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POHow would I append a 64-bit Big-Endian int in ASM?
 

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  1. POHow would I append a 64-bit Big-Endian int in ASM?
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    <p>I am new to Assembly, but not new to programming and how it works in general. Because I know quite a few languages already, I decided to make my first ASM program calculate the SHA-1 hash of input files. I already have many of the separate parts worked out, but there are two parts I am having trouble with; one I will ask for help with here.</p> <p>Basically, I am confused over the concepts of Big and Little endian numbers and how to represent them in ASM. To quote from the SHA-1 Psuedocode:</p> <pre><code>append length of message (before pre-processing), in bits, as 64-bit big-endian integer </code></pre> <p>The only things that come to mind is to, for example represent the number 1 as:</p> <pre><code>[63 0's]1 </code></pre> <p>Or</p> <pre><code>1[63 0's] </code></pre> <p>Or</p> <pre><code>[31 0's] 1 [32 0's] </code></pre> <p>Basically my thought so far is basically:</p> <pre><code>mov eax, message ;Move message to be hashed into eax shl eax, 64 ;Shift message over enough bits to store 64-bits or eax, msglen ;Adds message length to the very end of message </code></pre> <p>This is most likely wrong, as this all uses 32-bit registers therefore shifting left 64-bits would create a huge overflow but that is just another problem I have yet to work out.</p> <p>I think I've gone way off track, but basically my question is is the above code a correct way to append a big-endian integer? Or do I have it backwards, or am I just completely off on everything, etc. Not sure if this makes sense, too tired.</p>
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    1. USKen White
    1. USozdrgnaDiies
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    1. COFirst you need to specify which processor. On many processors, you won't have to do anything special.
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      1. USAShelly
    2. COhave you implemented it in a language you know, C or something like that? Start there then, write that it simple steps then convert that to asm.
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      1. USold_timer
    3. COThat is also a pretty basic thing I have looked over. I will start this tomorrow since I know I can do this in C fairly easily. Thanks for the tip.
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      1. POHow would I append a 64-bit Big-Endian int in ASM?
      1. USozdrgnaDiies
 

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