diff options
Diffstat (limited to 'subx/052kernel-string-equal.subx')
| -rw-r--r-- | subx/052kernel-string-equal.subx | 54 |
1 files changed, 31 insertions, 23 deletions
diff --git a/subx/052kernel-string-equal.subx b/subx/052kernel-string-equal.subx index b61c3303..840b4460 100644 --- a/subx/052kernel-string-equal.subx +++ b/subx/052kernel-string-equal.subx @@ -30,19 +30,26 @@ # reason for the name: the only place we should have null-terminated ascii strings is from commandline args kernel-string-equal?: # s : null-terminated ascii string, benchmark : length-prefixed ascii string -> EAX : boolean # pseudocode: - # initialize n = b->length - # initialize s1 = s - # initialize s2 = b->data + # n = benchmark->length + # s1 = s + # s2 = benchmark->data # i = 0 - # for (i = 0; i < n; ++n) + # while (i < n) # c1 = *s1 # c2 = *s2 - # if c1 == 0 - # return false - # if c1 != c2 - # return false + # if (c1 == 0) return false + # if (c1 != c2) return false + # ++s1, ++s2, ++i # return *s1 == 0 # + # registers: + # i: ECX + # n: EDX + # s1: EDI + # s2: ESI + # c1: EAX + # c2: EBX + # # . prolog 55/push-EBP 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP @@ -52,24 +59,25 @@ kernel-string-equal?: # s : null-terminated ascii string, benchmark : length-pr 53/push-EBX 56/push-ESI 57/push-EDI - # initialize s into EDI + # s1/EDI = s 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 7/r32/EDI 8/disp8 . # copy *(EBP+8) to EDI - # initialize benchmark length n into EDX + # n/EDX = benchmark->length 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 2/r32/EDX 0xc/disp8 . # copy *(EBP+12) to EDX 8b/copy 0/mod/indirect 2/rm32/EDX . . . 2/r32/EDX . . # copy *EDX to EDX - # initialize benchmark data into ESI + # s2/ESI = benchmark->data 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 6/r32/ESI 0xc/disp8 . # copy *(EBP+12) to ESI 81 0/subop/add 3/mod/direct 6/rm32/ESI . . . . . 4/imm32 # add to ESI - # initialize loop counter i into ECX + # i/ECX = c1/EAX = c2/EBX = 0 b9/copy-to-ECX 0/imm32/exit - # while (i/ECX < n/EDX) + b8/copy-to-EAX 0/imm32 + bb/copy-to-EBX 0/imm32 $kernel-string-equal?:loop: + # if (i >= n) break 39/compare 3/mod/direct 1/rm32/ECX . . . 2/r32/EDX . . # compare ECX with EDX - 74/jump-if-equal $kernel-string-equal?:break/disp8 - # c1/EAX, c2/EBX = *s, *benchmark - b8/copy-to-EAX 0/imm32 + 7d/jump-if-greater-or-equal $kernel-string-equal?:break/disp8 + # c1 = *s1 8a/copy 0/mod/indirect 7/rm32/EDI . . . 0/r32/EAX . . # copy byte at *EDI to lower byte of EAX - bb/copy-to-EBX 0/imm32 + # c2 = *s2 8a/copy 0/mod/indirect 6/rm32/ESI . . . 3/r32/EBX . . # copy byte at *ESI to lower byte of EBX # if (c1 == 0) return false 3d/compare-EAX 0/imm32 @@ -77,22 +85,21 @@ $kernel-string-equal?:loop: # if (c1 != c2) return false 39/compare 3/mod/direct 0/rm32/EAX . . . 3/r32/EBX . . # compare EAX with EBX 75/jump-if-not-equal $kernel-string-equal?:false/disp8 - # ++s1, ++s2, ++i + # ++i 41/inc-ECX - 46/inc-ESI + # ++s1 47/inc-EDI - # end while + # ++s2 + 46/inc-ESI eb/jump $kernel-string-equal?:loop/disp8 $kernel-string-equal?:break: - # if (*s/EDI == 0) return true - b8/copy-to-EAX 0/imm32 + # return *s1 == 0 8a/copy 0/mod/indirect 7/rm32/EDI . . . 0/r32/EAX . . # copy byte at *EDI to lower byte of EAX 3d/compare-EAX 0/imm32 75/jump-if-not-equal $kernel-string-equal?:false/disp8 $kernel-string-equal?:true: b8/copy-to-EAX 1/imm32 eb/jump $kernel-string-equal?:end/disp8 - # return false $kernel-string-equal?:false: b8/copy-to-EAX 0/imm32 $kernel-string-equal?:end: @@ -253,6 +260,7 @@ test-compare-kernel-string-with-longer-array: Null-kernel-string: 00/null + _test-Abc-kernel-string: 41/A 62/b 63/c 00/null |