text: /* This Source Code Form is subject to the terms of the Mozilla Public
   * License, v. 2.0. If a copy of the MPL was not distributed with this
   * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
  
  /* This implementation is by Ted Krovetz and was submitted to SUPERCOP and
   * marked as public domain. It was been altered to allow for non-aligned inputs
   * and to allow the block counter to be passed in specifically. */
  
  #include <string.h>
  
  #include "chacha20.h"
  
  #ifndef CHACHA_RNDS
  #define CHACHA_RNDS 20    /* 8 (high speed), 20 (conservative), 12 (middle) */
  #endif
  
  /* Architecture-neutral way to specify 16-byte vector of ints              */
  typedef unsigned vec __attribute__ ((vector_size (16)));
  
  /* This implementation is designed for Neon, SSE and AltiVec machines. The
   * following specify how to do certain vector operations efficiently on
   * each architecture, using intrinsics.
   * This implementation supports parallel processing of multiple blocks,
   * including potentially using general-purpose registers.
   */
  #if __ARM_NEON__
  #include <arm_neon.h>
  #define GPR_TOO   1
  #define VBPI      2
  #define ONE       (vec)vsetq_lane_u32(1,vdupq_n_u32(0),0)
  #define LOAD(m)   (vec)(*((vec*)(m)))
  #define STORE(m,r) (*((vec*)(m))) = (r)
  #define ROTV1(x)  (vec)vextq_u32((uint32x4_t)x,(uint32x4_t)x,1)
  #define ROTV2(x)  (vec)vextq_u32((uint32x4_t)x,(uint32x4_t)x,2)
  #define ROTV3(x)  (vec)vextq_u32((uint32x4_t)x,(uint32x4_t)x,3)
  #define ROTW16(x) (vec)vrev32q_u16((uint16x8_t)x)
  #if __clang__
  #define ROTW7(x)  (x << ((vec){ 7, 7, 7, 7})) ^ (x >> ((vec){25,25,25,25}))
  #define ROTW8(x)  (x << ((vec){ 8, 8, 8, 8})) ^ (x >> ((vec){24,24,24,24}))
  #define ROTW12(x) (x << ((vec){12,12,12,12})) ^ (x >> ((vec){20,20,20,20}))
  #else
  #define ROTW7(x)  (vec)vsriq_n_u32(vshlq_n_u32((uint32x4_t)x,7),(uint32x4_t)x,25)
  #define ROTW8(x)  (vec)vsriq_n_u32(vshlq_n_u32((uint32x4_t)x,8),(uint32x4_t)x,24)
  #define ROTW12(x) (vec)vsriq_n_u32(vshlq_n_u32((uint32x4_t)x,12),(uint32x4_t)x,20)
  #endif
  #elif __SSE2__
  #include <emmintrin.h>
  #define GPR_TOO   0
  #if __clang__
  #define VBPI      4
  #else
  #define VBPI      3
  #endif
  #define ONE       (vec)_mm_set_epi32(0,0,0,1)
  #define LOAD(m)   (vec)_mm_loadu_si128((__m128i*)(m))
  #define STORE(m,r) _mm_storeu_si128((__m128i*)(m), (__m128i) (r))
  #define ROTV1(x)  (vec)_mm_shuffle_epi32((__m128i)x,_MM_SHUFFLE(0,3,2,1))
  #define ROTV2(x)  (vec)_mm_shuffle_epi32((__m128i)x,_MM_SHUFFLE(1,0,3,2))
  #define ROTV3(x)  (vec)_mm_shuffle_epi32((__m128i)x,_MM_SHUFFLE(2,1,0,3))
  #define ROTW7(x)  (vec)(_mm_slli_epi32((__m128i)x, 7) ^ _mm_srli_epi32((__m128i)x,25))
  #define ROTW12(x) (vec)(_mm_slli_epi32((__m128i)x,12) ^ _mm_srli_epi32((__m128i)x,20))
  #if __SSSE3__
  #include <tmmintrin.h>
  #define ROTW8(x)  (vec)_mm_shuffle_epi8((__m128i)x,_mm_set_epi8(14,13,12,15,10,9,8,11,6,5,4,7,2,1,0,3))
  #define ROTW16(x) (vec)_mm_shuffle_epi8((__m128i)x,_mm_set_epi8(13,12,15,14,9,8,11,10,5,4,7,6,1,0,3,2))
  #else
  #define ROTW8(x)  (vec)(_mm_slli_epi32((__m128i)x, 8) ^ _mm_srli_epi32((__m128i)x,24))
  #define ROTW16(x) (vec)(_mm_slli_epi32((__m128i)x,16) ^ _mm_srli_epi32((__m128i)x,16))
  #endif
  #else
  #error -- Implementation supports only machines with neon or SSE2
  #endif
  
  #ifndef REVV_BE
  #define REVV_BE(x)  (x)
  #endif
  
  #ifndef REVW_BE
  #define REVW_BE(x)  (x)
  #endif
  
  #define BPI      (VBPI + GPR_TOO)  /* Blocks computed per loop iteration   */
  
  #define DQROUND_VECTORS(a,b,c,d)                \
      a += b; d ^= a; d = ROTW16(d);              \
      c += d; b ^= c; b = ROTW12(b);              \
      a += b; d ^= a; d = ROTW8(d);               \
      c += d; b ^= c; b = ROTW7(b);               \
      b = ROTV1(b); c = ROTV2(c);  d = ROTV3(d);  \
      a += b; d ^= a; d = ROTW16(d);              \
      c += d; b ^= c; b = ROTW12(b);              \
      a += b; d ^= a; d = ROTW8(d);               \
      c += d; b ^= c; b = ROTW7(b);               \
      b = ROTV3(b); c = ROTV2(c); d = ROTV1(d);
  
  #define QROUND_WORDS(a,b,c,d) \
    a = a+b; d ^= a; d = d<<16 | d>>16; \
    c = c+d; b ^= c; b = b<<12 | b>>20; \
    a = a+b; d ^= a; d = d<< 8 | d>>24; \
    c = c+d; b ^= c; b = b<< 7 | b>>25;
  
  #define WRITE_XOR(in, op, d, v0, v1, v2, v3)                \
      STORE(op + d + 0, LOAD(in + d + 0) ^ REVV_BE(v0));      \
      STORE(op + d + 4, LOAD(in + d + 4) ^ REVV_BE(v1));      \
      STORE(op + d + 8, LOAD(in + d + 8) ^ REVV_BE(v2));      \
      STORE(op + d +12, LOAD(in + d +12) ^ REVV_BE(v3));
  
  void
  ChaCha20XOR(unsigned char *out, const unsigned char *in, unsigned int inlen,
              const unsigned char key[32], const unsigned char nonce[12],
              uint32_t counter)
  {
      unsigned iters, i, *op=(unsigned *)out, *ip=(unsigned *)in, *kp;
  #if defined(__ARM_NEON__)
      unsigned *np;
  #endif
      vec s0, s1, s2, s3;
  #if !defined(__ARM_NEON__) && !defined(__SSE2__)
      __attribute__ ((aligned (16))) unsigned key[8], nonce[4];
  #endif
      __attribute__ ((aligned (16))) unsigned chacha_const[] =
          {0x61707865,0x3320646E,0x79622D32,0x6B206574};
  #if defined(__ARM_NEON__) || defined(__SSE2__)
      kp = (unsigned *)key;
  #else
      ((vec *)key)[0] = REVV_BE(((vec *)key)[0]);
      ((vec *)key)[1] = REVV_BE(((vec *)key)[1]);
      ((unsigned *)nonce)[0] = REVW_BE(((unsigned *)nonce)[0]);
      ((unsigned *)nonce)[1] = REVW_BE(((unsigned *)nonce)[1]);
      ((unsigned *)nonce)[2] = REVW_BE(((unsigned *)nonce)[2]);
      ((unsigned *)nonce)[3] = REVW_BE(((unsigned *)nonce)[3]);
      kp = (unsigned *)key;
      np = (unsigned *)nonce;
  #endif
  #if defined(__ARM_NEON__)
      np = (unsigned*) nonce;
  #endif
      s0 = LOAD(chacha_const);
      s1 = LOAD(&((vec*)kp)[0]);
      s2 = LOAD(&((vec*)kp)[1]);
      s3 = (vec) {
          counter,
          ((uint32_t*)nonce)[0],
          ((uint32_t*)nonce)[1],
          ((uint32_t*)nonce)[2]
      };
  
      for (iters = 0; iters < inlen/(BPI*64); iters++) {
  #if GPR_TOO
          register unsigned x0, x1, x2, x3, x4, x5, x6, x7, x8,
                    x9, x10, x11, x12, x13, x14, x15;
  #endif
  #if VBPI > 2
          vec v8,v9,v10,v11;
  #endif
  #if VBPI > 3
          vec v12,v13,v14,v15;
  #endif
  
          vec v0,v1,v2,v3,v4,v5,v6,v7;
          v4 = v0 = s0; v5 = v1 = s1; v6 = v2 = s2; v3 = s3;
          v7 = v3 + ONE;
  #if VBPI > 2
          v8 = v4; v9 = v5; v10 = v6;
          v11 =  v7 + ONE;
  #endif
  #if VBPI > 3
          v12 = v8; v13 = v9; v14 = v10;
          v15 = v11 + ONE;
  #endif
  #if GPR_TOO
          x0 = chacha_const[0]; x1 = chacha_const[1];
          x2 = chacha_const[2]; x3 = chacha_const[3];
          x4 = kp[0]; x5 = kp[1]; x6  = kp[2]; x7  = kp[3];
          x8 = kp[4]; x9 = kp[5]; x10 = kp[6]; x11 = kp[7];
          x12 = counter+BPI*iters+(BPI-1); x13 = np[0];
          x14 = np[1]; x15 = np[2];
  #endif
          for (i = CHACHA_RNDS/2; i; i--) {
              DQROUND_VECTORS(v0,v1,v2,v3)
              DQROUND_VECTORS(v4,v5,v6,v7)
  #if VBPI > 2
              DQROUND_VECTORS(v8,v9,v10,v11)
  #endif
  #if VBPI > 3
              DQROUND_VECTORS(v12,v13,v14,v15)
  #endif
  #if GPR_TOO
              QROUND_WORDS( x0, x4, x8,x12)
              QROUND_WORDS( x1, x5, x9,x13)
              QROUND_WORDS( x2, x6,x10,x14)
              QROUND_WORDS( x3, x7,x11,x15)
              QROUND_WORDS( x0, x5,x10,x15)
              QROUND_WORDS( x1, x6,x11,x12)
              QROUND_WORDS( x2, x7, x8,x13)
              QROUND_WORDS( x3, x4, x9,x14)
  #endif
          }
  
          WRITE_XOR(ip, op, 0, v0+s0, v1+s1, v2+s2, v3+s3)
          s3 += ONE;
          WRITE_XOR(ip, op, 16, v4+s0, v5+s1, v6+s2, v7+s3)
          s3 += ONE;
  #if VBPI > 2
          WRITE_XOR(ip, op, 32, v8+s0, v9+s1, v10+s2, v11+s3)
          s3 += ONE;
  #endif
  #if VBPI > 3
          WRITE_XOR(ip, op, 48, v12+s0, v13+s1, v14+s2, v15+s3)
          s3 += ONE;
  #endif
          ip += VBPI*16;
          op += VBPI*16;
  #if GPR_TOO
          op[0]  = REVW_BE(REVW_BE(ip[0])  ^ (x0  + chacha_const[0]));
          op[1]  = REVW_BE(REVW_BE(ip[1])  ^ (x1  + chacha_const[1]));
          op[2]  = REVW_BE(REVW_BE(ip[2])  ^ (x2  + chacha_const[2]));
          op[3]  = REVW_BE(REVW_BE(ip[3])  ^ (x3  + chacha_const[3]));
          op[4]  = REVW_BE(REVW_BE(ip[4])  ^ (x4  + kp[0]));
          op[5]  = REVW_BE(REVW_BE(ip[5])  ^ (x5  + kp[1]));
          op[6]  = REVW_BE(REVW_BE(ip[6])  ^ (x6  + kp[2]));
          op[7]  = REVW_BE(REVW_BE(ip[7])  ^ (x7  + kp[3]));
          op[8]  = REVW_BE(REVW_BE(ip[8])  ^ (x8  + kp[4]));
          op[9]  = REVW_BE(REVW_BE(ip[9])  ^ (x9  + kp[5]));
          op[10] = REVW_BE(REVW_BE(ip[10]) ^ (x10 + kp[6]));
          op[11] = REVW_BE(REVW_BE(ip[11]) ^ (x11 + kp[7]));
          op[12] = REVW_BE(REVW_BE(ip[12]) ^ (x12 + counter+BPI*iters+(BPI-1)));
          op[13] = REVW_BE(REVW_BE(ip[13]) ^ (x13 + np[0]));
          op[14] = REVW_BE(REVW_BE(ip[14]) ^ (x14 + np[1]));
          op[15] = REVW_BE(REVW_BE(ip[15]) ^ (x15 + np[2]));
          s3 += ONE;
          ip += 16;
          op += 16;
  #endif
      }
  
      for (iters = inlen%(BPI*64)/64; iters != 0; iters--) {
          vec v0 = s0, v1 = s1, v2 = s2, v3 = s3;
          for (i = CHACHA_RNDS/2; i; i--) {
              DQROUND_VECTORS(v0,v1,v2,v3);
          }
          WRITE_XOR(ip, op, 0, v0+s0, v1+s1, v2+s2, v3+s3)
          s3 += ONE;
          ip += 16;
          op += 16;
      }
  
      inlen = inlen % 64;
      if (inlen) {
          __attribute__ ((aligned (16))) vec buf[4];
          vec v0,v1,v2,v3;
          v0 = s0; v1 = s1; v2 = s2; v3 = s3;
          for (i = CHACHA_RNDS/2; i; i--) {
              DQROUND_VECTORS(v0,v1,v2,v3);
          }
  
          if (inlen >= 16) {
              STORE(op + 0, LOAD(ip + 0) ^ REVV_BE(v0 + s0));
              if (inlen >= 32) {
                  STORE(op + 4, LOAD(ip + 4) ^ REVV_BE(v1 + s1));
                  if (inlen >= 48) {
                      STORE(op + 8, LOAD(ip + 8) ^ REVV_BE(v2 + s2));
                      buf[3] = REVV_BE(v3 + s3);
                  } else {
                      buf[2] = REVV_BE(v2 + s2);
                  }
              } else {
                  buf[1] = REVV_BE(v1 + s1);
              }
          } else {
              buf[0] = REVV_BE(v0 + s0);
          }
  
          for (i=inlen & ~15; i<inlen; i++) {
              ((char *)op)[i] = ((char *)ip)[i] ^ ((char *)buf)[i];
          }
      }
  }
  