| /* |
| * Written by Wilco Dijkstra, 1996. The following email exchange establishes the |
| * license. |
| * |
| * From: Wilco Dijkstra <Wilco.Dijkstra@ntlworld.com> |
| * Date: Fri, Jun 24, 2011 at 3:20 AM |
| * Subject: Re: sqrt routine |
| * To: Kevin Ma <kma@google.com> |
| * Hi Kevin, |
| * Thanks for asking. Those routines are public domain (originally posted to |
| * comp.sys.arm a long time ago), so you can use them freely for any purpose. |
| * Cheers, |
| * Wilco |
| * |
| * ----- Original Message ----- |
| * From: "Kevin Ma" <kma@google.com> |
| * To: <Wilco.Dijkstra@ntlworld.com> |
| * Sent: Thursday, June 23, 2011 11:44 PM |
| * Subject: Fwd: sqrt routine |
| * Hi Wilco, |
| * I saw your sqrt routine from several web sites, including |
| * http://www.finesse.demon.co.uk/steven/sqrt.html. |
| * Just wonder if there's any copyright information with your Successive |
| * approximation routines, or if I can freely use it for any purpose. |
| * Thanks. |
| * Kevin |
| */ |
| |
| // Minor modifications in code style for WebRTC, 2012. |
| |
| #include "common_audio/third_party/spl_sqrt_floor/spl_sqrt_floor.h" |
| |
| /* |
| * Algorithm: |
| * Successive approximation of the equation (root + delta) ^ 2 = N |
| * until delta < 1. If delta < 1 we have the integer part of SQRT (N). |
| * Use delta = 2^i for i = 15 .. 0. |
| * |
| * Output precision is 16 bits. Note for large input values (close to |
| * 0x7FFFFFFF), bit 15 (the highest bit of the low 16-bit half word) |
| * contains the MSB information (a non-sign value). Do with caution |
| * if you need to cast the output to int16_t type. |
| * |
| * If the input value is negative, it returns 0. |
| */ |
| |
| #define WEBRTC_SPL_SQRT_ITER(N) \ |
| try1 = root + (1 << (N)); \ |
| if (value >= try1 << (N)) \ |
| { \ |
| value -= try1 << (N); \ |
| root |= 2 << (N); \ |
| } |
| |
| int32_t WebRtcSpl_SqrtFloor(int32_t value) |
| { |
| int32_t root = 0, try1; |
| |
| WEBRTC_SPL_SQRT_ITER (15); |
| WEBRTC_SPL_SQRT_ITER (14); |
| WEBRTC_SPL_SQRT_ITER (13); |
| WEBRTC_SPL_SQRT_ITER (12); |
| WEBRTC_SPL_SQRT_ITER (11); |
| WEBRTC_SPL_SQRT_ITER (10); |
| WEBRTC_SPL_SQRT_ITER ( 9); |
| WEBRTC_SPL_SQRT_ITER ( 8); |
| WEBRTC_SPL_SQRT_ITER ( 7); |
| WEBRTC_SPL_SQRT_ITER ( 6); |
| WEBRTC_SPL_SQRT_ITER ( 5); |
| WEBRTC_SPL_SQRT_ITER ( 4); |
| WEBRTC_SPL_SQRT_ITER ( 3); |
| WEBRTC_SPL_SQRT_ITER ( 2); |
| WEBRTC_SPL_SQRT_ITER ( 1); |
| WEBRTC_SPL_SQRT_ITER ( 0); |
| |
| return root >> 1; |
| } |