Locate a tile in a row
Before you start this master track
Binary and hexadecimal numbers, memory addresses, register widths, and signed arithmetic.
Master is the entry-background tier for this track. These three introductory x86-64 exercises cover registers, masks, shifts, and flags; completing them does not establish mastery of Assembly.
Guided code reading and debugging. Runnable coding challenges are available in JavaScript, Python, and SQL.
Understand it, then try it.
A left shift moves a bit pattern toward higher bit positions and fills the low positions with zeroes. For an unsigned value that fits, shifting left by three multiplies it by eight. This snippet uses an eight-byte stride, adds a three-byte position within the tile, and copies the offset to EAX.
mov ecx, 7shl ecx, 3add ecx, 3mov eax, ecxx86-64 instruction snippets in Intel/NASM syntax, not complete OS programs. Step from the first instruction through the last in a debugger, then inspect the named registers. eax, ebx, and ecx are 32-bit registers; cl is the low byte of ecx. No console output or system calls are used.
Track the values line by line. Predict the result before running this example in your own editor.