branch problems

[habran]

Hi Japheth
can you please explain why is 

.if ( < eax) compiled to:
0000000140054BA7  cmp         dword ptr ,eax
0000000140054BAA jae         0000000140055017

and 
.if (.AXLINEDATA.nLineBreak < eax)compiled to:
0000000140054BA7  cmp         dword ptr ,eax
0000000140054BAA jge         0000000140055017

I have bug in my program because of it

regards

[habran]

jae is good
jge is bad

[japheth]

> can you please explain why is

No - you haven't supplied the declaration of AXLINEDATA. But I guess the difference is due to how member nLineBreak is defined - signed or unsigned.

[habran]

AXLINEDATA struct
next               INT_PTR ?
prev               INT_PTR ?
wpLine       INT_PTR ?
nLineLen      SDWORD ?
nLineBreak    BYTE ?
nLineFlags     BYTE ?
nReserved    WORD ?
nLineWidth    SDWORD ?
nSelStart      SDWORD ?
nSelEnd      SDWORD ?
AXLINEDATA ends

[habran]

anyway
why is   considered as signed?
and .AXLINEDATA.nLineBreak as usigned

[habran]

sorry it is not .AXLINEDATA.nLineBreak in question
but .AXLINEDATA.nLineWidth
however it is translated in to :
0000000140054BA7  cmp         dword ptr ,eax
0000000140054BAA  jge         0000000140055017

[japheth]

> however it is translated in to
>: 0000000140054BA7 cmp dword ptr ,eax
>  0000000140054BAA jge 0000000140055017

I don't see the problem. "jae" is generated if unsigned values are compared, and "jge" is generated if signed values are compared. Since nLineWidth is signed, all looks ok. Am I missing something?

[habran]

yes, have look again I tried it again and still the same resoult
     mov eax, DWORD PTR dwMaxWidth
    .if (.AXLINEDATA.nLineWidth < eax)

0000000140054BA4  mov         eax,dword ptr 
0000000140054BA7  cmp         dword ptr ,eax
0000000140054BAA  jge         0000000140054F40

I tried with mov eax, SDWORD PTR dwMaxWidth
with .if (SDWORD PTR.AXLINEDATA.nLineWidth < SDWORD PTR eax)

and still the same

only
.if ( < eax) is compiled to:
0000000140054BA7  cmp         dword ptr ,eax
0000000140054BAA  jae         0000000140055017

[habran]

my question is why is .if ( < eax)
compiled to jae
how did compiler make decision that it is jae and not jge when there is nothing telling it about SIGNED or NOT?

[japheth]

I'd say you are confused. If you want an unsigned comparison, you'll have to write:

.if DWORD PTR .AXLINEDATA.nLineWidth < eax

if there's no typecast ("DWORD PTR"), the comparison will be signed.

Just write a 32-bit version and test it with Masm, you'll see that it behaves equally.

[habran]

you were right, with:
  mov eax, DWORD PTR dwMaxWidth
    .if (DWORD PTR.AXLINEDATA.nLineWidth < eax)
I have finally got it
0000000140054BA7  cmp         dword ptr ,eax
0000000140054BAA  jae         0000000140054F40

however, why SDWORD PTR doesn't give the same result?

[habran]

IMO it would be more logical that SDWORD PTR create signed and DWORD PTR unsigned
however, thank you Japheth for solving the mistery

[japheth]

> IMO it would be more logical that SDWORD PTR create signed and DWORD PTR unsigned

Yes …. that's what they actually DO!

>  however, thank you Japheth for solving the mistery

You're welcome! However, there's no mystery .  take a break, and then review the Intel manuals, JCC instruction!

[habran]

sorry to bother you
I don't know why I thought that jge is unsigned and jae unsigned
actually, I know: my IGNORANCE
I rarely use  cmp because I like C stile .if