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I'm trying to write a simple code in assembly and I'm having troubles when comparing two values using cmp. I want to jump to a certain point if my value is not between 65 and 90.

 cmp $65, (%ebx) jl looping cmp $90, (%ebx) jg check_minusculas

Running gdb I have that %ebx value is 0x80490f9 and using:

x /1db 0x80490f9

I get that (%ebx) is 77. However, the program jumps to check_minusculas when obviously 77<90.
What am I missing here?

Thanks!

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1 Answer 1

Reset to default
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Your problem is that you forgot to use a size specifier and it defaults to long while you apparently want to use byte. Solution: use cmpb.

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2 Comments

This worked, thanks! But what is happening "behind the scenes"? If it's a byte and defaults to long, doesn't it fill the other bytes as a 0?
No, it fetches the following 3 bytes as well from memory, whatever they may be.

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