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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: How do I write directly to a memory address?
Date: Fri, 4 Feb 2011 01:24:01 -0800 (PST)
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Date: 2011-02-04T01:24:01-08:00
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Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:
> Syntax Issues wrote on comp.lang.ada:
>> I am planning to start learning lower-level programming with ada,
>> however, I was unable to find a solid tutorial on writing directly to
>> a memory address or interfacing with assembly. Does anyone know where
>> I can find a reference to some tutorials/information? Below is an
>> example of code I would like to be able to implement.
>
>> ...
>> unsigned int print(char *message, unsigned int line)
>> {
>> =A0 =A0 =A0 =A0 char *vidmem =3D (char *) 0xb8000;
>> =A0 =A0 =A0 =A0 unsigned int i=3D 0;
>>
>> =A0 =A0 =A0 =A0 i=3D(line*80*2);
>>
>> =A0 =A0 =A0 =A0 while(*message!=3D0) // 24h

Did I mention that *every* time I look at C code I see a bug?
Sometimes, looking twice at the same code reveals two bugs! Here you
do not check that message !=3D NULL; the condition should be:

           while (message && *message !=3D 0)

>> =A0 =A0 =A0 =A0 {
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 vidmem[i]=3D *message;
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 *message++;
>
> *Every* time I look at C code, I see a bug.
> I think this is a bug; it should read "message++" since you want to
> increment the pointer, not the pointed-to character.
>
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 i++;
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 vidmem[i]=3D 0x7;
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 i++;
>> =A0 =A0 =A0 =A0 };
>>
>> =A0 =A0 =A0 =A0 return(1);};

--
Ludovic Brenta.