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/*
* 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.
// Code optimizations for MIPS, 2013.
#include "webrtc/common_audio/signal_processing/include/signal_processing_library.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.
*/
int32_t WebRtcSpl_SqrtFloor(int32_t value)
{
int32_t root = 0, tmp1, tmp2, tmp3, tmp4;
__asm __volatile(
".set push \n\t"
".set noreorder \n\t"
"lui %[tmp1], 0x4000 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"sub %[tmp3], %[value], %[tmp1] \n\t"
"lui %[tmp1], 0x1 \n\t"
"or %[tmp4], %[root], %[tmp1] \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x4000 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 14 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x8000 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x2000 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 13 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x4000 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x1000 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 12 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x2000 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x800 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 11 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x1000 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x400 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 10 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x800 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x200 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 9 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x400 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x100 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 8 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x200 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x80 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 7 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x100 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x40 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 6 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x80 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x20 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 5 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x40 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x10 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 4 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x20 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x8 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 3 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x10 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x4 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 2 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x8 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x2 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"sll %[tmp1], 1 \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"subu %[tmp3], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x4 \n\t"
"movz %[value], %[tmp3], %[tmp2] \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
"addiu %[tmp1], $0, 0x1 \n\t"
"addu %[tmp1], %[tmp1], %[root] \n\t"
"slt %[tmp2], %[value], %[tmp1] \n\t"
"ori %[tmp4], %[root], 0x2 \n\t"
"movz %[root], %[tmp4], %[tmp2] \n\t"
".set pop \n\t"
: [root] "+r" (root), [value] "+r" (value),
[tmp1] "=&r" (tmp1), [tmp2] "=&r" (tmp2),
[tmp3] "=&r" (tmp3), [tmp4] "=&r" (tmp4)
:
);
return root >> 1;
}
|
