1
2/*============================================================================
3
4This C source file is part of the SoftFloat IEEE Floating-Point Arithmetic
5Package, Release 3e, by John R. Hauser.
6
7Copyright 2011, 2012, 2013, 2014, 2015, 2016 The Regents of the University of
8California.  All rights reserved.
9
10Redistribution and use in source and binary forms, with or without
11modification, are permitted provided that the following conditions are met:
12
13 1. Redistributions of source code must retain the above copyright notice,
14    this list of conditions, and the following disclaimer.
15
16 2. Redistributions in binary form must reproduce the above copyright notice,
17    this list of conditions, and the following disclaimer in the documentation
18    and/or other materials provided with the distribution.
19
20 3. Neither the name of the University nor the names of its contributors may
21    be used to endorse or promote products derived from this software without
22    specific prior written permission.
23
24THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS "AS IS", AND ANY
25EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
26WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ARE
27DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
28DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
29(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
30LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
31ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
32(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
33SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
34
35=============================================================================*/
36
37#include <stdint.h>
38#include "platform.h"
39
40#ifndef softfloat_approxRecipSqrt32_1
41
42extern const uint16_t softfloat_approxRecipSqrt_1k0s[];
43extern const uint16_t softfloat_approxRecipSqrt_1k1s[];
44
45uint32_t softfloat_approxRecipSqrt32_1( unsigned int oddExpA, uint32_t a )
46{
47    int index;
48    uint16_t eps, r0;
49    uint_fast32_t ESqrR0;
50    uint32_t sigma0;
51    uint_fast32_t r;
52    uint32_t sqrSigma0;
53
54    index = (a>>27 & 0xE) + oddExpA;
55    eps = (uint16_t) (a>>12);
56    r0 = softfloat_approxRecipSqrt_1k0s[index]
57             - ((softfloat_approxRecipSqrt_1k1s[index] * (uint_fast32_t) eps)
58                    >>20);
59    ESqrR0 = (uint_fast32_t) r0 * r0;
60    if ( ! oddExpA ) ESqrR0 <<= 1;
61    sigma0 = ~(uint_fast32_t) (((uint32_t) ESqrR0 * (uint_fast64_t) a)>>23);
62    r = ((uint_fast32_t) r0<<16) + ((r0 * (uint_fast64_t) sigma0)>>25);
63    sqrSigma0 = ((uint_fast64_t) sigma0 * sigma0)>>32;
64    r += ((uint32_t) ((r>>1) + (r>>3) - ((uint_fast32_t) r0<<14))
65              * (uint_fast64_t) sqrSigma0)
66             >>48;
67    if ( ! (r & 0x80000000) ) r = 0x80000000;
68    return r;
69
70}
71
72#endif
73
74