-rw-r--r-- 2846 libmceliece-20240726/crypto_kem/460896/vec/benes.c raw
/*
  This file is for Benes network related functions

  For the implementation strategy, see
  https://eprint.iacr.org/2017/793.pdf
*/
// 20221230 djb: add linker lines

// linker define benes

#include "util.h"
#include "transpose.h"
#include "params.h"
#include "benes.h"

/* middle layers of the benes network */
static void layer_in(uint64_t data[2][64], uint64_t * bits, int lgs)
{
	int i, j, s;

	uint64_t d;

	s = 1 << lgs;

	for (i = 0; i < 64; i += s*2)
	for (j = i; j < i+s; j++)
	{

		d = (data[0][j+0] ^ data[0][j+s]);
		d &= (*bits++);
		data[0][j+0] ^= d;
		data[0][j+s] ^= d;

		d = (data[1][j+0] ^ data[1][j+s]);
		d &= (*bits++);
		data[1][j+0] ^= d;
		data[1][j+s] ^= d;
	}
}

/* first and last layers of the benes network */
static void layer_ex(uint64_t * data, uint64_t * bits, int lgs)
{
	int i, j, s;

	uint64_t d;

	s = 1 << lgs;

	for (i = 0; i < 128; i += s*2)
	for (j = i; j < i+s; j++)
	{

		d = (data[j+0] ^ data[j+s]);
		d &= (*bits++);
		data[j+0] ^= d;
		data[j+s] ^= d;
	}
}

/* input: r, sequence of bits to be permuted */
/*        bits, condition bits of the Benes network */
/*        rev, 0 for normal application; !0 for inverse */
/* output: r, permuted bits */
void benes(vec * r, const unsigned char * bits, int rev)
{
	int i, iter, inc;

	const unsigned char *bits_ptr;

	uint64_t r_int_v[2][64];
	uint64_t r_int_h[2][64];
	uint64_t b_int_v[64];
	uint64_t b_int_h[64];

	//

	if (rev) { bits_ptr = bits + 12288; inc = -1024; }
	else     { bits_ptr = bits;         inc = 0;    }
		
	for (i = 0; i < 64; i++)
	{
		r_int_v[0][i] = r[i*2 + 0];
		r_int_v[1][i] = r[i*2 + 1];
	}

	transpose_64x64(r_int_h[0], r_int_v[0]);
	transpose_64x64(r_int_h[1], r_int_v[1]);

	for (iter = 0; iter <= 6; iter++)
	{
		for (i = 0; i < 64; i++)
		{
			b_int_v[i] = load8(bits_ptr); bits_ptr += 8;
		}

		bits_ptr += inc;

		transpose_64x64(b_int_h, b_int_v);
	
		layer_ex(r_int_h[0], b_int_h, iter);
	}

	transpose_64x64(r_int_v[0], r_int_h[0]);
	transpose_64x64(r_int_v[1], r_int_h[1]);

	for (iter = 0; iter <= 5; iter++) 
	{
		for (i = 0; i < 64; i++) { b_int_v[i] = load8(bits_ptr); bits_ptr += 8; }
		bits_ptr += inc;

		layer_in(r_int_v, b_int_v, iter);
	}

	for (iter = 4; iter >= 0; iter--) 
	{
		for (i = 0; i < 64; i++) { b_int_v[i] = load8(bits_ptr); bits_ptr += 8; }
		bits_ptr += inc;

		layer_in(r_int_v, b_int_v, iter);
	}

	transpose_64x64(r_int_h[0], r_int_v[0]);
	transpose_64x64(r_int_h[1], r_int_v[1]);

	for (iter = 6; iter >= 0; iter--)
	{
		for (i = 0; i < 64; i++)
		{
			b_int_v[i] = load8(bits_ptr); bits_ptr += 8;
		}

		bits_ptr += inc;

		transpose_64x64(b_int_h, b_int_v);

		layer_ex(r_int_h[0], b_int_h, iter);
	}

	transpose_64x64(r_int_v[0], r_int_h[0]);
	transpose_64x64(r_int_v[1], r_int_h[1]);

	for (i = 0; i < 64; i++)
	{
		r[i*2+0] = r_int_v[0][i];
		r[i*2+1] = r_int_v[1][i];
	}
}