-rw-r--r-- 1990 libmceliece-20240812/crypto_kem/6960119/avx/vec128.c raw
// 20240805 djb: more cryptoint usage
// 20221230 djb: add linker line

// linker define vec128_mul_GF
// linker use vec128_mul_asm

#include "vec128_gf.h"
#include "crypto_int64.h"

/* input: v, an element in GF(2^m)[y]/(y^119+y^8+1) in bitsliced form */
/* input: a, an element in GF(2^m)[y]/(y^119+y^8+1) as an array of coefficients */
/* output: out, the product of v and a in bitsliced form */
void vec128_mul_GF(vec128 out[ GFBITS ], vec128 v[ GFBITS ], gf a[ SYS_T ])
{
	int i, j;
	uint64_t buf[GFBITS][4];
	vec128 prod[GFBITS];
	uint64_t p[GFBITS];

	const uint64_t allone = -1;

	// polynomial multiplication

	for (i = 0; i < GFBITS; i++)
	{
		buf[i][0] = 0;
		buf[i][1] = 0;
		buf[i][2] = 0;
		buf[i][3] = 0;
	}

	for (i = SYS_T-1; i >= 0; i--)	
	{
		for (j = 0; j < GFBITS; j++) 
		{
			buf[j][3] <<= 1;
			buf[j][3] |= crypto_int64_negative_01(buf[j][2]);
			buf[j][2] <<= 1;
			buf[j][2] |= crypto_int64_negative_01(buf[j][1]);
			buf[j][1] <<= 1;
			buf[j][1] |= crypto_int64_negative_01(buf[j][0]);
			buf[j][0] <<= 1;
		}

		vec128_mul_gf(prod, v, a[i]);

		for (j = 0; j < GFBITS; j++) 
		{
			buf[j][0] ^= vec128_extract(prod[j], 0);
			buf[j][1] ^= vec128_extract(prod[j], 1);
		}
	}
	
	// reduction modulo y^119 + y^8 + 1

	for (i = 0; i < GFBITS; i++) 
	{
		p[i] = buf[i][3];

		buf[i][2] ^= p[i] >> (SYS_T - 8 - 64);
		buf[i][1] ^= p[i] << (64 - (SYS_T - 8 - 64));
		buf[i][2] ^= p[i] >> (SYS_T - 64);
		buf[i][1] ^= p[i] << (64 - (SYS_T - 64));
	}

	//

	for (i = 0; i < GFBITS; i++) 
	{
		p[i] = buf[i][2];

		buf[i][1] ^= p[i] >> (SYS_T - 8 - 64);
		buf[i][0] ^= p[i] << (64 - (SYS_T - 8 - 64));
		buf[i][1] ^= p[i] >> (SYS_T - 64);
		buf[i][0] ^= p[i] << (64 - (SYS_T - 64));
	}

	//

	for (i = 0; i < GFBITS; i++) 
	{
		p[i] = buf[i][1] & (allone << (SYS_T - 64));

		buf[i][0] ^= p[i] >> (SYS_T - 8 - 64);
		buf[i][0] ^= p[i] >> (SYS_T - 64);
	}

	//

	for (i = 0; i < GFBITS; i++) 
		out[i] = vec128_set2x(buf[i][0], buf[i][1] & (allone >> (128 - SYS_T)));
}