axpy.hh

// Copyright (c) 2017-2023, University of Tennessee. All rights reserved.
// SPDX-License-Identifier: BSD-3-Clause
// This program 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 BLAS_AXPY_HH
#define BLAS_AXPY_HH
 
#include "blas/util.hh"
 
#include <limits>
 
namespace blas {
 
// =============================================================================
 
template <typename TX, typename TY>
void axpy(
    int64_t n,
    blas::scalar_type<TX, TY> alpha,
    TX const *x, int64_t incx,
    TY       *y, int64_t incy )
{
    typedef blas::scalar_type<TX, TY> scalar_t;
 
    // check arguments
    blas_error_if( n < 0 );
    blas_error_if( incx == 0 );
    blas_error_if( incy == 0 );
 
    // quick return
    if (alpha == scalar_t(0))
        return;
 
    if (incx == 1 && incy == 1) {
        // unit stride
        for (int64_t i = 0; i < n; ++i) {
            y[i] += alpha*x[i];
        }
    }
    else {
        // non-unit stride
        int64_t ix = (incx > 0 ? 0 : (-n + 1)*incx);
        int64_t iy = (incy > 0 ? 0 : (-n + 1)*incy);
        for (int64_t i = 0; i < n; ++i) {
            y[iy] += alpha * x[ix];
            ix += incx;
            iy += incy;
        }
    }
}
 
}  // namespace blas
 
#endif        //  #ifndef BLAS_AXPY_HH