
|
|
8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 1/r32/ecx 4/disp8 . # copy *(esp+4) to ecx
|
|
8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 2/r32/edx 8/disp8 . # copy *(esp+8) to edx
|
|
$argv-equal:loop:
|
|
# c1/eax, c2/ebx = *s1, *s2
|
|
b8/copy-to-eax 0/imm32
|
|
8a/copy-byte 0/mod/indirect 1/rm32/ecx . . . 0/r32/AL . . # copy byte at *ecx to AL
|
|
bb/copy-to-ebx 0/imm32
|
|
8a/copy-byte 0/mod/indirect 2/rm32/edx . . . 3/r32/BL . . # copy byte at *edx to BL
|
|
# if (c1 == 0) break
|
|
3d/compare-eax-and 0/imm32/null
|
|
74/jump-if-= $argv-equal:break/disp8
|
|
# if (c1 != c2) return false
|
|
39/compare 3/mod/direct 0/rm32/eax . . . 3/r32/ebx . . # compare eax and ebx
|
|
75/jump-if-!= $argv-equal:false/disp8
|
|
# ++s1, ++s2
|
|
41/increment-ecx
|
|
42/increment-edx
|
|
# end while
|
|
eb/jump $argv-equal:loop/disp8
|
|
$argv-equal:break:
|
|
# if (c2 == 0) return true
|
|
81 7/subop/compare 3/mod/direct 3/rm32/ebx . . . . . 0/imm32/null # compare ebx
|
|
75/jump-if-!= $argv-equal:false/disp8
|
|
$argv-equal:success:
|
|
b8/copy-to-eax 1/imm32
|
|
c3/return
|
|
# return false
|
|
$argv-equal:false:
|
|
b8/copy-to-eax 0/imm32
|
|
c3/return
|
|
|
|
# . . vim:nowrap:textwidth=0
|