Inline asm for ARM

Andrew Haley
Wed Jun 16 16:37:00 GMT 2010

On 06/16/2010 01:15 PM, Andrew Haley wrote:
> On 06/16/2010 11:23 AM, Pavel Pavlov wrote:
>> I spent hours to get it working properly, but it seems that I can't find a way to do it properly.
>> In arm 5te, there is an instruction SMLALBB
>> SMLALBB RdLo, RdHi, Rm, Rs
>> Multiples bottom 16 bits of Rm by bottom 16 bits of Rs and adds 32 bit result to 64 bit integer represented by a pair of register RdLo, RdHi.
>> So, I tried everything I can and it seems that I can't get it working.
>> The closest try was:
>> static __inline void smlalbb(int * lo, int * hi, int x, int y)
>> {
>> 	__asm__ __volatile__("smlalbb %0, %1, %2, %3" : "=&r"(lo), "=&r"(hi) : "r"(x), "r"(y), "0"(lo), "1"(hi));
>> }
>> It seem to produce correct result, but that worked only for simple test function, if I chained calls to this smlalbb function the results weren't correct anymore.
>> The correct way would probably have to use (*lo) and (*hi) as part of register lists, but in that case it adds too many useless loads and stores (instead of translating directly to a single asm instruction it would generate like 8-10 instructions).
> I think it should be

Sorry, my mistake.

inline uint64_t smlalbb(uint64_t acc, unsigned int lo, unsigned int hi)
    uint64_t ll;
      unsigned int l;
      unsigned int h;
    } s;
  } retval;

  retval.ll = acc;

  __asm__("smlalbb %0, %1, %2, %3"
	  : "+r"(retval.s.l), "+r"(retval.s.h)
	  : "r"(lo), "r"(hi));

  return retval.ll;


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