-rw-r--r-- 1785 libmceliece-20240726/crypto_kem/348864/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"

/* one layer of the benes network */
static void layer(uint64_t * data, 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[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(uint64_t * r, const unsigned char * bits, int rev)
{
	int i;

	const unsigned char *cond_ptr; 
	int inc, low;

	uint64_t cond[64];

	//

	if (rev == 0) 
	{
		inc = 256;
		cond_ptr = bits;
	}
	else
	{
		inc = -256;
		cond_ptr = bits + (2*GFBITS-2)*256;
	}

	//

	transpose_64x64(r, r);

	for (low = 0; low <= 5; low++) 
	{ 
		for (i = 0; i < 64; i++) cond[i] = load4(cond_ptr + i*4);
		transpose_64x64(cond, cond);
		layer(r, cond, low); 
		cond_ptr += inc; 
	}
	
	transpose_64x64(r, r);
	
	for (low = 0; low <= 5; low++) 
	{ 
		for (i = 0; i < 32; i++) cond[i] = load8(cond_ptr + i*8);
		layer(r, cond, low); 
		cond_ptr += inc; 
	}
	for (low = 4; low >= 0; low--) 
	{ 
		for (i = 0; i < 32; i++) cond[i] = load8(cond_ptr + i*8);
		layer(r, cond, low); 
		cond_ptr += inc; 
	}

	transpose_64x64(r, r);
	
	for (low = 5; low >= 0; low--) 
	{ 
		for (i = 0; i < 64; i++) cond[i] = load4(cond_ptr + i*4);
		transpose_64x64(cond, cond);
		layer(r, cond, low); 
		cond_ptr += inc; 
	}

	transpose_64x64(r, r);
}