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The C Users' Group Library 1994 August
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wc-cdrom-cusersgrouplibrary-1994-08.iso
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v_07_08
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v7n8048a.txt
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1989-09-29
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811b
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38 lines
*****Listing 1*****
/* These are determined from the debug information */
#define AND_INSTRUCTION_OFFSET 0x10
#define OR_INSTRUCTION_OFFSET 0x15
set_plot_type(type)
{
unsigned char *pc;
void draw_function();
/* The function you want to modify */
pc = (void *) draw_function;
switch(type)
{
case XOR:
/* Put NOPS for the masking operation */
*(pc + AND_INSTRUCTION OFFSET) = 0x90; /* NOP */
*(pc + AND_INSTRUCITON OFFSET + 1) = 0X90;
*(pc + OR_INSTRUCTION_OFFSET) = 0x03; /* XOR */
break;
case OVERWRITE:
*(pc + AND_INSTRUCTION_OFFSET) = 0x02; /* AND */
*(pc + AND_INSTRUCITON_OFFSET + 1) = 0x00
/* Register */
*(pc + OR_INSTRUCTION_OFFSET) = 0x08; /* OR */
break;
}
return;
{
*********