QuestionQuestion

PART I
1. Implement the memset function using inline assembly. The memset function copies “value” starting at the destination address and ending at destination address + nCount – 1. It is used to set a block of memory to a specific value, often times initializing a memory block with a value of zero.

memset( void *destination, unsigned char value, int nCount). Example: dst = 0x1000, value = 0xA5, nCount = 5
Memory values
Before: 0x1000: 3A 28 A1 BE CA FE DE AD 11 ... After:0x1000: A5A5A5A5A5FEDEAD11...

   Note: the last address to get the “A5” value is 0x1004 which is dst
   (0x1000) + nCount (5) – 1.
Void function() {
   char string[] = “The end is near!”;
   printf(“The message is: %s\n”, string);
// this is 16 bytes + null
__asm {
   mov eax,16
   push eax
   mov eax,0x41
   push eax
   lea eax,string
   push eax
; push the length
; push the value
; push the address of string
       call inline_memset
       add esp,12
       jmp EXIT
    inline_memset:
          ; this is where you write the code to implement the memset
EXIT: }
    printf(“Now the message is: %s\n”, string);
    return;
   } // end function

PART II
1. Implement the memcmp function using inline assembly. The memcmp function compares two byte sequences starting at each source address and ending at each source address + nCount – 1. If they are equal, it returns zero. If source1 has a value less than source2, then it returns -1. If source1 has a value greater than source2, it returns +1.
   
memcmp( void *source1, void *source2, int nCount)

Example:
char source1[] = { 0x05, 0x6F, 0xAA }
char source2A[] = { 0x05, 0x5F, 0xAA } --- return +1 char source2B[] = { 0x05, 0x70, 0xAA } --- return -1

Consider the data as UNSIGNED, i.e. 0xFF > 0x01. Int inline_memcmp(char *s1, char *s2, int length) {
    int resulti;
    __asm{
               ; your code here
}
    return resulti;
   }
   void function() {
    int tmpi;
    char data[] = { 0x00, 0xF2, 0xAB, 0x16, 0x81, 0x53 };
    char dataA[] = { 0x00, 0xF2, 0xAB, 0x16, 0x81, 0x53 };
    char dataB[] = { 0x00, 0xF2, 0xAB, 0x16, 0x81, 0x53 };
    char dataC[] = { 0x00, 0xF2, 0xAB, 0x16, 0x81, 0x53 };
    tmpi = inline_memcmp(data, dataA, 6);
    printf(Result of dataA is: “, tmpi);
    tmpi = inline_memcmp(data, dataB, 6);
    printf(Result of dataB is: “, tmpi);
    tmpi = inline_memcmp(data, dataC, 6);
    printf(Result of dataC is: “, tmpi);
    return;
   } // end function

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#include <stdio.h>

void function()
{
char string[] = "The end is near!"; // this is 16 bytes + null
printf("The message is : %s\n", string);
__asm {
mov eax, 16; push the length
push eax
mov eax, 0x41; push the value
push eax
lea eax, string; push the address of string
push eax
call inline_memset
add esp, 12
jmp EXIT

inline_memset :
; this is where you write the code to implement the memset
push ebp; save ebp
mov ebp, esp; copy SP reference

; save registers that will be used
push ebx
push ecx
push edi

; get arguments to registers
mov edi, [ebp + 8]; pointer to start location
mov ebx, [ebp + 12]; value
mov ecx, [ebp + 16]; length

; loop length times
L1:
mov[edi], bl; write the value
inc edi; increment pointer
loop L1...

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