/*
  This file is for Niederreiter decryption
*/
// 20240805 djb: more mask usage
// 20240503 djb: remove #ifdef KAT ... #endif
// 20221230 djb: add linker lines

// linker define decrypt
// linker use benes bm fft fft_tr
// linker use load_bits
// linker use vec256_mul_asm vec256_sq vec256_inv

#include "decrypt.h"

#include "params.h"
#include "fft_tr.h"
#include "benes.h"
#include "util.h"
#include "fft.h"
#include "bm.h"

#include "crypto_int16.h"

static void scaling(vec256 out[][GFBITS], vec256 inv[][GFBITS], const unsigned char *sk, vec256 *recv)
{
	int i, j;

	vec128 sk_int[ GFBITS ];
	vec256 eval[32][ GFBITS ];
	vec256 tmp[ GFBITS ];

	// computing inverses

	irr_load(sk_int, sk);

	fft(eval, sk_int);

	for (i = 0; i < 32; i++)
		vec256_sq(eval[i], eval[i]);

	vec256_copy(inv[0], eval[0]);

	for (i = 1; i < 32; i++)
		vec256_mul(inv[i], inv[i-1], eval[i]);

	vec256_inv(tmp, inv[31]);

	for (i = 30; i >= 0; i--)
	{
		vec256_mul(inv[i+1], tmp, inv[i]);
		vec256_mul(tmp, tmp, eval[i+1]);
	}

	vec256_copy(inv[0], tmp);
	
	//

	for (i = 0; i < 32; i++)
	for (j = 0; j < GFBITS; j++)
		out[i][j] = vec256_and(inv[i][j], recv[i]);
}

static void scaling_inv(vec256 out[][GFBITS], vec256 inv[][GFBITS], vec256 *recv)
{
	int i, j;

	for (i = 0; i < 32; i++)
	for (j = 0; j < GFBITS; j++)
		out[i][j] = vec256_and(inv[i][j], recv[i]);
}

static void preprocess(vec128 *recv, const unsigned char *s)
{
	int i;

	recv[0] = vec128_setbits(0);

	for (i = 1; i < 64; i++)
		recv[i] = recv[0];

	for (i = 0; i < SYND_BYTES/16; i++)
		recv[i] = load16(s + i*16);
}

static int weight(vec256 *v)
{
	int i, w = 0;

	for (i = 0; i < 32; i++)
	{
		w += __builtin_popcountll( vec256_extract(v[i], 0) );
		w += __builtin_popcountll( vec256_extract(v[i], 1) );
		w += __builtin_popcountll( vec256_extract(v[i], 2) );
		w += __builtin_popcountll( vec256_extract(v[i], 3) );
	}

	return w;
}

static uint64_t synd_cmp(vec256 *s0 , vec256 *s1)
{
	int i;
	vec256 diff;

	diff = vec256_xor(s0[0], s1[0]);

	for (i = 1; i < GFBITS; i++)
		diff = vec256_or(diff, vec256_xor(s0[i], s1[i]));
	
	return vec256_testz(diff);
}

static void reformat_128to256(vec256 * out, vec128 * in)
{
	int i;
	uint64_t v[4];

	for (i = 0; i < 32; i++)
	{
		v[0] = vec128_extract(in[2*i+0], 0);
		v[1] = vec128_extract(in[2*i+0], 1);
		v[2] = vec128_extract(in[2*i+1], 0);
		v[3] = vec128_extract(in[2*i+1], 1);

		out[i] = vec256_set4x(v[0], v[1], v[2], v[3]);
	}
}

static void reformat_256to128(vec128 * out, vec256 * in)
{
	int i;
	uint64_t v[4];

	for (i = 0; i < 32; i++)
	{
		v[0] = vec256_extract(in[i], 0);
		v[1] = vec256_extract(in[i], 1);
		v[2] = vec256_extract(in[i], 2);
		v[3] = vec256_extract(in[i], 3);

		out[2*i+0] = vec128_set2x(v[0], v[1]);
		out[2*i+1] = vec128_set2x(v[2], v[3]);
	}
}

/* Niederreiter decryption with the Berlekamp decoder */
/* intput: sk, secret key */
/*         s, ciphertext (syndrome) */
/* output: e, error vector */
/* return: 0 for success; 1 for failure */
int decrypt(unsigned char *e, const unsigned char *sk, const unsigned char *s)
{
	int i;
	
	uint16_t check_synd;
	uint16_t check_weight;

	vec256 inv[ 64 ][ GFBITS ];
	vec256 scaled[ 64 ][ GFBITS ];
	vec256 eval[ 64 ][ GFBITS ];

	vec128 error128[ 64 ];
	vec256 error256[ 32 ];

	vec256 s_priv[ GFBITS ];
	vec256 s_priv_cmp[ GFBITS ];
	vec128 locator[ GFBITS ];

	vec128 recv128[ 64 ];
	vec256 recv256[ 32 ];
	vec256 allone;

	vec128 bits_int[25][32];

	// Berlekamp decoder

	preprocess(recv128, s);

	load_bits(bits_int, sk + IRR_BYTES);
	benes(recv128, bits_int, 1); 
	reformat_128to256(recv256, recv128);

	scaling(scaled, inv, sk, recv256); // scaling
	fft_tr(s_priv, scaled); // transposed FFT
	bm(locator, s_priv); // Berlekamp Massey

	fft(eval, locator); // FFT

	// reencryption and weight check

	allone = vec256_set1_16b(0xFFFF);

	for (i = 0; i < 32; i++)
	{
		error256[i] = vec256_or_reduce(eval[i]);
		error256[i] = vec256_xor(error256[i], allone);
	}

	check_weight = weight(error256) ^ SYS_T;
	check_weight = crypto_int16_zero_01(check_weight);

	scaling_inv(scaled, inv, error256);
	fft_tr(s_priv_cmp, scaled);

	check_synd = synd_cmp(s_priv, s_priv_cmp);

	//

	reformat_256to128(error128, error256);
	benes(error128, bits_int, 0);

	for (i = 0; i < 64; i++)
		store16(e + i*16, error128[i]);

	return 1 - (check_synd & check_weight);
}