Formatted https://raw.githubusercontent.com/XKCP/XKCP/master/Standalone/CompactFIPS202/C/Keccak-more-compact.c

keccak.c

#define FOR(i, n) for (i = 0; i < n; ++i)
#define ROL(a, o) ((((u64)a) << o) ^ (((u64)a) >> (64 - o)))
#define rL(x, y) load64((u8*)s + 8 * (x + 5 * y))
#define wL(x, y, l) store64((u8*)s + 8 * (x + 5 * y), l)
#define XL(x, y, l) xor64((u8*)s + 8 * (x + 5 * y), l)

typedef unsigned char u8;
typedef unsigned long long int u64;
typedef unsigned int ui;

static void Keccak(ui r, ui c, const u8* in, u64 inLen, u8 sfx, u8* out, u64 outLen);
void shake128(const u8* in, u64 inLen, u8* out, u64 outLen) {
    Keccak(1344, 256, in, inLen, 0x1F, out, outLen);
}
void shake256(const u8* in, u64 inLen, u8* out, u64 outLen) {
    Keccak(1088, 512, in, inLen, 0x1F, out, outLen);
}
void sha3_224(const u8* in, u64 inLen, u8* out) {
    Keccak(1152, 448, in, inLen, 0x06, out, 28);
}
void sha3_256(const u8* in, u64 inLen, u8* out) {
    Keccak(1088, 512, in, inLen, 0x06, out, 32);
}
void sha3_384(const u8* in, u64 inLen, u8* out) {
    Keccak(832, 768, in, inLen, 0x06, out, 48);
}
void sha3_512(const u8* in, u64 inLen, u8* out) {
    Keccak(576, 1024, in, inLen, 0x06, out, 64);
}

static int LFSR86540(u8* R) {
    (*R) = ((*R) << 1) ^ (((*R) & 0x80) ? 0x71 : 0);
    return ((*R) & 2) >> 1;
}

static u64 load64(const u8* x) {
    ui i;
    u64 u = 0;
    FOR(i, 8) {
        u <<= 8;
        u |= x[7 - i];
    }
    return u;
}
static void store64(u8* x, u64 u) {
    ui i;
    FOR(i, 8) {
        x[i] = u;
        u >>= 8;
    }
}
static void xor64(u8* x, u64 u) {
    ui i;
    FOR(i, 8) {
        x[i] ^= u;
        u >>= 8;
    }
}

static void KeccakF1600(void* s) {
    ui r, x, y, i, j, Y;
    u8 R = 0x01;
    u64 C[5], D;
    for (i = 0; i < 24; i++) {
        /*θ*/ FOR(x, 5) C[x] = rL(x, 0) ^ rL(x, 1) ^ rL(x, 2) ^ rL(x, 3) ^ rL(x, 4);
        FOR(x, 5) {
            D = C[(x + 4) % 5] ^ ROL(C[(x + 1) % 5], 1);
            FOR(y, 5) XL(x, y, D);
        }
        /*ρπ*/ x = 1;
        y = r = 0;
        D = rL(x, y);
        FOR(j, 24) {
            r += j + 1;
            Y = (2 * x + 3 * y) % 5;
            x = y;
            y = Y;
            C[0] = rL(x, y);
            wL(x, y, ROL(D, r % 64));
            D = C[0];
        }
        /*χ*/ FOR(y, 5) {
            FOR(x, 5) C[x] = rL(x, y);
            FOR(x, 5) wL(x, y, C[x] ^ ((~C[(x + 1) % 5]) & C[(x + 2) % 5]));
        }
        /*ι*/ FOR(j, 7) if (LFSR86540(&R)) XL(0, 0, (u64)1 << ((1 << j) - 1));
    }
}
static void Keccak(ui r, ui c, const u8* in, u64 inLen, u8 sfx, u8* out, u64 outLen) {
    /*initialize*/ u8 s[200];
    ui R = r / 8;
    ui i, b = 0;
    FOR(i, 200) s[i] = 0;
    /*absorb*/ while (inLen > 0) {
        b = (inLen < R) ? inLen : R;
        FOR(i, b) s[i] ^= in[i];
        in += b;
        inLen -= b;
        if (b == R) {
            KeccakF1600(s);
            b = 0;
        }
    }
    /*pad*/ s[b] ^= sfx;
    if ((sfx & 0x80) && (b == (R - 1)))
        KeccakF1600(s);
    s[R - 1] ^= 0x80;
    KeccakF1600(s);
    /*squeeze*/ while (outLen > 0) {
        b = (outLen < R) ? outLen : R;
        FOR(i, b) out[i] = s[i];
        out += b;
        outLen -= b;
        if (outLen > 0)
            KeccakF1600(s);
    }
}