Intel® 64 and IA-32 Architectures Optimization Reference Manual

GENERAL OPTIMIZATION GUIDELINES— An iterative approach using the instruction with largest data granularity,where the overhead for SIMD feature detection, iteration overhead, andprolog/epilogue for alignment control can be minimized. The trade-offbetween these approaches may depend on the microarchitecture.An example of MEMSET() implemented using stosd for arbitrary counter valuewith the destination address aligned to doubleword boundary in 32-bit mode isshown in Example 3-44.• When N is larger than half the size of the last level cache, using 16-bytegranularity streaming stores with prolog/epilog for address alignment will likelybe more efficient, if the destination addresses will not be referenced immediatelyafterwards.Example 3-44. REP STOSD with Arbitrary Count Size and 4-Byte-Aligned DestinationA ‘C’ example of Memset()Equivalent Implementation Using REP STOSDvoid memset(void *dst,int c,size_t size){char *d = (char *)dst;size_t i;for (i=0;i