2018-10-03 05:16:59 +00:00
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# Comparing 'regular' length-prefixed strings.
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== code
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# instruction effective address operand displacement immediate
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# op subop mod rm32 base index scale r32
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# 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
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# main: (manual test if this is the last file loaded)
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e8/call run_tests/disp32 # 'run_tests' is a function created automatically by SubX. It calls all functions that start with 'test_'.
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# exit(EAX)
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89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX
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b8/copy . . . . . . . 1/imm32 # copy to EAX
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cd/syscall 0x80/imm8
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string_equal: # s : string, benchmark : string -> EAX : boolean
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# prolog
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55/push-EBP
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89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP
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# save registers
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51/push-ECX
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52/push-EDX
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53/push-EBX
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56/push-ESI
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# pseudocode:
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# if s.length != b.length return false
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2018-10-05 06:01:52 +00:00
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# for i = 0; i < s.length; ++i
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2018-10-03 05:16:59 +00:00
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# if s[i] != b[i] return false
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# return true
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# registers:
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# i: ECX
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# s.length: EDX
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# b.length: EBX
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# b[i]: EBX
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# s[i]: EAX
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#
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# var s/EAX : (address array byte)
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8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 0/r32/EAX 8/disp8 . # copy *(EBP+8) to EAX
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# var benchmark/EBX : (address array byte)
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8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 3/r32/EBX 0xc/disp8 . # copy *(EBP+12) to EBX
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# if s.length != b.length return false
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# EDX = s.length
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8b/copy 0/mod/indirect 0/rm32/EAX . . . 2/r32/EDX . . # copy *EAX to EDX
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# compare s.length and b.length
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39/compare 0/mod/indirect 3/rm32/EBX . . . 2/r32/EDX . . # compare *EBX with EDX
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75/jump-if-not-equal $string_not_equal/disp8
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$string_lengths_equal:
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# var i/ECX : int = 0
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b9/copy . . . . . . . 0/imm32 # copy to ECX
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# EBX = &b[i]
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43/inc-EBX
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# EAX = &s[i]
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40/inc-EAX
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$string_equal_loop:
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# if i >= s.length return true
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39/compare 3/mod/direct 1/rm32/ECX . . . 2/r32/EDX . . # compare ECX with EDX
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7d/jump-if-greater-or-equal $string_equal/disp8
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# if b[i] != s[i] return false
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# ESI = s[i]
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8b/copy 0/mod/indirect 0/rm32/EAX . . . 6/r32/ESI . . # copy *EAX to ESI
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# compare b[i] with ESI
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39/compare 0/mod/indirect 3/rm32/EBX . . . 6/r32/ESI . . # compare *EBX with ESI
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75/jump-if-not-equal $string_not_equal/disp8
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# ++i
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41/inc-ECX
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40/inc-EAX
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43/inc-EBX
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# loop
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eb/jump $string_equal_loop/disp8
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$string_equal:
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# return true
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b8/copy . . . . . . . 1/imm32 # copy to EAX
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eb/jump $string_equal_end/disp8
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$string_not_equal:
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# return false
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b8/copy . . . . . . . 0/imm32 # copy to EAX
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$string_equal_end:
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# restore registers
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5e/pop-to-ESI
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5b/pop-to-EBX
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5a/pop-to-EDX
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59/pop-to-ECX
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# epilog
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89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP
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5d/pop-to-EBP
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c3/return
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## tests
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test_compare_empty_with_empty_string:
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# EAX = string_equal("", "")
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# push args
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68/push ""/imm32
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68/push ""/imm32
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# call
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e8/call string_equal/disp32
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# discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
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# call check_ints_equal(EAX, 1, msg)
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# push args
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68/push "F - test_compare_empty_with_empty_string"/imm32
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68/push 1/imm32/true
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50/push-EAX
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# call
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e8/call check_ints_equal/disp32
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# discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
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c3/return
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test_compare_empty_with_non_empty_string: # also checks length-mismatch code path
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# EAX = string_equal("", "Abc")
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# push args
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68/push "Abc"/imm32
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68/push ""/imm32
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# call
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2018-10-04 03:47:07 +00:00
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e8/call string_equal/disp32
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2018-10-03 05:16:59 +00:00
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# discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
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# call check_ints_equal(EAX, 0, msg)
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# push args
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68/push "F - test_compare_empty_with_non_empty_string"/imm32
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68/push 0/imm32/false
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50/push-EAX
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# call
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e8/call check_ints_equal/disp32
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# discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
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c3/return
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test_compare_equal_strings:
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2018-10-04 03:47:07 +00:00
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# EAX = string_equal("Abc", "Abc")
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2018-10-03 05:16:59 +00:00
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# push args
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68/push "Abc"/imm32
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68/push "Abc"/imm32
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# call
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e8/call string_equal/disp32
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# discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
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# call check_ints_equal(EAX, 1, msg)
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# push args
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68/push "F - test_compare_equal_strings"/imm32
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68/push 1/imm32/true
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50/push-EAX
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# call
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e8/call check_ints_equal/disp32
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# discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
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c3/return
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test_compare_inequal_strings_equal_lengths:
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2018-10-04 03:47:07 +00:00
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# EAX = string_equal("Abc", "Adc")
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2018-10-03 05:16:59 +00:00
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# push args
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68/push "Adc"/imm32
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68/push "Abc"/imm32
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# call
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e8/call string_equal/disp32
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# discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
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# call check_ints_equal(EAX, 0, msg)
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# push args
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68/push "F - test_compare_inequal_strings_equal_lengths"/imm32
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68/push 0/imm32/false
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50/push-EAX
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# call
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e8/call check_ints_equal/disp32
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# discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
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c3/return
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