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// 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_ROTM_HH
#define BLAS_ROTM_HH
#include "blas/util.hh"
#include <limits>
namespace blas {
// =============================================================================
/// Apply modified (fast) plane rotation, H:
/// \[
/// \begin{bmatrix} x^T \\ y^T \end{bmatrix}
/// = H
/// \begin{bmatrix} x^T \\ y^T \end{bmatrix}.
/// \]
///
/// @see rotmg to generate the rotation, and for fuller description.
///
/// Generic implementation for arbitrary data types.
///
/// @param[in] n
/// Number of elements in x and y. n >= 0.
///
/// @param[in, out] x
/// The n-element vector x, in an array of length (n-1)*abs(incx) + 1.
///
/// @param[in] incx
/// Stride between elements of x. incx must not be zero.
/// If incx < 0, uses elements of x in reverse order: x(n-1), ..., x(0).
///
/// @param[in, out] y
/// The n-element vector y, in an array of length (n-1)*abs(incy) + 1.
///
/// @param[in] incy
/// Stride between elements of y. incy must not be zero.
/// If incy < 0, uses elements of y in reverse order: y(n-1), ..., y(0).
///
/// @param[in] param
/// Array of length 5 giving parameters of modified plane rotation.
///
/// @ingroup rotm
template <typename TX, typename TY>
void rotm(
int64_t n,
TX *x, int64_t incx,
TY *y, int64_t incy,
blas::scalar_type<TX, TY> const param[5] )
{
typedef scalar_type<TX, TY> scalar_t;
// check arguments
blas_error_if( n < 0 ); // standard BLAS returns, doesn't fail
blas_error_if( incx == 0 );
blas_error_if( incy == 0 );
// quick return
if (n == 0 || param[0] == -2)
return;
if (incx == 1 && incy == 1) {
// unit stride
if (param[0] == -1) {
const scalar_t& h11 = param[1];
const scalar_t& h21 = param[2];
const scalar_t& h12 = param[3];
const scalar_t& h22 = param[4];
for (int64_t i = 0; i < n; ++i) {
scalar_t stmp = h11*x[i] + h12*y[i];
y[i] = h22*y[i] + h21*x[i];
x[i] = stmp;
}
}
else if (param[0] == 1) {
const scalar_t& h11 = param[1];
const scalar_t& h22 = param[4];
for (int64_t i = 0; i < n; ++i) {
scalar_t stmp = h11*x[i] + y[i];
y[i] = h22*y[i] - x[i];
x[i] = stmp;
}
}
else if (param[0] == 0) {
const scalar_t& h21 = param[2];
const scalar_t& h12 = param[3];
for (int64_t i = 0; i < n; ++i) {
scalar_t stmp = x[i] + h12*y[i];
y[i] = y[i] + h21*x[i];
x[i] = stmp;
}
}
else {
throw Error("Invalid param[1] in blas::rotm");
}
}
else {
// non-unit stride
int64_t ix = (incx > 0 ? 0 : (-n + 1)*incx);
int64_t iy = (incy > 0 ? 0 : (-n + 1)*incy);
if (param[0] == -1) {
const scalar_t& h11 = param[1];
const scalar_t& h21 = param[2];
const scalar_t& h12 = param[3];
const scalar_t& h22 = param[4];
for (int64_t i = 0; i < n; ++i) {
scalar_t stmp = h11*x[ix] + h12*y[iy];
y[iy] = h22*y[iy] + h21*x[ix];
x[ix] = stmp;
ix += incx;
iy += incy;
}
}
else if (param[0] == 1) {
const scalar_t& h11 = param[1];
const scalar_t& h22 = param[4];
for (int64_t i = 0; i < n; ++i) {
scalar_t stmp = h11*x[ix] + y[iy];
y[iy] = h22*y[iy] - x[ix];
x[ix] = stmp;
ix += incx;
iy += incy;
}
}
else if (param[0] == 0) {
const scalar_t& h21 = param[2];
const scalar_t& h12 = param[3];
for (int64_t i = 0; i < n; ++i) {
scalar_t stmp = x[ix] + h12*y[iy];
y[iy] = y[iy] + h21*x[ix];
x[ix] = stmp;
ix += incx;
iy += incy;
}
}
else {
throw Error("Invalid param[1] in blas::rotm");
}
}
}
} // namespace blas
#endif // #ifndef BLAS_ROTM_HH
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