This code shows how to write in-line assembly in C\C++. I tried it with MVC 6.0, but I'm almost convinced that it'll work with other compilers.
Generaly, the assembly procedure takes a WORD (16 bits \ 2 bytes) and replaces the upper byte with the lower (not special, I know, but a good example of somthing hard to do without ASM).
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No inputs.
Tested on MVC 6, windows XP, Pentium 4 1.80GHz.
Returns some values & their values after upper-lower byte swap.
Also returns the assembly code (prints it to the screen).
No side effects.
| Submitted On | |
| By | OR13 |
| Level | Intermediate |
| User Rating | 5.0 (10 globes from 2 users) |
| Compatibility | C, C++ (general), Microsoft Visual C++ |
| Category | Algorithms |
| World | C / C++ |
| Archive File |
#include <iostream.h>
int SwapLowHigh(int num)
{
int retu;
_asm
{
mov edx,num
xor eax,eax ;//clear eax. why? because later we'll return eax instead of only ax...
mov ax,dx ;//until now it was just prepare. now it beggins
mov dl,al ;//dl acts like 'temp'
mov al,ah ;//swap
mov ah,dl
mov retu,eax ;//return the value in eax (actually in ax, the first word is cleaned)
}
return retu;
}
int main()
{
cout<<"SwapLowHigh(1):\t\t"<<SwapLowHigh(1)<<"\n"; //print for example "SwapLowHigh(16): 4096"
cout<<"SwapLowHigh(2):\t\t"<<SwapLowHigh(2)<<"\n";
cout<<"SwapLowHigh(4):\t\t"<<SwapLowHigh(4)<<"\n";
cout<<"SwapLowHigh(8):\t\t"<<SwapLowHigh(8)<<"\n";
cout<<"SwapLowHigh(16):\t"<<SwapLowHigh(16)<<"\n";
cout<<"SwapLowHigh(32):\t"<<SwapLowHigh(32)<<"\n";
cout<<"SwapLowHigh(64):\t"<<SwapLowHigh(64)<<"\n";
cout<<"SwapLowHigh(128):\t"<<SwapLowHigh(128)<<"\n";
cout<<"SwapLowHigh(256):\t"<<SwapLowHigh(256)<<"\n";
cout<<"SwapLowHigh(512):\t"<<SwapLowHigh(512)<<"\n";
cout<<"SwapLowHigh(1024):\t"<<SwapLowHigh(1024)<<"\n";
cout<<"SwapLowHigh(2048):\t"<<SwapLowHigh(2048)<<"\n";
cout<<"SwapLowHigh(4096):\t"<<SwapLowHigh(4096)<<"\n";
cout<<"SwapLowHigh(8192):\t"<<SwapLowHigh(8192)<<"\n";
cout<<"SwapLowHigh(16384):\t"<<SwapLowHigh(16384)<<"\n";
cout<<"SwapLowHigh(32768):\t"<<SwapLowHigh(32768)<<"\n\n\n";
cout<<"Code:\n\n"; //print the assembly code
cout<<"int SwapLowHigh(int num)\n{\n\tint retu;\n\t_asm\n\t{\n";
cout<<"\t\tmov edx,num\n\t\txor eax,eax\t\t;//later returned instead of ax.\n";
cout<<"\t\tmov ax,dx\t\t;//until now it was just prepare.\n";
cout<<"\n\t\tmov dl,al\t\t;//dl acts like 'temp'\n\t\tmov al,ah\t\t;//swap\n";
cout<<"\t\tmov ah,dl\n\n\t\tmov retu,eax\t\t;//eax is integer, ax is word\n";
cout<<"\t}\n\treturn retu;\n}\n\n";
return 0;
}