text: /**
   * @cond internal
   * @file shake.c
   * @copyright
   *   Uses public domain code by Mathias Panzenböck \n
   *   Uses CC0 code by David Leon Gil, 2015 \n
   *   Copyright (c) 2015 Cryptography Research, Inc.  \n
   *   Released under the MIT License.  See LICENSE.txt for license information.
   * @author Mike Hamburg
   * @brief SHA-3-n and SHAKE-n instances.
   * @warning EXPERIMENTAL!  The names, parameter orders etc are likely to change.
   */
  
  #define __STDC_WANT_LIB_EXT1__ 1 /* for memset_s */
  #define _BSD_SOURCE 1 /* for endian */
  #define _DEFAULT_SOURCE 1 /* for endian with glibc 2.20 */
  #include <assert.h>
  #include <stdint.h>
  #include <string.h>
  
  #include "portable_endian.h"
  #include "keccak_internal.h"
  #include <decaf/shake.h>
  
  #define FLAG_ABSORBING 'A'
  #define FLAG_SQUEEZING 'Z'
  
  /** Constants. **/
  static const uint8_t pi[24] = {
      10, 7,  11, 17, 18, 3, 5,  16, 8,  21, 24, 4,
      15, 23, 19, 13, 12, 2, 20, 14, 22, 9,  6,  1
  };
  
  #define RC_B(x,n) ((((x##ull)>>n)&1)<<((1<<n)-1))
  #define RC_X(x) (RC_B(x,0)|RC_B(x,1)|RC_B(x,2)|RC_B(x,3)|RC_B(x,4)|RC_B(x,5)|RC_B(x,6))
  static const uint64_t RC[24] = {
      RC_X(0x01), RC_X(0x1a), RC_X(0x5e), RC_X(0x70), RC_X(0x1f), RC_X(0x21),
      RC_X(0x79), RC_X(0x55), RC_X(0x0e), RC_X(0x0c), RC_X(0x35), RC_X(0x26),
      RC_X(0x3f), RC_X(0x4f), RC_X(0x5d), RC_X(0x53), RC_X(0x52), RC_X(0x48),
      RC_X(0x16), RC_X(0x66), RC_X(0x79), RC_X(0x58), RC_X(0x21), RC_X(0x74)
  };
  
  static inline uint64_t rol(uint64_t x, int s) {
      return (x << s) | (x >> (64 - s));
  }
  
  /* Helper macros to unroll the permutation. */
  #define REPEAT5(e) e e e e e
  #define FOR51(v, e) v = 0; REPEAT5(e; v += 1;)
  #ifndef SHAKE_NO_UNROLL_LOOPS
  #    define FOR55(v, e) v = 0; REPEAT5(e; v += 5;)
  #    define REPEAT24(e) e e e e e e e e e e e e e e e e e e e e e e e e
  #else
  #    define FOR55(v, e) for (v=0; v<25; v+= 5) { e; }
  #    define REPEAT24(e) {int _j=0; for (_j=0; _j<24; _j++) { e }}
  #endif
  
  /*** The Keccak-f[1600] permutation ***/
  void keccakf(kdomain_t state, uint8_t start_round) {
      uint64_t* a = state->w;
      uint64_t b[5] = {0}, t, u;
      uint8_t x, y, i;
      
      for (i=0; i<25; i++) a[i] = le64toh(a[i]);
  
      for (i = start_round; i < 24; i++) {
          FOR51(x, b[x] = 0; )
          FOR55(y, FOR51(x, b[x] ^= a[x + y]; ))
          FOR55(y, FOR51(x,
              a[y + x] ^= b[(x + 4) % 5] ^ rol(b[(x + 1) % 5], 1);
          ))
          // Rho and pi
          t = a[1];
          x = y = 0;
          REPEAT24(u = a[pi[x]]; y += x+1; a[pi[x]] = rol(t, y % 64); t = u; x++; )
          // Chi
          FOR55(y,
               FOR51(x, b[x] = a[y + x];)
               FOR51(x, a[y + x] = b[x] ^ ((~b[(x + 1) % 5]) & b[(x + 2) % 5]);)
          )
          // Iota
          a[0] ^= RC[i];
      }
  
      for (i=0; i<25; i++) a[i] = htole64(a[i]);
  }
  
  decaf_error_t decaf_sha3_update (
      struct decaf_keccak_sponge_s * __restrict__ decaf_sponge,
      const uint8_t *in,
      size_t len
  ) {
      assert(decaf_sponge->params->position < decaf_sponge->params->rate);
      assert(decaf_sponge->params->rate < sizeof(decaf_sponge->state));
      assert(decaf_sponge->params->flags == FLAG_ABSORBING);
      while (len) {
          size_t cando = decaf_sponge->params->rate - decaf_sponge->params->position, i;
          uint8_t* state = &decaf_sponge->state->b[decaf_sponge->params->position];
          if (cando > len) {
              for (i = 0; i < len; i += 1) state[i] ^= in[i];
              decaf_sponge->params->position += len;
              break;
          } else {
              for (i = 0; i < cando; i += 1) state[i] ^= in[i];
              dokeccak(decaf_sponge);
              len -= cando;
              in += cando;
          }
      }
      return (decaf_sponge->params->flags == FLAG_ABSORBING) ? DECAF_SUCCESS : DECAF_FAILURE;
  }
  
  decaf_error_t decaf_sha3_output (
      decaf_keccak_sponge_t decaf_sponge,
      uint8_t * __restrict__ out,
      size_t len
  ) {
      decaf_error_t ret = DECAF_SUCCESS;
      assert(decaf_sponge->params->position < decaf_sponge->params->rate);
      assert(decaf_sponge->params->rate < sizeof(decaf_sponge->state));
      
      if (decaf_sponge->params->max_out != 0xFF) {
          if (decaf_sponge->params->remaining >= len) {
              decaf_sponge->params->remaining -= len;
          } else {
              decaf_sponge->params->remaining = 0;
              ret = DECAF_FAILURE;
          }
      }
      
      switch (decaf_sponge->params->flags) {
      case FLAG_SQUEEZING: break;
      case FLAG_ABSORBING:
          {
              uint8_t* state = decaf_sponge->state->b;
              state[decaf_sponge->params->position] ^= decaf_sponge->params->pad;
              state[decaf_sponge->params->rate - 1] ^= decaf_sponge->params->rate_pad;
              dokeccak(decaf_sponge);
              decaf_sponge->params->flags = FLAG_SQUEEZING;
              break;
          }
      default:
          assert(0);
      }
      
      while (len) {
          size_t cando = decaf_sponge->params->rate - decaf_sponge->params->position;
          uint8_t* state = &decaf_sponge->state->b[decaf_sponge->params->position];
          if (cando > len) {
              memcpy(out, state, len);
              decaf_sponge->params->position += len;
              return ret;
          } else {
              memcpy(out, state, cando);
              dokeccak(decaf_sponge);
              len -= cando;
              out += cando;
          }
      }
      return ret;
  }
  
  decaf_error_t decaf_sha3_final (
      decaf_keccak_sponge_t decaf_sponge,
      uint8_t * __restrict__ out,
      size_t len
  ) {
      decaf_error_t ret = decaf_sha3_output(decaf_sponge,out,len);
      decaf_sha3_reset(decaf_sponge);
      return ret;
  }
  
  void decaf_sha3_reset (
      decaf_keccak_sponge_t decaf_sponge
  ) {
      decaf_sponge_init(decaf_sponge, decaf_sponge->params);
      decaf_sponge->params->flags = FLAG_ABSORBING;
      decaf_sponge->params->remaining = decaf_sponge->params->max_out;
  }
  
  void decaf_sponge_destroy (decaf_keccak_sponge_t decaf_sponge) { decaf_bzero(decaf_sponge, sizeof(decaf_keccak_sponge_t)); }
  
  void decaf_sponge_init (
      decaf_keccak_sponge_t decaf_sponge,
      const struct decaf_kparams_s *params
  ) {
      memset(decaf_sponge->state, 0, sizeof(decaf_sponge->state));
      decaf_sponge->params[0] = params[0];
      decaf_sponge->params->position = 0;
  }
  
  decaf_error_t decaf_sponge_hash (
      const uint8_t *in,
      size_t inlen,
      uint8_t *out,
      size_t outlen,
      const struct decaf_kparams_s *params
  ) {
      decaf_keccak_sponge_t decaf_sponge;
      decaf_sponge_init(decaf_sponge, params);
      decaf_sha3_update(decaf_sponge, in, inlen);
      decaf_error_t ret = decaf_sha3_output(decaf_sponge, out, outlen);
      decaf_sponge_destroy(decaf_sponge);
      return ret;
  }
  
  #define DEFSHAKE(n) \
      const struct decaf_kparams_s DECAF_SHAKE##n##_params_s = \
          { 0, FLAG_ABSORBING, 200-n/4, 0, 0x1f, 0x80, 0xFF, 0xFF };
      
  #define DEFSHA3(n) \
      const struct decaf_kparams_s DECAF_SHA3_##n##_params_s = \
          { 0, FLAG_ABSORBING, 200-n/4, 0, 0x06, 0x80, n/8, n/8 };
  
  size_t decaf_sponge_default_output_bytes (
      const decaf_keccak_sponge_t s
  ) {
      return (s->params->max_out == 0xFF)
          ? (200-s->params->rate)
          : ((200-s->params->rate)/2);
  }
  
  size_t decaf_sponge_max_output_bytes (
      const decaf_keccak_sponge_t s
  ) {
      return (s->params->max_out == 0xFF)
          ? SIZE_MAX
          : (size_t)((200-s->params->rate)/2);
  }
  
  DEFSHAKE(128)
  DEFSHAKE(256)
  DEFSHA3(224)
  DEFSHA3(256)
  DEFSHA3(384)
  DEFSHA3(512)
  
  /* FUTURE: Keyak instances, etc */
  