How do faster two Cmp?

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Roman

Joined: 21 Apr 2012
Posts: 2019

Roman 08 Jan 2024, 09:41

Fasmw 1.73
How do this in three commands?

Code:

Cmp Al, "0"
Jb @f
Cmp Al, "9"
Ja @f
Do some code
@@:

08 Jan 2024, 09:41

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20759
Location: In your JS exploiting you and your system

revolution 08 Jan 2024, 10:10

Code:

sub al,'0'
cmp al,9
ja .out_of_range
; do my thing
.out_of_range:

08 Jan 2024, 10:10

MatQuasar

Joined: 25 Oct 2023
Posts: 105

MatQuasar 08 Jan 2024, 10:33

Try:

Code:

  mov    eax, "1"
  xor    al, 0x30
  cmp    al, 9
  ja     quit

08 Jan 2024, 10:33

Roman

Joined: 21 Apr 2012
Posts: 2019

Roman 08 Jan 2024, 10:39

Thanks.
Both variants work fine.
I tested.

08 Jan 2024, 10:39

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20759
Location: In your JS exploiting you and your system

revolution 08 Jan 2024, 11:02

It is a generic range inclusion test.

Code:

range_begin     =  '0'
range_end       =  '9'

        sub     al,range_begin
        cmp     al,range_end - range_begin
        ja      .out_of_range
        ; do the thing
    .out_of_range:

And it also works for negative ranges (an exclusion test) that wraps around from the beginning to the end

Code:

range_begin     =  '9'
range_end       =  '0'

        sub     al,range_begin
        cmp     al,range_end - range_begin
        ja      .out_of_range
        ; do the thing
    .out_of_range:

08 Jan 2024, 11:02

Picnic

Joined: 05 May 2007
Posts: 1439
Location: Piraeus, Greece

Picnic 09 Jan 2024, 12:10

How about:

Code:


    lea ecx, [eax-'0']
    cmp ecx, 10
    jc _isdigit

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09 Jan 2024, 12:10

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20759
Location: In your JS exploiting you and your system

revolution 09 Jan 2024, 14:31

Using the full eax value might be a problem if the top 24 bits are not well defined. But you can change it to this:

Code:

    lea ecx, [eax-'0']
    cmp cl, 10
    jc _isdigit

09 Jan 2024, 14:31

Roman

Joined: 21 Apr 2012
Posts: 2019

Roman 09 Jan 2024, 14:57

lea ecx, [eax-'0'] not faster than sub AL,"0"
And sub AL,"0" less bytes

lea ecx, [eax-'0'] 3 bytes

sub AL,"0" 2 bytes

09 Jan 2024, 14:57

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