nrm2.hpp

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//
// Copyright (c) 2017-2021, University of Tennessee. All rights reserved.
// Copyright (c) 2025, University of Colorado Denver. All rights reserved.
//
// This file is part of <T>LAPACK.
// <T>LAPACK is free software: you can redistribute it and/or modify it under
// the terms of the BSD 3-Clause license. See the accompanying LICENSE file.
 
#ifndef TLAPACK_BLAS_NRM2_HH
#define TLAPACK_BLAS_NRM2_HH
 
#include "tlapack/base/utils.hpp"
#include "tlapack/lapack/lassq.hpp"
 
namespace tlapack {
 
template <TLAPACK_VECTOR vector_t, disable_if_allow_optblas_t<vector_t> = 0>
auto nrm2(const vector_t& x)
{
    using real_t = real_type<type_t<vector_t> >;
 
    // scaled sum of squares
    real_t scl(1);
    real_t sumsq(0);
    lassq(x, scl, sumsq);
 
    return real_t(scl * sqrt(sumsq));
}
 
#ifdef TLAPACK_USE_LAPACKPP
 
template <TLAPACK_LEGACY_VECTOR vector_t,
          enable_if_allow_optblas_t<vector_t> = 0>
auto nrm2(vector_t const& x)
{
    // Legacy objects
    auto x_ = legacy_vector(x);
 
    // Constants to forward
    const auto& n = x_.n;
 
    return ::blas::nrm2(n, x_.ptr, x_.inc);
}
 
#endif
 
}  // namespace tlapack
 
#endif  // #ifndef TLAPACK_BLAS_NRM2_HH