Inline Assembly Code

• Higher-level languages such as C and C++ run on nearly all architectures and yield higher productivity when writing and maintaining code.
• GNU Compiler Collection permits programmers to add architecture-dependent assembly language instructions to their programs. For example, programs using x86 instructions cannot be compiled on Power PC computers.
• Inline assembly statements permit you to access hardware directly and can also yield faster code.
• An asm instruction allows you to insert assembly instructions into C and C++ programs. For example, this instruction

  asm ("fsin" :"=t" (answer) : "0" (angle));
  

  is an x86-specific way of coding this C statement:

  answer = sin (angle);
  

• The expression sin (angle) is usually implemented as a function call into the math library, but if you specify the $-O1$ or higher optimization flag, GCC is smart enough to replace the function call with a single fsin assembly instruction.