How to do unsigned saturating addition in C?

Asked 2008-09-23T14:12:50.777

52

What is the best (cleanest, most efficient) way to write saturating addition in C?

The function or macro should add two unsigned inputs (need both 16- and 32-bit versions) and return all-bits-one (0xFFFF or 0xFFFFFFFF) if the sum overflows.

Target is x86 and ARM using gcc (4.1.2) and Visual Studio (for simulation only, so a fallback implementation is OK there).

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1 Answer

17

In IA32 without conditional jumps:

uint32_t sadd32(uint32_t a, uint32_t b)
{
#if defined IA32
  __asm
  {
    mov eax,a
    xor edx,edx
    add eax,b
    setnc dl
    dec edx
    or eax,edx
  }
#elif defined ARM
  // ARM code
#else
  // non-IA32/ARM way, copy from above
#endif
}

answered 2008-09-23T14:31:08.627

How to do unsigned saturating addition in C?

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