// 20230102 djb: rename encrypt() as pke_encrypt()
// 20221231 djb: move encrypt.h last for macos portability; tnx thom wiggers
// 20221230 djb: add linker line

// linker define pke_encrypt

/*
  This file is for Niederreiter encryption
*/

#include "util.h"
#include "params.h"
#include "uint16_sort.h"
#include "randombytes.h"

#include <stdint.h>
#include <stdio.h>
#include <assert.h>
#include <string.h>

#include "gf.h"
#include "crypto_declassify.h"
#include "crypto_uint16.h"
#include "crypto_uint32.h"

#include "encrypt.h"

static inline crypto_uint16 uint16_is_smaller_declassify(uint16_t t,uint16_t u)
{
  crypto_uint16 mask = crypto_uint16_smaller_mask(t,u);
  crypto_declassify(&mask,sizeof mask);
  return mask;
}

static inline crypto_uint32 uint32_is_equal_declassify(uint32_t t,uint32_t u)
{
  crypto_uint32 mask = crypto_uint32_equal_mask(t,u);
  crypto_declassify(&mask,sizeof mask);
  return mask;
}

/* output: e, an error vector of weight t */
static void gen_e(unsigned char *e)
{
	int i, j, eq, count;

	union 
	{
		uint16_t nums[ SYS_T*2 ];
		unsigned char bytes[ SYS_T*2 * sizeof(uint16_t) ];
	} buf;

	uint16_t ind[ SYS_T ];
	uint64_t e_int[ (SYS_N+63)/64 ];	
	uint64_t one = 1;	
	uint64_t mask;	
	uint64_t val[ SYS_T ];	

	while (1)
	{
		randombytes(buf.bytes, sizeof(buf));

		for (i = 0; i < SYS_T*2; i++)
			buf.nums[i] = load_gf(buf.bytes + i*2);

		// moving and counting indices in the correct range

		count = 0;
		for (i = 0; i < SYS_T*2 && count < SYS_T; i++)
			if (uint16_is_smaller_declassify(buf.nums[i],SYS_N))
				ind[ count++ ] = buf.nums[i];
		
		if (count < SYS_T) continue;

		// check for repetition

		uint16_sort(ind, SYS_T);
		
		eq = 0;
		for (i = 1; i < SYS_T; i++)
			if (uint32_is_equal_declassify(ind[i-1],ind[i]))
				eq = 1;

		if (eq == 0)
			break;
	}

	for (j = 0; j < SYS_T; j++)
		val[j] = one << (ind[j] & 63);

	for (i = 0; i < (SYS_N+63)/64; i++) 
	{
		e_int[i] = 0;

		for (j = 0; j < SYS_T; j++)
		{
			mask = i ^ (ind[j] >> 6);
			mask -= 1;
			mask >>= 63;
			mask = -mask;

			e_int[i] |= val[j] & mask;
		}
	}

	for (i = 0; i < (SYS_N+63)/64 - 1; i++) 
		{ store8(e, e_int[i]); e += 8; }

	for (j = 0; j < (SYS_N % 64); j+=8) 
		e[ j/8 ] = (e_int[i] >> j) & 0xFF;
}

/* input: public key pk, error vector e */
/* output: syndrome s */
static void syndrome(unsigned char *s, const unsigned char *pk, unsigned char *e)
{
	uint64_t b;

	const uint64_t *pk_ptr; 
	const uint64_t *e_ptr = ((uint64_t *) (e + SYND_BYTES));

	int i, j;

	//

	for (i = 0; i < SYND_BYTES; i++)
		s[i] = e[i];

	for (i = 0; i < PK_NROWS; i++)	
	{
		pk_ptr = ((uint64_t *) (pk + PK_ROW_BYTES * i));
	
		b = 0;
		for (j = 0; j < PK_NCOLS/64; j++)
			b ^= pk_ptr[j] & e_ptr[j];

		b ^= ((uint32_t *) &pk_ptr[j])[0] & ((uint32_t *) &e_ptr[j])[0];

		b ^= b >> 32;
		b ^= b >> 16;
		b ^= b >> 8;
		b ^= b >> 4;
		b ^= b >> 2;
		b ^= b >> 1;
		b &= 1;

		s[ i/8 ] ^= (b << (i%8));
	}
}

/* input: public key pk */
/* output: error vector e, syndrome s */
void pke_encrypt(unsigned char *s, const unsigned char *pk, unsigned char *e)
{
	gen_e(e);

#ifdef KAT
  {
    int k;
    printf("encrypt e: positions");
    for (k = 0;k < SYS_N;++k)
      if (e[k/8] & (1 << (k&7)))
        printf(" %d",k);
    printf("\n");
  }
#endif

	syndrome(s, pk, e);
}