Tested on a Intel Core 2 Duo 2.39 GHz chip in an Apple Mac Book (late 2008 model).

Q_rsqrt_test_out.txt

cmiller-laptop% clang rsqrt_test.c
cmiller-laptop% ./a.out
Q_rsqrt: 4
Q_rsqrt result: 0.499154	Avg: 555
fsqrt   result: 0.500000	Avg: 552 (*)
Q_rsqrt: 4
Q_rsqrt result: 0.499154	Avg: 639 (*)
fsqrt   result: 0.500000	Avg: 655
Q_rsqrt: 4
Q_rsqrt result: 0.499154	Avg: 552 (*)
fsqrt   result: 0.500000	Avg: 553
Q_rsqrt: 4
Q_rsqrt result: 0.499154	Avg: 647
fsqrt   result: 0.500000	Avg: 646 (*)
Q_rsqrt: 4
Q_rsqrt result: 0.499154	Avg: 650
fsqrt   result: 0.500000	Avg: 642 (*)
Q_rsqrt: 4
Q_rsqrt result: 0.499154	Avg: 649
fsqrt   result: 0.500000	Avg: 641 (*)
Q_rsqrt: 5
Q_rsqrt result: 0.447141	Avg: 650 (*)
fsqrt   result: 0.447214	Avg: 690
Q_rsqrt: 5
Q_rsqrt result: 0.447141	Avg: 556 (*)
fsqrt   result: 0.447214	Avg: 588
Q_rsqrt: 5
Q_rsqrt result: 0.447141	Avg: 637 (*)
fsqrt   result: 0.447214	Avg: 694
Q_rsqrt: 5
Q_rsqrt result: 0.447141	Avg: 644 (*)
fsqrt   result: 0.447214	Avg: 689
Q_rsqrt: 5
Q_rsqrt result: 0.447141	Avg: 639 (*)
fsqrt   result: 0.447214	Avg: 693
Q_rsqrt: 5
Q_rsqrt result: 0.447141	Avg: 652 (*)
fsqrt   result: 0.447214	Avg: 687
Q_rsqrt: 5
Q_rsqrt result: 0.447141	Avg: 637 (*)
fsqrt   result: 0.447214	Avg: 684
Q_rsqrt: 5
Q_rsqrt result: 0.447141	Avg: 555 (*)
fsqrt   result: 0.447214	Avg: 588
Q_rsqrt: 5
Q_rsqrt result: 0.447141	Avg: 647 (*)
fsqrt   result: 0.447214	Avg: 690
Q_rsqrt: 5
Q_rsqrt result: 0.447141	Avg: 653 (*)
fsqrt   result: 0.447214	Avg: 688
Q_rsqrt: 6
Q_rsqrt result: 0.407681	Avg: 330 (*)
fsqrt   result: 0.408248	Avg: 338
Q_rsqrt: 7
Q_rsqrt result: 0.377444	Avg: 648 (*)
fsqrt   result: 0.377964	Avg: 685
Q_rsqrt: 7
Q_rsqrt result: 0.377444	Avg: 554 (*)
fsqrt   result: 0.377964	Avg: 594
Q_rsqrt: 7
Q_rsqrt result: 0.377444	Avg: 643 (*)
fsqrt   result: 0.377964	Avg: 687
Q_rsqrt: 7
Q_rsqrt result: 0.377444	Avg: 552 (*)
fsqrt   result: 0.377964	Avg: 684
Q_rsqrt: 7
Q_rsqrt result: 0.377444	Avg: 643 (*)
fsqrt   result: 0.377964	Avg: 684
Q_rsqrt: 7
Q_rsqrt result: 0.377444	Avg: 649 (*)
fsqrt   result: 0.377964	Avg: 686
Q_rsqrt: 7
Q_rsqrt result: 0.377444	Avg: 554 (*)
fsqrt   result: 0.377964	Avg: 600
Q_rsqrt: 7
Q_rsqrt result: 0.377444	Avg: 570 (*)
fsqrt   result: 0.377964	Avg: 588
Q_rsqrt: 7
Q_rsqrt result: 0.377444	Avg: 648 (*)
fsqrt   result: 0.377964	Avg: 690
Q_rsqrt: 7
Q_rsqrt result: 0.377444	Avg: 649 (*)
fsqrt   result: 0.377964	Avg: 686
Q_rsqrt: 8
Q_rsqrt result: 0.353465	Avg: 646 (*)
fsqrt   result: 0.353553	Avg: 684
Q_rsqrt: 8
Q_rsqrt result: 0.353465	Avg: 317 (*)
fsqrt   result: 0.353553	Avg: 347
Q_rsqrt: 9
Q_rsqrt result: 0.332953	Avg: 551 (*)
fsqrt   result: 0.333333	Avg: 588
Q_rsqrt: 9
Q_rsqrt result: 0.332953	Avg: 650 (*)
fsqrt   result: 0.333333	Avg: 692
Q_rsqrt: 10
Q_rsqrt result: 0.315686	Avg: 644 (*)
fsqrt   result: 0.316228	Avg: 694
Q_rsqrt: 10
Q_rsqrt result: 0.315686	Avg: 568 (*)
fsqrt   result: 0.316228	Avg: 589
Q_rsqrt: 10
Q_rsqrt result: 0.315686	Avg: 645 (*)
fsqrt   result: 0.316228	Avg: 685
Q_rsqrt: 11
Q_rsqrt result: 0.301036	Avg: 657 (*)
fsqrt   result: 0.301511	Avg: 690
Q_rsqrt: 11
Q_rsqrt result: 0.301036	Avg: 549 (*)
fsqrt   result: 0.301511	Avg: 588
Q_rsqrt: 11
Q_rsqrt result: 0.301036	Avg: 641 (*)
fsqrt   result: 0.301511	Avg: 686
Q_rsqrt: 11
Q_rsqrt result: 0.301036	Avg: 552 (*)
fsqrt   result: 0.301511	Avg: 600
Q_rsqrt: 12
Q_rsqrt result: 0.288423	Avg: 553 (*)
fsqrt   result: 0.288675	Avg: 588
Q_rsqrt: 12
Q_rsqrt result: 0.288423	Avg: 639
fsqrt   result: 0.288675	Avg: 588 (*)
Q_rsqrt: 12
Q_rsqrt result: 0.288423	Avg: 564 (*)
fsqrt   result: 0.288675	Avg: 594