c4fb4e38de
Corresponds to upstream commit 524e9b043e7e86fd72353b987c9d5f6a1ebf83e1 Update notes: * Moved src/ to webrtc/ to easily diff against the third_party/webrtc in the chromium tree * ARM/NEON/MIPS support is not yet hooked up * Tests have not been copied
78 lines
2.4 KiB
C
78 lines
2.4 KiB
C
/*
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* Written by Wilco Dijkstra, 1996. The following email exchange establishes the
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* license.
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*
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* From: Wilco Dijkstra <Wilco.Dijkstra@ntlworld.com>
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* Date: Fri, Jun 24, 2011 at 3:20 AM
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* Subject: Re: sqrt routine
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* To: Kevin Ma <kma@google.com>
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* Hi Kevin,
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* Thanks for asking. Those routines are public domain (originally posted to
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* comp.sys.arm a long time ago), so you can use them freely for any purpose.
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* Cheers,
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* Wilco
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*
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* ----- Original Message -----
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* From: "Kevin Ma" <kma@google.com>
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* To: <Wilco.Dijkstra@ntlworld.com>
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* Sent: Thursday, June 23, 2011 11:44 PM
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* Subject: Fwd: sqrt routine
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* Hi Wilco,
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* I saw your sqrt routine from several web sites, including
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* http://www.finesse.demon.co.uk/steven/sqrt.html.
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* Just wonder if there's any copyright information with your Successive
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* approximation routines, or if I can freely use it for any purpose.
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* Thanks.
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* Kevin
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*/
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// Minor modifications in code style for WebRTC, 2012.
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#include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
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/*
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* Algorithm:
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* Successive approximation of the equation (root + delta) ^ 2 = N
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* until delta < 1. If delta < 1 we have the integer part of SQRT (N).
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* Use delta = 2^i for i = 15 .. 0.
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*
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* Output precision is 16 bits. Note for large input values (close to
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* 0x7FFFFFFF), bit 15 (the highest bit of the low 16-bit half word)
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* contains the MSB information (a non-sign value). Do with caution
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* if you need to cast the output to int16_t type.
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*
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* If the input value is negative, it returns 0.
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*/
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#define WEBRTC_SPL_SQRT_ITER(N) \
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try1 = root + (1 << (N)); \
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if (value >= try1 << (N)) \
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{ \
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value -= try1 << (N); \
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root |= 2 << (N); \
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}
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int32_t WebRtcSpl_SqrtFloor(int32_t value)
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{
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int32_t root = 0, try1;
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WEBRTC_SPL_SQRT_ITER (15);
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WEBRTC_SPL_SQRT_ITER (14);
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WEBRTC_SPL_SQRT_ITER (13);
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WEBRTC_SPL_SQRT_ITER (12);
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WEBRTC_SPL_SQRT_ITER (11);
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WEBRTC_SPL_SQRT_ITER (10);
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WEBRTC_SPL_SQRT_ITER ( 9);
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WEBRTC_SPL_SQRT_ITER ( 8);
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WEBRTC_SPL_SQRT_ITER ( 7);
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WEBRTC_SPL_SQRT_ITER ( 6);
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WEBRTC_SPL_SQRT_ITER ( 5);
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WEBRTC_SPL_SQRT_ITER ( 4);
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WEBRTC_SPL_SQRT_ITER ( 3);
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WEBRTC_SPL_SQRT_ITER ( 2);
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WEBRTC_SPL_SQRT_ITER ( 1);
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WEBRTC_SPL_SQRT_ITER ( 0);
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return root >> 1;
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}
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