diff options
Diffstat (limited to 'third_party/libwebrtc/common_audio/third_party/spl_sqrt_floor/spl_sqrt_floor.c')
-rw-r--r-- | third_party/libwebrtc/common_audio/third_party/spl_sqrt_floor/spl_sqrt_floor.c | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/third_party/libwebrtc/common_audio/third_party/spl_sqrt_floor/spl_sqrt_floor.c b/third_party/libwebrtc/common_audio/third_party/spl_sqrt_floor/spl_sqrt_floor.c new file mode 100644 index 0000000000..b478a41b96 --- /dev/null +++ b/third_party/libwebrtc/common_audio/third_party/spl_sqrt_floor/spl_sqrt_floor.c @@ -0,0 +1,77 @@ +/* + * 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; +} |