Negating a QWORD

[dedndave]

i am guessing that would be 4 cycles   :P
maybe a few more if it were in a proc

this one wants to run at 13...

Code Select Expand

Input Value: FFFFFFFF_FFFFFFFF Output Value: 00000000_00000001, No Overflow
13 13 13 13 13
Input Value: 00000000_00000000 Output Value: 00000000_00000000, No Overflow
13 13 13 13 13
Input Value: 00000000_00000001 Output Value: FFFFFFFF_FFFFFFFF, No Overflow
13 13 13 13 13
Input Value: 7FFFFFFF_FFFFFFFF Output Value: 80000000_00000001, No Overflow
13 13 13 13 13
Input Value: 80000000_00000000 Output Value: 80000000_00000000, Overflow
13 13 13 13 13
Input Value: 80000000_00000001 Output Value: 7FFFFFFF_FFFFFFFF, No Overflow
13 13 13 15 14
Pentium 4 Prescott (2005+), MMX, SSE3

if i show cpu first, it runs at 22 ???   :eek
i should make a macro instead of a proc, i guess  :P

[jj2007]

Just for fun :bg

NegQw   PROC    lpInt:LPVOID
; Negate a qword with overflow
; DednDave, 2-2012
   mov edx, [esp+4]
   JJ=1
   if JJ
      neg dword ptr [edx]
      .if Carry?
         not dword ptr [edx+4]
      .endif
   else
      mov eax, [edx+4]
      neg dword ptr [edx]
      not eax
      sbb eax, -1
      mov [edx+4], eax
   endif
   ret 4
NegQw   ENDP

[dedndave]

well.....

we both have work to do   :bg

Code Select Expand

JJ=1:
Input Value: 00000001_00000000 Output Value: 00000001_00000000, No Overflow

JJ=0:
Input Value: 00000001_00000000 Output Value: FFFFFFF1_00000000, No Overflow

should be:
Input Value: 00000001_00000000 Output Value: FFFFFFFF_00000000, No Overflow

[dedndave]

oops - my code works correctly
i missed a line when copy/paste

Code Select Expand

JJ=1:
Input Value: 00000001_00000000 Output Value: 00000001_00000000, No Overflow

JJ=0:
Input Value: 00000001_00000000 Output Value: FFFFFFFF_00000000, No Overflow

should be:
Input Value: 00000001_00000000 Output Value: FFFFFFFF_00000000, No Overflow

[jj2007]

Better?

Code Select Expand

Input Value: FFFFFFFF_FFFFFFFF Output Value: 00000000_00000001, No Overflow
3 3 3 3 3
Input Value: 00000000_00000000 Output Value: 00000000_00000000, No Overflow
4 4 4 4 4
Input Value: 00000000_00000001 Output Value: FFFFFFFF_FFFFFFFF, No Overflow
3 3 3 3 3
Input Value: 7FFFFFFF_FFFFFFFF Output Value: 80000000_00000001, No Overflow
3 3 3 3 3
Input Value: 80000000_00000000 Output Value: 80000000_00000000, Overflow
4 4 4 4 4
Input Value: 80000000_00000001 Output Value: 7FFFFFFF_FFFFFFFF, No Overflow
3 3 3 3 3
Input Value: 00000001_00000000 Output Value: FFFFFFFF_00000000, No Overflow
4 4 4 4 4
Core (2006+), MMX, SSE3

[dedndave]

i like it   :U

i like this even better

Code Select Expand

        mov     eax,[esp+4]
        neg dword ptr [eax]
        jnc     @F

        not dword ptr [eax+4]
        ret     4

@@:     neg dword ptr [eax+4]
        ret     4
returns the address in EAX

[dedndave]

it's small enough - should probably still be a macro   :P

[jj2007]

i like this even better

The test for equality is needed, I am afraid...

[dedndave]

i don't know why you say that   :red

the only way to get to that point in the code is if the low dword is zero

NEG instruction:
If the operand is zero, its sign does not change, although this clears the carry flag
Negating any other value sets the carry flag

it seems to work fine without it

[jj2007]

i don't know why you say that   :red

the only way to get to that point in the code is if the low dword is zero

NEG instruction:
If the operand is zero, its sign does not change, although this clears the carry flag
Negating any other value sets the carry flag

it seems to work fine without it

It does - sorry, my fault :thumbu

[dedndave]

we need some more of these, Jochen
we are off our tea because we haven't done it much, lately - lol

maybe we can revive my personal favorite - qword to ascii   :P

[jj2007]

qword to ascii   :P

qword to ascii, votsat?

Print Str$("%i\t", qword ptr [esi]), Str$("%i\t", 0-qword ptr [esi])

By the way, dq 8000000000000000h is a tricky case. It just refuses to change sign :green2

[dedndave]

there is a trick for that
it works for some applications - not for all
if the overflow flag is set, treat it as an unsigned value   :P