/* Auther:        mrynit
 * Date:        4-22-05
 * Class:        TCSS 372
 * Assign:        ptroplab
 * 
 * System developed on:
 * Ubuntu 7.10
 * gcc version 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)
 * using flag -masm=intel for intel syntax instead of AT&T.
 * Eclipse Platform Version: 3.3.1.1
 * 
 */
 
#include <stdio.h>
 
/* All varieabls here are global so thay can be used in ASM. */
 
/* 'A'  I chose this value so it would be a printable character*/
char c = 65; 
 
/* Max positive value of signed int. */
int i = 2147483647;
double d = 128.128;
 
/* holds value from the registers used for printing*/
int int_holder1;
int int_holder2;
int int_holder3;
int int_holder4;
 
int main(int argc, char* argv[])
{
 
        /* c is char 8 bits. moving a small value into a large or equal 
         * register works fine 
         */
        asm(
                        ".intel_syntax noprefix;"
                        "mov al, c;" /* 8 bit low */
                        "mov ah, c;" /* 8 bit high */
                        "mov ax, c;" /* 16 bit */
                        "mov eax, c;" /* 32 bit */
                        "mov int_holder1, al;"
 
                        /* placed the values in the registers into int variables so the 
                         * register values can be printed to screen*/
                        "mov int_holder2, ah;"
                        "mov int_holder3, ax;"
                        "mov int_holder4, eax;"
        );
 
        printf("the value of c = %d\n", c);
        printf("moved value of i placed into al = %d\n", int_holder1);
        printf("moved value of i placed into ah = %d\n", int_holder2);
        printf("moved value of i placed into ax = %d\n", int_holder3);
        printf("moved value of i placed into eax = %d\n\n", int_holder4);
 
 
        /* moving a large value into a smaller register SHOULD not work.
         * Why do these work? For some reason on my setup(see above) 
         * "autocasting" is on  I don not have to use [size typte] ptr [var]
         * I wonder if running this code in windows would work. 
         */
        asm(
                        "mov al, i;"                        
                        "mov ah, i;"                        
                        "mov ax, i;"                        
                        "mov eax, i;"
 
                        "mov int_holder1, al;"
                        "mov int_holder2, ah;"
                        "mov int_holder3, ax;"
                        "mov int_holder4, eax;"
 
        );
 
        printf("the value of i = %d\n", i);
        printf("moved value of i placed into al = %d\n", int_holder1);
        printf("moved value of i placed into ah = %d\n", int_holder2);
        printf("moved value of i placed into ax = %d\n", int_holder3);
        printf("moved value of i placed into eax = %d\n\n", int_holder4);
 
        /*However if i want to explicitly cast large value to small I can.
         * I have no idea why this works.
         */
        asm(
                        "mov al, byte ptr i;"
                        "mov ah, byte ptr i;"
                        "mov ax, word ptr i;"
                        "mov eax, dword ptr i;"
 
                        "mov int_holder1, al;"
                        "mov int_holder2, ah;"
                        "mov int_holder3, ax;"
                        "mov int_holder4, eax;"
        );
 
        printf("the value of i = %d\n", i);
        printf("Using ptr for cast");
        printf("moved value of i placed into al = %d\n", int_holder1);
        printf("moved value of i placed into ah = %d\n", int_holder2);
        printf("moved value of i placed into ax = %d\n", int_holder3);
        printf("moved value of i placed into eax = %d\n\n", int_holder4);
 
 
        /* Again moving large vales into small registers is done by auto 
         * casting.
         */
        asm(                        
                        "mov al, d;"                        
                        "mov ah, d;"                        
                        "mov ax, d;"                        
                        "mov eax, d;"
 
                        "mov int_holder1, al;"
                        "mov int_holder2, ah;"
                        "mov int_holder3, ax;"
                        "mov int_holder4, eax;"
        );
 
        printf("the value of d = %f\n", d);
        printf("moved value of d placed into al = %d\n", int_holder1);
        printf("moved value of d placed into ah = %d\n", int_holder2);
        printf("moved value of d placed into ax = %d\n", int_holder3);
        printf("moved value of d placed into eax = %d\n\n", int_holder4);
 
        return 0;
}