-rw-r--r-- 3840 libmceliece-20240513/crypto_kem/8192128/vec/gf.c raw
/*
  this file is for functions for field arithmetic
*/
// 20221231 djb: const for GF_mul
// 20221230 djb: add linker line

// linker define gf_iszero gf_mul gf_inv gf_frac GF_mul

#include "gf.h"

#include "params.h"

#include <stdio.h>

/* field multiplication */
gf gf_mul(gf in0, gf in1)
{
	int i;

	uint64_t tmp;
	uint64_t t0;
	uint64_t t1;
	uint64_t t;

	t0 = in0;
	t1 = in1;

	tmp = t0 * (t1 & 1);

	for (i = 1; i < GFBITS; i++)
		tmp ^= (t0 * (t1 & (1 << i)));

	//

	t = tmp & 0x1FF0000;
	tmp ^= (t >> 9) ^ (t >> 10) ^ (t >> 12) ^ (t >> 13);

	t = tmp & 0x000E000;
	tmp ^= (t >> 9) ^ (t >> 10) ^ (t >> 12) ^ (t >> 13);

	return tmp & GFMASK;
}

/* 2 field squarings */
static inline gf gf_sq2(gf in)
{
	int i;

	const uint64_t B[] = {0x1111111111111111, 
	                      0x0303030303030303, 
	                      0x000F000F000F000F, 
	                      0x000000FF000000FF};

	const uint64_t M[] = {0x0001FF0000000000, 
	                      0x000000FF80000000, 
	                      0x000000007FC00000, 
	                      0x00000000003FE000};

	uint64_t x = in; 
	uint64_t t;

	x = (x | (x << 24)) & B[3];
	x = (x | (x << 12)) & B[2];
	x = (x | (x << 6)) & B[1];
	x = (x | (x << 3)) & B[0];

	for (i = 0; i < 4; i++)
	{
		t = x & M[i];
		x ^= (t >> 9) ^ (t >> 10) ^ (t >> 12) ^ (t >> 13);
	}

	return x & GFMASK;
}

/* square and multiply */
static inline gf gf_sqmul(gf in, gf m)
{
	int i;

	uint64_t x;
	uint64_t t0;
	uint64_t t1;
	uint64_t t;

	const uint64_t M[] = {0x0000001FF0000000,
	                      0x000000000FF80000, 
	                      0x000000000007E000}; 

	t0 = in;
	t1 = m;

	x = (t1 << 6) * (t0 & (1 << 6));
	
	t0 ^= (t0 << 7);

	x ^= (t1 * (t0 & (0x04001)));
	x ^= (t1 * (t0 & (0x08002))) << 1;
	x ^= (t1 * (t0 & (0x10004))) << 2;
	x ^= (t1 * (t0 & (0x20008))) << 3;
	x ^= (t1 * (t0 & (0x40010))) << 4;
	x ^= (t1 * (t0 & (0x80020))) << 5;

	for (i = 0; i < 3; i++)
	{
		t = x & M[i];
		x ^= (t >> 9) ^ (t >> 10) ^ (t >> 12) ^ (t >> 13);
	}

	return x & GFMASK;
}

/* square twice and multiply */
static inline gf gf_sq2mul(gf in, gf m)
{
	int i;

	uint64_t x;
	uint64_t t0;
	uint64_t t1;
	uint64_t t;

	const uint64_t M[] = {0x1FF0000000000000,
		              0x000FF80000000000, 
		              0x000007FC00000000, 
	                      0x00000003FE000000, 
	                      0x0000000001FE0000,
	                      0x000000000001E000};

	t0 = in;
	t1 = m;

	x = (t1 << 18) * (t0 & (1 << 6));

	t0 ^= (t0 << 21);

	x ^= (t1 * (t0 & (0x010000001)));
	x ^= (t1 * (t0 & (0x020000002))) << 3;
	x ^= (t1 * (t0 & (0x040000004))) << 6;
	x ^= (t1 * (t0 & (0x080000008))) << 9;
	x ^= (t1 * (t0 & (0x100000010))) << 12;
	x ^= (t1 * (t0 & (0x200000020))) << 15;

	for (i = 0; i < 6; i++)
	{
		t = x & M[i];
		x ^= (t >> 9) ^ (t >> 10) ^ (t >> 12) ^ (t >> 13);
	}

	return x & GFMASK;
}

/* return num/den */
gf gf_frac(gf den, gf num)
{
	gf tmp_11;
	gf tmp_1111;
	gf out;

	tmp_11 = gf_sqmul(den, den); // 11
	tmp_1111 = gf_sq2mul(tmp_11, tmp_11); // 1111
	out = gf_sq2(tmp_1111); 
	out = gf_sq2mul(out, tmp_1111); // 11111111
	out = gf_sq2(out);
	out = gf_sq2mul(out, tmp_1111); // 111111111111

	return gf_sqmul(out, num); // 1111111111110
}

/* return 1/den */
gf gf_inv(gf den)
{
	return gf_frac(den, ((gf) 1));
}

/* check if a == 0 */
gf gf_iszero(gf a)
{
	uint32_t t = a;

	t -= 1;
	t >>= 19;

	return (gf) t;
}

/* multiplication in GF((2^m)^t) */
void GF_mul(gf *out, const gf *in0, const gf *in1)
{
	int i, j;

	gf prod[255];

	for (i = 0; i < 255; i++)
		prod[i] = 0;

	for (i = 0; i < 128; i++)
		for (j = 0; j < 128; j++)
			prod[i+j] ^= gf_mul(in0[i], in1[j]);

	//
 
	for (i = 254; i >= 128; i--)
	{
		prod[i - 121] ^= prod[i];
		prod[i - 126] ^= prod[i];
		prod[i - 127] ^= prod[i];
		prod[i - 128] ^= prod[i];
	}

	for (i = 0; i < 128; i++)
		out[i] = prod[i];
}