for loop for loop rep movsb gcc clang ------------------------------------------------------------------------------- 128 octets 22,654 MB/s 32,076 MB/s * 15,417 MB/s 128 octets 22,610 MB/s 32,076 MB/s * 15,417 MB/s 192 octets 25,198 MB/s 29,422 MB/s * 17,267 MB/s 192 octets 25,162 MB/s 33,262 MB/s * 22,110 MB/s 256 octets 26,670 MB/s 47,235 MB/s * 25,348 MB/s 320 octets 27,664 MB/s 49,645 MB/s * 30,449 MB/s 384 octets 28,360 MB/s 36,633 MB/s 37,765 MB/s * 448 octets 28,852 MB/s 53,601 MB/s * 38,840 MB/s 512 octets 23,237 MB/s 52,214 MB/s * 42,391 MB/s 576 octets 29,587 MB/s 55,310 MB/s * 46,318 MB/s 704 octets 30,088 MB/s 57,081 MB/s * 52,285 MB/s 832 octets 30,466 MB/s 58,251 MB/s * 57,235 MB/s 1,024 octets 30,830 MB/s 59,536 MB/s 64,106 MB/s * 1,216 octets 27,783 MB/s 60,425 MB/s 69,970 MB/s * 1,536 octets 28,771 MB/s 61,093 MB/s 76,930 MB/s * 1,856 octets 29,368 MB/s 61,794 MB/s 85,111 MB/s * 2,240 octets 29,806 MB/s 62,378 MB/s 88,148 MB/s * 2,752 octets 30,273 MB/s 60,425 MB/s 94,241 MB/s * 3,328 octets 30,541 MB/s 61,095 MB/s 89,152 MB/s * 3,904 octets 28,909 MB/s 58,375 MB/s 90,795 MB/s * 4,736 octets 29,366 MB/s 61,721 MB/s 95,476 MB/s * 5,632 octets 30,307 MB/s 62,662 MB/s 104,090 MB/s * 6,848 octets 30,821 MB/s 62,555 MB/s 105,897 MB/s * 8,256 octets 30,575 MB/s 62,336 MB/s 110,926 MB/s * 10,048 octets 31,359 MB/s 61,834 MB/s 113,766 MB/s * 12,032 octets 31,582 MB/s 63,510 MB/s 115,530 MB/s * 15,040 octets 31,639 MB/s 58,637 MB/s 114,290 MB/s * 18,048 octets 31,616 MB/s 48,569 MB/s 75,210 MB/s * 22,016 octets 31,681 MB/s 40,430 MB/s 50,099 MB/s * 27,008 octets 31,625 MB/s 40,961 MB/s 50,967 MB/s * 33,024 octets 31,507 MB/s 40,619 MB/s 52,680 MB/s * 39,040 octets 31,575 MB/s 40,615 MB/s 52,918 MB/s * 47,040 octets 31,519 MB/s 40,568 MB/s 53,196 MB/s * 56,000 octets 31,561 MB/s 40,655 MB/s 53,302 MB/s * 68,032 octets 31,536 MB/s 39,159 MB/s 53,806 MB/s * 82,048 octets 31,581 MB/s 40,542 MB/s 53,170 MB/s * 100,032 octets 31,461 MB/s 37,401 MB/s 54,235 MB/s * 120,000 octets 31,301 MB/s 37,181 MB/s 50,280 MB/s * 150,016 octets 29,712 MB/s 34,169 MB/s 47,412 MB/s * 180,032 octets 27,817 MB/s 28,274 MB/s 45,291 MB/s * 220,032 octets 26,036 MB/s 26,443 MB/s 40,960 MB/s * 270,016 octets 25,215 MB/s 25,614 MB/s 37,296 MB/s * 330,048 octets 24,938 MB/s 25,633 MB/s 35,541 MB/s * 390,016 octets 24,858 MB/s 26,151 MB/s 34,483 MB/s * 470,016 octets 24,820 MB/s 25,428 MB/s 32,863 MB/s * 560,000 octets 24,664 MB/s 25,583 MB/s 33,046 MB/s * 680,000 octets 24,717 MB/s 25,381 MB/s 32,696 MB/s * 820,032 octets 24,834 MB/s 25,598 MB/s 32,637 MB/s * 1,000,000 octets 25,081 MB/s 25,696 MB/s 32,753 MB/s * 1,200,000 octets 24,591 MB/s 25,600 MB/s 33,028 MB/s * 1,500,032 octets 24,654 MB/s 25,386 MB/s 32,816 MB/s * 1,800,000 octets 24,698 MB/s 25,553 MB/s 32,798 MB/s * 2,200,000 octets 24,401 MB/s 24,965 MB/s 32,425 MB/s * 2,700,032 octets 23,786 MB/s 24,714 MB/s 32,388 MB/s * 3,300,032 octets 23,117 MB/s 23,721 MB/s 29,886 MB/s * 3,900,032 octets 21,407 MB/s 21,845 MB/s 28,940 MB/s * 4,700,032 octets 18,672 MB/s 19,427 MB/s 24,755 MB/s * 5,600,000 octets 16,203 MB/s 16,455 MB/s 21,453 MB/s * 6,800,000 octets 13,453 MB/s 13,564 MB/s 16,698 MB/s * 8,200,000 octets 12,315 MB/s 12,578 MB/s 14,405 MB/s * 10,000,000 octets 11,513 MB/s 11,684 MB/s 12,873 MB/s * 12,000,000 octets 10,566 MB/s 10,691 MB/s 11,514 MB/s * 15,000,000 octets 9,565 MB/s 9,693 MB/s 10,690 MB/s * 18,000,000 octets 9,234 MB/s 9,446 MB/s 10,260 MB/s * 22,000,000 octets 9,187 MB/s 9,298 MB/s 10,245 MB/s * 27,000,000 octets 9,083 MB/s 9,139 MB/s 10,289 MB/s * 33,000,000 octets 8,927 MB/s 9,049 MB/s 9,196 MB/s * 39,000,000 octets 8,888 MB/s 8,990 MB/s 10,215 MB/s * 47,000,000 octets 8,846 MB/s 8,917 MB/s 10,229 MB/s * 56,000,000 octets 8,835 MB/s 8,914 MB/s 10,231 MB/s * 68,000,000 octets 8,722 MB/s 8,888 MB/s 10,195 MB/s * 82,000,000 octets 8,766 MB/s 8,806 MB/s 10,175 MB/s * '*' marks the fastest. $ sysctl -n machdep.cpu.brand_string Intel(R) Core(TM) i7-8700B CPU @ 3.20GHz