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
29// Minor modifications in code style for WebRTC, 2012.
30
31#include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
32
33/*
34 * Algorithm:
35 * Successive approximation of the equation (root + delta) ^ 2 = N
36 * until delta < 1. If delta < 1 we have the integer part of SQRT (N).
37 * Use delta = 2^i for i = 15 .. 0.
38 *
39 * Output precision is 16 bits. Note for large input values (close to
40 * 0x7FFFFFFF), bit 15 (the highest bit of the low 16-bit half word)
41 * contains the MSB information (a non-sign value). Do with caution
42 * if you need to cast the output to int16_t type.
43 *
44 * If the input value is negative, it returns 0.
45 */
46
47#define WEBRTC_SPL_SQRT_ITER(N)                 \
48  try1 = root + (1 << (N));                     \
49  if (value >= try1 << (N))                     \
50  {                                             \
51    value -= try1 << (N);                       \
52    root |= 2 << (N);                           \
53  }
54
55int32_t WebRtcSpl_SqrtFloor(int32_t value)
56{
57  int32_t root = 0, try1;
58
59  WEBRTC_SPL_SQRT_ITER (15);
60  WEBRTC_SPL_SQRT_ITER (14);
61  WEBRTC_SPL_SQRT_ITER (13);
62  WEBRTC_SPL_SQRT_ITER (12);
63  WEBRTC_SPL_SQRT_ITER (11);
64  WEBRTC_SPL_SQRT_ITER (10);
65  WEBRTC_SPL_SQRT_ITER ( 9);
66  WEBRTC_SPL_SQRT_ITER ( 8);
67  WEBRTC_SPL_SQRT_ITER ( 7);
68  WEBRTC_SPL_SQRT_ITER ( 6);
69  WEBRTC_SPL_SQRT_ITER ( 5);
70  WEBRTC_SPL_SQRT_ITER ( 4);
71  WEBRTC_SPL_SQRT_ITER ( 3);
72  WEBRTC_SPL_SQRT_ITER ( 2);
73  WEBRTC_SPL_SQRT_ITER ( 1);
74  WEBRTC_SPL_SQRT_ITER ( 0);
75
76  return root >> 1;
77}
78