/*
  * A 32-bit implementation of the TEA algorithm
  * Copyright (c) 2015 Vesselin Bontchev
  *
  * Loosely based on the implementation of David Wheeler and Roger Needham,
  * https://en.wikipedia.org/wiki/Tiny_Encryption_Algorithm#Reference_code
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 #include "avutil.h"
 #include "common.h"
 #include "intreadwrite.h"
 #include "tea.h"
 
 typedef struct AVTEA {
     uint32_t key[16];
     int rounds;
 } AVTEA;
 
 struct AVTEA *av_tea_alloc(void)
 {
     return av_mallocz(sizeof(struct AVTEA));
 }
 
 const int av_tea_size = sizeof(AVTEA);
 
 void av_tea_init(AVTEA *ctx, const uint8_t key[16], int rounds)
 {
     int i;
 
     for (i = 0; i < 4; i++)
         ctx->key[i] = AV_RB32(key + (i << 2));
 
     ctx->rounds = rounds;
 }
 
 static void tea_crypt_ecb(AVTEA *ctx, uint8_t *dst, const uint8_t *src,
                           int decrypt, uint8_t *iv)
 {
     uint32_t v0, v1;
     int rounds = ctx->rounds;
     uint32_t k0, k1, k2, k3;
     k0 = ctx->key[0];
     k1 = ctx->key[1];
     k2 = ctx->key[2];
     k3 = ctx->key[3];
 
     v0 = AV_RB32(src);
     v1 = AV_RB32(src + 4);
 
     if (decrypt) {
         int i;
         uint32_t delta = 0x9E3779B9U, sum = delta * (rounds / 2);
 
         for (i = 0; i < rounds / 2; i++) {
             v1 -= ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3);
             v0 -= ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1);
             sum -= delta;
         }
         if (iv) {
             v0 ^= AV_RB32(iv);
             v1 ^= AV_RB32(iv + 4);
             memcpy(iv, src, 8);
         }
     } else {
         int i;
         uint32_t sum = 0, delta = 0x9E3779B9U;
 
         for (i = 0; i < rounds / 2; i++) {
             sum += delta;
             v0 += ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1);
             v1 += ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3);
         }
     }
 
     AV_WB32(dst, v0);
     AV_WB32(dst + 4, v1);
 }
 
 void av_tea_crypt(AVTEA *ctx, uint8_t *dst, const uint8_t *src, int count,
                   uint8_t *iv, int decrypt)
 {
     int i;
 
     if (decrypt) {
         while (count--) {
             tea_crypt_ecb(ctx, dst, src, decrypt, iv);
 
             src   += 8;
             dst   += 8;
         }
     } else {
         while (count--) {
             if (iv) {
                 for (i = 0; i < 8; i++)
                     dst[i] = src[i] ^ iv[i];
                 tea_crypt_ecb(ctx, dst, dst, decrypt, NULL);
                 memcpy(iv, dst, 8);
             } else {
                 tea_crypt_ecb(ctx, dst, src, decrypt, NULL);
             }
             src   += 8;
             dst   += 8;
         }
     }
 }