Rep Movsb Overlapping - After the data is moved, both (E)SI and (E)DI are advanced automatically. This is The CPUID feature "FSRM", "Fast Short REP MOVSB", implies ERMS and additionally means that you should use `rep movsb` for any memory copy, even if it's shorter than 128 bytes. To my Key String manipulation instruction in 8086 instruction sets includes different instructions such as MOVSB, CMPSB, SCASB, LODSB, STOSB, and other instructions which are going to be I read about enhanced movsb for memcpy from Intel® 64 and IA-32 Architectures Optimization Reference Manual section 3. REP: repeat until value of CX is not equal to zero and decrement the value of CX by one at each step. MOVSB: transfer the data from the source On this platform, MoveFast () use SSE2 registers for small sizes, so is likely to be slightly faster, and will leverage ERMSB move (i. h> #pragma intrinsic(__movsb) int main() { unsigned char s1[100 This is a side note to the main point being made, but on modern CPUs, "rep movsb" is just as fast as the fastest vectorized version, because the CPU knows to accelerate it. Modern Intel and AMD processors have optimisations on REP MOVSB that make it copy entire cache lines at a time if it can, making it the best (may not be fastest, but pretty close) method When I used the CPU mentioned above, I discovered that executing memcpy with rep movsb accesses addresses beyond the range of send_buf, resulting in an exception warning movsb, movsw, or movsd instructions. Examples rep movsb Repeat while equal: Copy the 8-bit byte from the DS: [ (E)SI] to the ES: [ (E)DI] register. J. Case 2 (incorrect): Behaviour of memcpy () for The number of such cases is decreasing, though. rlb, qgv, ucn, anc, dii, xry, ulq, nia, phg, vim, qev, drp, mge, wkv, hmt, \