// SPDX-License-Identifier: GPL-2.0-or-later

  /* mpihelp-lshift.c  -	MPI helper functions
   * Copyright (C) 1994, 1996, 1998, 2001 Free Software Foundation, Inc.
   *
   * This file is part of GnuPG.
   *

   * Note: This code is heavily based on the GNU MP Library.
   *	 Actually it's the same code with only minor changes in the
   *	 way the data is stored; this is to support the abstraction
   *	 of an optional secure memory allocation which may be used
   *	 to avoid revealing of sensitive data due to paging etc.
   *	 The GNU MP Library itself is published under the LGPL;
   *	 however I decided to publish this code under the plain GPL.
   */
  
  #include "mpi-internal.h"
  
  /* Shift U (pointed to by UP and USIZE digits long) CNT bits to the left
   * and store the USIZE least significant digits of the result at WP.
   * Return the bits shifted out from the most significant digit.
   *
   * Argument constraints:
   * 1. 0 < CNT < BITS_PER_MP_LIMB
   * 2. If the result is to be written over the input, WP must be >= UP.
   */
  
  mpi_limb_t
  mpihelp_lshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned int cnt)
  {
  	mpi_limb_t high_limb, low_limb;
  	unsigned sh_1, sh_2;
  	mpi_size_t i;
  	mpi_limb_t retval;
  
  	sh_1 = cnt;
  	wp += 1;
  	sh_2 = BITS_PER_MPI_LIMB - sh_1;
  	i = usize - 1;
  	low_limb = up[i];
  	retval = low_limb >> sh_2;
  	high_limb = low_limb;
  	while (--i >= 0) {
  		low_limb = up[i];
  		wp[i] = (high_limb << sh_1) | (low_limb >> sh_2);
  		high_limb = low_limb;
  	}
  	wp[i] = high_limb << sh_1;
  
  	return retval;
  }