/usr/include/thrust/detail/complex/csqrt.h is in libthrust-dev 1.8.1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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* Copyright 2008-2013 NVIDIA Corporation
* Copyright 2013 Filipe RNC Maia
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/*-
* Copyright (c) 2007 David Schultz <das@FreeBSD.ORG>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/*
* Adapted from FreeBSD by Filipe Maia <filipe.c.maia@gmail.com>:
* freebsd/lib/msun/src/s_csqrt.c
*/
#pragma once
#include <thrust/complex.h>
#include <thrust/detail/complex/math_private.h>
#include <cmath>
namespace thrust{
namespace detail{
namespace complex{
using thrust::complex;
__host__ __device__ inline
complex<double> csqrt(const complex<double>& z){
complex<double> result;
double a, b;
double t;
int scale;
/* We risk spurious overflow for components >= DBL_MAX / (1 + sqrt(2)). */
const double THRESH = 7.446288774449766337959726e+307;
a = z.real();
b = z.imag();
/* Handle special cases. */
if (z == 0.0)
return (complex<double>(0.0, b));
if (isinf(b))
return (complex<double>(infinity<double>(), b));
if (isnan(a)) {
t = (b - b) / (b - b); /* raise invalid if b is not a NaN */
return (complex<double>(a, t)); /* return NaN + NaN i */
}
if (isinf(a)) {
/*
* csqrt(inf + NaN i) = inf + NaN i
* csqrt(inf + y i) = inf + 0 i
* csqrt(-inf + NaN i) = NaN +- inf i
* csqrt(-inf + y i) = 0 + inf i
*/
if (signbit(a))
return (complex<double>(fabs(b - b), copysign(a, b)));
else
return (complex<double>(a, copysign(b - b, b)));
}
/*
* The remaining special case (b is NaN) is handled just fine by
* the normal code path below.
*/
// DBL_MIN*2
const double low_thresh = 4.450147717014402766180465e-308;
scale = 0;
if (fabs(a) >= THRESH || fabs(b) >= THRESH) {
/* Scale to avoid overflow. */
a *= 0.25;
b *= 0.25;
scale = 1;
}else if (fabs(a) <= low_thresh && fabs(b) <= low_thresh) {
/* Scale to avoid underflow. */
a *= 4.0;
b *= 4.0;
scale = 2;
}
/* Algorithm 312, CACM vol 10, Oct 1967. */
if (a >= 0.0) {
t = sqrt((a + hypot(a, b)) * 0.5);
result = complex<double>(t, b / (2 * t));
} else {
t = sqrt((-a + hypot(a, b)) * 0.5);
result = complex<double>(fabs(b) / (2 * t), copysign(t, b));
}
/* Rescale. */
if (scale == 1)
return (result * 2.0);
else if (scale == 2)
return (result * 0.5);
else
return (result);
}
} // namespace complex
} // namespace detail
template <typename ValueType>
__host__ __device__
inline complex<ValueType> sqrt(const complex<ValueType>& z){
return thrust::polar(std::sqrt(thrust::abs(z)),thrust::arg(z)/ValueType(2));
}
template <>
__host__ __device__
inline complex<double> sqrt(const complex<double>& z){
return detail::complex::csqrt(z);
}
} // namespace thrust
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