/* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 * SPDX-License-Identifier: Apache-2.0"
 *
 * Written by Nir Drucker, Shay Gueron and Dusan Kostic,
 * AWS Cryptographic Algorithms Group.
 */

#include "decode.h"
#include "decode_internal.h"
#include "utilities.h"

#define R_QWORDS_HALF_LOG2 UPTOPOW2(R_QWORDS / 2)

_INLINE_ void
rotr_big(OUT syndrome_t *out, IN const syndrome_t *in, IN size_t qw_num)
{
  // For preventing overflows (comparison in bytes)
  bike_static_assert(sizeof(*out) > 8 * (R_QWORDS + (2 * R_QWORDS_HALF_LOG2)),
                     rotr_big_err);

  *out = *in;

  for(uint32_t idx = R_QWORDS_HALF_LOG2; idx >= 1; idx >>= 1) {
    // Convert 32 bit mask to 64 bit mask
    const uint64_t mask = ((uint32_t)secure_l32_mask(qw_num, idx) + 1U) - 1ULL;
    qw_num              = qw_num - (idx & u64_barrier(mask));

    // Rotate R_QWORDS quadwords and another idx quadwords,
    // as needed by the next iteration.
    for(size_t i = 0; i < (R_QWORDS + idx); i++) {
      out->qw[i] = (out->qw[i] & u64_barrier(~mask)) |
                   (out->qw[i + idx] & u64_barrier(mask));
    }
  }
}

_INLINE_ void
rotr_small(OUT syndrome_t *out, IN const syndrome_t *in, IN const size_t bits)
{
  bike_static_assert(bits < 64, rotr_small_err);
  bike_static_assert(sizeof(*out) > (8 * R_QWORDS), rotr_small_qw_err);

  // Convert |bits| to 0/1 by using !!bits; then create a mask of 0 or
  // 0xffffffffff Use high_shift to avoid undefined behaviour when doing x << 64;
  const uint64_t mask       = (0 - (!!bits));
  const uint64_t high_shift = (64 - bits) & u64_barrier(mask);

  for(size_t i = 0; i < R_QWORDS; i++) {
    const uint64_t low_part  = in->qw[i] >> bits;
    const uint64_t high_part = (in->qw[i + 1] << high_shift) & u64_barrier(mask);
    out->qw[i]               = low_part | high_part;
  }
}

void rotate_right_port(OUT syndrome_t *out,
                       IN const syndrome_t *in,
                       IN const uint32_t    bitscount)
{
  // Rotate (64-bit) quad-words
  rotr_big(out, in, (bitscount / 64));
  // Rotate bits (less than 64)
  rotr_small(out, out, (bitscount % 64));
}

// Duplicates the first R_BITS of the syndrome three times
// |------------------------------------------|
// |  Third copy | Second copy | first R_BITS |
// |------------------------------------------|
// This is required by the rotate functions.
void dup_port(IN OUT syndrome_t *s)
{
  s->qw[R_QWORDS - 1] =
    (s->qw[0] << LAST_R_QWORD_LEAD) | (s->qw[R_QWORDS - 1] & LAST_R_QWORD_MASK);

  for(size_t i = 0; i < (2 * R_QWORDS) - 1; i++) {
    s->qw[R_QWORDS + i] =
      (s->qw[i] >> LAST_R_QWORD_TRAIL) | (s->qw[i + 1] << LAST_R_QWORD_LEAD);
  }
}

// Use half-adder as described in [1].
void bit_sliced_adder_port(OUT upc_t *upc,
                           IN OUT syndrome_t *rotated_syndrome,
                           IN const size_t    num_of_slices)
{
  // From cache-memory perspective this loop should be the outside loop
  for(size_t j = 0; j < num_of_slices; j++) {
    for(size_t i = 0; i < R_QWORDS; i++) {
      const uint64_t carry = (upc->slice[j].u.qw[i] & rotated_syndrome->qw[i]);
      upc->slice[j].u.qw[i] ^= rotated_syndrome->qw[i];
      rotated_syndrome->qw[i] = carry;
    }
  }
}

void bit_slice_full_subtract_port(OUT upc_t *upc, IN uint8_t val)
{
  // Borrow
  uint64_t br[R_QWORDS] = {0};

  for(size_t j = 0; j < SLICES; j++) {

    const uint64_t lsb_mask = 0 - (val & 0x1);
    val >>= 1;

    // Perform a - b with c as the input/output carry
    // br = 0 0 0 0 1 1 1 1
    // a  = 0 0 1 1 0 0 1 1
    // b  = 0 1 0 1 0 1 0 1
    // -------------------
    // o  = 0 1 1 0 0 1 1 1
    // c  = 0 1 0 0 1 1 0 1
    //
    // o  = a^b^c
    //            _     __    _ _   _ _     _
    // br = abc + abc + abc + abc = abc + ((a+b))c

    for(size_t i = 0; i < R_QWORDS; i++) {
      const uint64_t a      = upc->slice[j].u.qw[i];
      const uint64_t b      = lsb_mask;
      const uint64_t tmp    = ((~a) & b & (~br[i])) | ((((~a) | b) & br[i]));
      upc->slice[j].u.qw[i] = a ^ b ^ br[i];
      br[i]                 = tmp;
    }
  }
}