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[BUG/PRB.] VFP 9.0 FIX - LEFTC() FUNCTION
January 2024
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CCB
1. BUG:
In vfp9 (and vfp7, vfp8), the LEFTC(cExpression, nCharacters) function returns cExpression if nCharacters < 0,
now the LEFTC(cExpression, nCharacters) function returns an empty string if nCharacters < 0.
The bug occurs in vfp7, vfp8 and vfp9, it does not occur in vfp6.
There is a test program:
*PROC testleftcfunction
SET STEP OFF
SET ECHO OFF
SET DEBUG OFF
SET ESCAPE OFF
SET TALK OFF
SET SAFETY OFF
?LEFT("abc",-5) && it displays "".
?LEFTC("abc",-5) && it displays "abc" in vfp9 (and vfp7, vfp8), it displays "" in vfpa (and vfp6).
WAIT
RETURN
* END OF PROC TESTLEFTCFUNCTION.
2. CAUSE:
There are some BUGs in the following code.
3. RESOLUTION:
We can write some code to fix the BUG.
Fun5056ee :: ; proc near
push ecx ;0x005056ee : 51
push ebp ;0x005056ef : 55
push esi ;0x005056f0 : 56
push edi ;0x005056f1 : 57
call Fun420d8c ;0x005056f2 : e895b6f1ff
mov esi , eax ;0x005056f7 : 8bf0
lea ebp , dword ptr [ esi + 44 ] ;0x005056f9 : 8d6e2c
push ebp ;0x005056fc : 55
lea edi , dword ptr [ esp + 16 ] ;0x005056fd : 8d7c2410
call Fun420dd3 ;0x00505701 : e8cdb6f1ff
test eax , eax ;0x00505706 : 85c0
jne Label505757 ;0x00505708 : 754d
push ebx ;0x0050570a : 53
mov eax , esi ;0x0050570b : 8bc6
call Fun42371d ;0x0050570d : e80be0f1ff
mov edi , ebp ;0x00505712 : 8bfd
call Fun529a6e ;0x00505714 : e855430200
cmp byte ptr [ ebp + 0 ] , 049h ;0x00505719 : 807d0049
mov bl , 01h ;0x0050571d : b301
jne Label59104d ;0x0050571f : 0f8528b90800
Label505725 ::
mov eax , dword ptr [ esp + 24 ] ;0x00505725 : 8b442418
test eax , eax ;0x00505729 : 85c0
jne Label59107b ;0x0050572b : 0f854ab90800
Label505731 ::
mov ebx , dword ptr [ esi + 56 ] ;0x00505731 : 8b5e38
test ebx , ebx ;0x00505734 : 85db
jl Label4500ab ;0x00505736 : 0f8c6fa9f4ff
mov eax , dword ptr [ esi + 8 ] ;0x0050573c : 8b4608
cmp ebx , eax ;0x0050573f : 3bd8
jg Label50177e ;0x00505741 : 0f8f37c0ffff
Label505747 ::
mov eax , dword ptr [ esp + 16 ] ;0x00505747 : 8b442410
test eax , eax ;0x0050574b : 85c0
mov dword ptr [ esi + 8 ] , ebx ;0x0050574d : 895e08
pop ebx ;0x00505750 : 5b
jne Label5910bd ;0x00505751 : 0f8566b90800
Label505757 ::
pop edi ;0x00505757 : 5f
pop esi ;0x00505758 : 5e
pop ebp ;0x00505759 : 5d
pop ecx ;0x0050575a : 59
ret 04h ;0x0050575b : c20400
Label59107b ::
mov eax , dword ptr [ esi + 56 ] ;0x0059107b : 8b4638
mov ecx , dword ptr [ esi + 8 ] ;0x0059107e : 8b4e08
cmp eax , ecx ;0x00591081 : 3bc1
;
; ----------------------------------------------------
; VFP 9.0 FIX - LEFTC() FUNCTION
; June 2022
; ----------------------------------------------------
; CCB
;
; In vfp9, the LEFTC(cExpression, nCharacters) function returns cExpression if nCharacters < 0,
; now the LEFTC(cExpression, nCharacters) function returns an empty string if nCharacters < 0.
;
; 2022/6/27, by ccb
;
; jnb Label591087 ;0x00591083 : 7302
jnl Label591087 ;0x00591083 : 7302
mov ecx , eax ;0x00591085 : 8bc8
Label591087 ::
mov eax , dword ptr [ Data9370f4 ] ;0x00591087 : a1f4709300
test byte ptr ah , 010h ;0x0059108c : f6c410
je Label5910b3 ;0x0059108f : 7422
xor eax , eax ;0x00591091 : 33c0
test ecx , ecx ;0x00591093 : 85c9
jle Label5910b5 ;0x00591095 : 7e1e
mov edx , dword ptr [ esi + 32 ] ;0x00591097 : 8b5620
mov edx , dword ptr [edx] ;0x0059109a : 8b12
Label59109c ::
movzx edi ,byte ptr [ eax + edx ] ;0x0059109c : 0fb63c10
test byte ptr [ edi + offset Data937120 ] , bl ;0x005910a0 : 849f20719300
je Label5910ad ;0x005910a6 : 7405
add eax , 02h ;0x005910a8 : 83c002
jmp Label5910ae ;0x005910ab : eb01
Label5910ad ::
inc eax ;0x005910ad : 40
Label5910ae ::
dec ecx ;0x005910ae : 49
jne Label59109c ;0x005910af : 75eb
jmp Label5910b5 ;0x005910b1 : eb02
Label5910b3 ::
mov eax , ecx ;0x005910b3 : 8bc1
Label5910b5 ::
mov dword ptr [ esi + 56 ] , eax ;0x005910b5 : 894638
jmp Label505731 ;0x005910b8 : e97446f7ff
4. APPLIES TO:
VFP 7.0.0.9262
VFP 7.0.0.9465 (SP1)
VFP 8.0.0.2521
VFP 8.0.0.3117 (SP1)
VFP 9.0.0.2412
VFP 9.0.0.3504 (SP1)
VFP 9.0.0.4611 (SP2)
VFP 9.0.0.5015 (SP2)
VFP 9.0.0.5411 (SP2)
VFP 9.0.0.5721 (SP2)
VFP 9.0.0.5815 (SP2)
VFP 9.0.0.6303 (SP2)
VFP 9.0.0.6602 (SP2)
VFP 9.0.0.7423 (SP2)
The bug has been fixed in VFP Advanced.
5. REFERENCE WEBSITES:
1, baiyujia.com:
http://www.baiyujia.com
6. OTHER:
For reference only, there is no guarantees.
Any questions or suggestions, please send me an email at ccb2000@163.com.
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