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