1 @ 2 @ Written by Wilco Dijkstra, 1996. The following email exchange establishes the 3 @ license. 4 @ 5 @ From: Wilco Dijkstra <Wilco.Dijkstra@ntlworld.com> 6 @ Date: Fri, Jun 24, 2011 at 3:20 AM 7 @ Subject: Re: sqrt routine 8 @ To: Kevin Ma <kma@google.com> 9 @ Hi Kevin, 10 @ Thanks for asking. Those routines are public domain (originally posted to 11 @ comp.sys.arm a long time ago), so you can use them freely for any purpose. 12 @ Cheers, 13 @ Wilco 14 @ 15 @ ----- Original Message ----- 16 @ From: "Kevin Ma" <kma@google.com> 17 @ To: <Wilco.Dijkstra@ntlworld.com> 18 @ Sent: Thursday, June 23, 2011 11:44 PM 19 @ Subject: Fwd: sqrt routine 20 @ Hi Wilco, 21 @ I saw your sqrt routine from several web sites, including 22 @ http://www.finesse.demon.co.uk/steven/sqrt.html. 23 @ Just wonder if there's any copyright information with your Successive 24 @ approximation routines, or if I can freely use it for any purpose. 25 @ Thanks. 26 @ Kevin 27 28 @ Minor modifications in code style for WebRTC, 2012. 29 @ Output is bit-exact with the reference C code in spl_sqrt_floor.c. 30 31 @ Input : r0 32 bit unsigned integer 32 @ Output: r0 = INT (SQRT (r0)), precision is 16 bits 33 @ Registers touched: r1, r2 34 35 #include "webrtc/system_wrappers/include/asm_defines.h" 36 37 GLOBAL_FUNCTION WebRtcSpl_SqrtFloor 38 .align 2 39 DEFINE_FUNCTION WebRtcSpl_SqrtFloor 40 mov r1, #3 << 30 41 mov r2, #1 << 30 42 43 @ unroll for i = 0 .. 15 44 45 cmp r0, r2, ror #2 * 0 46 subhs r0, r0, r2, ror #2 * 0 47 adc r2, r1, r2, lsl #1 48 49 cmp r0, r2, ror #2 * 1 50 subhs r0, r0, r2, ror #2 * 1 51 adc r2, r1, r2, lsl #1 52 53 cmp r0, r2, ror #2 * 2 54 subhs r0, r0, r2, ror #2 * 2 55 adc r2, r1, r2, lsl #1 56 57 cmp r0, r2, ror #2 * 3 58 subhs r0, r0, r2, ror #2 * 3 59 adc r2, r1, r2, lsl #1 60 61 cmp r0, r2, ror #2 * 4 62 subhs r0, r0, r2, ror #2 * 4 63 adc r2, r1, r2, lsl #1 64 65 cmp r0, r2, ror #2 * 5 66 subhs r0, r0, r2, ror #2 * 5 67 adc r2, r1, r2, lsl #1 68 69 cmp r0, r2, ror #2 * 6 70 subhs r0, r0, r2, ror #2 * 6 71 adc r2, r1, r2, lsl #1 72 73 cmp r0, r2, ror #2 * 7 74 subhs r0, r0, r2, ror #2 * 7 75 adc r2, r1, r2, lsl #1 76 77 cmp r0, r2, ror #2 * 8 78 subhs r0, r0, r2, ror #2 * 8 79 adc r2, r1, r2, lsl #1 80 81 cmp r0, r2, ror #2 * 9 82 subhs r0, r0, r2, ror #2 * 9 83 adc r2, r1, r2, lsl #1 84 85 cmp r0, r2, ror #2 * 10 86 subhs r0, r0, r2, ror #2 * 10 87 adc r2, r1, r2, lsl #1 88 89 cmp r0, r2, ror #2 * 11 90 subhs r0, r0, r2, ror #2 * 11 91 adc r2, r1, r2, lsl #1 92 93 cmp r0, r2, ror #2 * 12 94 subhs r0, r0, r2, ror #2 * 12 95 adc r2, r1, r2, lsl #1 96 97 cmp r0, r2, ror #2 * 13 98 subhs r0, r0, r2, ror #2 * 13 99 adc r2, r1, r2, lsl #1 100 101 cmp r0, r2, ror #2 * 14 102 subhs r0, r0, r2, ror #2 * 14 103 adc r2, r1, r2, lsl #1 104 105 cmp r0, r2, ror #2 * 15 106 subhs r0, r0, r2, ror #2 * 15 107 adc r2, r1, r2, lsl #1 108 109 bic r0, r2, #3 << 30 @ for rounding add: cmp r0, r2 adc r2, #1 110 bx lr 111
