syr2.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_SYR2_HH
#define BLAS_SYR2_HH
 
#include "blas/util.hh"
 
#include <limits>
 
namespace blas {
 
// =============================================================================
 
template <typename TA, typename TX, typename TY>
void syr2(
    blas::Layout layout,
    blas::Uplo  uplo,
    int64_t n,
    blas::scalar_type<TA, TX, TY> alpha,
    TX const *x, int64_t incx,
    TY const *y, int64_t incy,
    TA *A, int64_t lda )
{
    typedef blas::scalar_type<TA, TX, TY> scalar_t;
 
    #define A(i_, j_) A[ (i_) + (j_)*lda ]
 
    // constants
    const scalar_t zero = 0;
 
    // check arguments
    blas_error_if( layout != Layout::ColMajor &&
                   layout != Layout::RowMajor );
    blas_error_if( uplo != Uplo::Lower &&
                   uplo != Uplo::Upper );
    blas_error_if( n < 0 );
    blas_error_if( incx == 0 );
    blas_error_if( incy == 0 );
    blas_error_if( lda < n );
 
    // quick return
    if (n == 0 || alpha == zero)
        return;
 
    // for row major, swap lower <=> upper
    if (layout == Layout::RowMajor) {
        uplo = (uplo == Uplo::Lower ? Uplo::Upper : Uplo::Lower);
    }
 
    int64_t kx = (incx > 0 ? 0 : (-n + 1)*incx);
    int64_t ky = (incy > 0 ? 0 : (-n + 1)*incy);
    if (uplo == Uplo::Upper) {
        if (incx == 1 && incy == 1) {
            // unit stride
            for (int64_t j = 0; j < n; ++j) {
                // note: NOT skipping if x[j] or y[j] is zero, for consistent NAN handling
                scalar_t tmp1 = alpha * y[j];
                scalar_t tmp2 = alpha * x[j];
                for (int64_t i = 0; i <= j; ++i) {
                    A(i, j) += x[i]*tmp1 + y[i]*tmp2;
                }
            }
        }
        else {
            // non-unit stride
            int64_t jx = kx;
            int64_t jy = ky;
            for (int64_t j = 0; j < n; ++j) {
                scalar_t tmp1 = alpha * y[jy];
                scalar_t tmp2 = alpha * x[jx];
                int64_t ix = kx;
                int64_t iy = ky;
                for (int64_t i = 0; i <= j; ++i) {
                    A(i, j) += x[ix]*tmp1 + y[iy]*tmp2;
                    ix += incx;
                    iy += incy;
                }
                jx += incx;
                jy += incy;
            }
        }
    }
    else {
        // lower triangle
        if (incx == 1 && incy == 1) {
            // unit stride
            for (int64_t j = 0; j < n; ++j) {
                scalar_t tmp1 = alpha * y[j];
                scalar_t tmp2 = alpha * x[j];
                for (int64_t i = j; i < n; ++i) {
                    A(i, j) += x[i]*tmp1 + y[i]*tmp2;
                }
            }
        }
        else {
            // non-unit stride
            int64_t jx = kx;
            int64_t jy = ky;
            for (int64_t j = 0; j < n; ++j) {
                scalar_t tmp1 = alpha * y[jy];
                scalar_t tmp2 = alpha * x[jx];
                int64_t ix = jx;
                int64_t iy = jy;
                for (int64_t i = j; i < n; ++i) {
                    A(i, j) += x[ix]*tmp1 + y[iy]*tmp2;
                    ix += incx;
                    iy += incy;
                }
                jx += incx;
                jy += incy;
            }
        }
    }
 
    #undef A
}
 
}  // namespace blas
 
#endif        //  #ifndef BLAS_SYR2_HH