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Index > Macroinstructions > FASMG: question about lengthof operator

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fabbel



Joined: 30 Oct 2012
Posts: 83
fabbel 27 Mar 2024, 14:42
Hi Tomasz,

quick / small question reg. FASMG lengthof operator :
if I do e.g.
Code:
LEN = lengthof 0x0FF
    

-> i get LEN = 2, despite value obviously being 1-byte only
.. and similar behavior - i.e. byte lentgh +1 - for any value with sign bit set: 0x80, 0x9000, ...


Is this this intended / on purpose ? ... so need to reimplement some 'byte length' operator then ?
Post 27 Mar 2024, 14:42
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Tomasz Grysztar



Joined: 16 Jun 2003
Posts: 8340
Location: Kraków, Poland
Tomasz Grysztar 27 Mar 2024, 15:26
The LENGHTOF is only defined for string values, and when you use it with another kind of value, it is implicitly converted to string first, so "lengthof 0xFF" is the same as "lengthof string 0xFF".
If you test this:
Code:
db string 0xFF    
you can see that the value is converted into a 2-byte string. That's because fasmg always treats the numbers as sign-extended, little endian with arbitrary length (so it's the highest bit of the last byte that needs to be equal to the sign):
Code:
db string -1        ; 1 byte
db string 0xFF      ; 2 bytes
db string -8000h    ; 2 bytes
db string 8000h     ; 3 bytes    
Also if you convert a string back into a number, it is interpreted as a sign-extended value.
Post 27 Mar 2024, 15:26
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