#include "chacha20.h"

#define ROTL(a, b) (((a) << (b)) | ((a) >> (32 - (b))))
#define QR(a, b, c, d)                                                         \
  (a += b, d ^= a, d = ROTL(d, 16), c += d, b ^= c, b = ROTL(b, 12), a += b,   \
   d ^= a, d = ROTL(d, 8), c += d, b ^= c, b = ROTL(b, 7))
#define ROUNDS 20

void chacha_block(u32 out[16], u32 const in[16]) {
  int i;
  u32 x[16];

  for (i = 0; i < 16; ++i) {
    x[i] = in[i];
  }
  for (i = 0; i < ROUNDS; i += 2) {
    QR(x[0], x[4], x[8], x[12]);
    QR(x[1], x[5], x[9], x[13]);
    QR(x[2], x[6], x[10], x[14]);
    QR(x[3], x[7], x[11], x[15]);

    QR(x[0], x[5], x[10], x[15]);
    QR(x[1], x[6], x[11], x[12]);
    QR(x[2], x[7], x[8], x[13]);
    QR(x[3], x[4], x[9], x[14]);
  }
  for (i = 0; i < 16; ++i) {
    out[i] = x[i] + in[i];
  }
}