#include <stdint.h>
#include <string.h>

// clang-format off
#define QUARTERSTEP(a, b, c, n) a += b; c ^= a; c = (c << n) | (c >> (32 - n))
#define QUARTERROUND(a, b, c, d) {\
    QUARTERSTEP(a, b, d, 16); QUARTERSTEP(c, d, b, 12); \
    QUARTERSTEP(a, b, d, 8);  QUARTERSTEP(c, d, b, 7); }

static inline uint64_t _cha_block(uint8_t* buf, size_t bufsize, uint32_t state[16], unsigned rounds) {
    unsigned blocks = bufsize / 64;
    uint32_t* out = (uint32_t*)buf;
    uint32_t x[16];
    for (unsigned b = blocks; b-->0;) {
        for (unsigned i = 0; i < 16; ++i) x[i] = state[i];  // Faster than memcpy
        for (unsigned i = rounds / 2; i-->0;) {
            // Mix columns, then diagonals
            for (unsigned j = 0; j < 4; ++j) QUARTERROUND(x[j], x[4 + j], x[8 + j], x[12 + j]);
            for (unsigned j = 0; j < 4; ++j) QUARTERROUND(x[j], x[4 + (j+1)%4], x[8 + (j+2)%4], x[12 + (j+3)%4]);
        }
        for (unsigned i = 0; i < 16; ++i) *out++ = x[i] + state[i];
        ++*(uint64_t*)(state + 12); // Increment counter
    }
    memset(x, 0, sizeof x);
    return blocks * CHA_BLOCK_SIZE;
}

#undef QUARTERROUND
#undef QUARTERSTEP