Message-ID: <36791F45.28CC128@gmx.net> Date: Thu, 17 Dec 1998 16:12:05 +0100 From: Christian Hofrichter X-Mailer: Mozilla 4.5 [de]C-CCK-MCD QXW03201 (Win95; I) X-Accept-Language: de,en MIME-Version: 1.0 To: djgpp AT delorie DOT com Subject: problem with random-functions Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit Reply-To: djgpp AT delorie DOT com I have problem with one of my funtions that usually works fine but crashes with a general protection-fault evertime when I call the random-function before. The strange think is, that if I use a loop and put the random-function in it behind my function it works, but if I try to execute it before I get this general protection-fault. My function changes the ds-register and es-registers because it uses "movsl" to copy memory-blocks. So could anyone tell me if the random function changes something which causes the crash of my program ?
PS: What my function does is to try to copy an image to the vesa framebuffer.

void prot_putsprite(unsigned short X1,unsigned short Y1,void *image)
{
unsigned long address;
unsigned short heigth,width,Y=0;

width=*(unsigned short *)image;
heigth=*(unsigned short *)((unsigned char *)image+2);
(unsigned char *)image+=4; /* update pointer so that it points to the
                                               image-information*/
address=Y1*infomode.BytesPerScanline+X1;
asm("cld");/*clear direction flag so that esi and edi are increased*/
do
{
asm("pushb %ds");/*save data-segment*/
asm("movw %0,%%es":
                   :"r"((unsigned short) vesa_framebuffer) );/*selector for framebuffer*/
asm("movl %0,%%edi" :
                     :"r"(address) ); /*address in framebuffer*/
asm("movl %0,%%esi":
                    :"r"(image) ); /*pointer to image*/
asm("movw %0,%%cx" :
                     :"r"(width) ); /*count of bytes to move*/
asm("movw %0,%%ds":
                   :"r"(program-selector) ); /*same as _my_ds() */
asm("movb %cl,%bl ");/* get the number of bytes which aren't completely
                                         divisible by 4*/
asm("shr   $2,%ecx ");/* calculate count of dword-movement*/
asm("and   $3,%bl ");
asm("rep\n\t"
            "movsl":
                   :
                   :"%ecx","%esi","%edi"); /* move 4-bytes at one time*/
asm("movb %bl,%cl");
asm("rep\n\t"
            "movsb":
                   :
                   :"%ecx","%esi","%edi");/*move the bytes which aren't completely
                                                       divisible by 4*/
asm("popb %ds");/*restore data-segment*/
(unsigned char *)image+=width;/* update pointer*/
address+=infomode.BytesPerScanline;/* update address in framebuffer*/
Y++;
}while(Y<=heigth);

}

PPS: I have written it in assembler because so I can move 4 bytes at one time without making a conditionel jump and reloading all needed registers if the width of the image isn't completely divisible by 4.
PPPS: Propably this discription won't help you much.