/* sha512.c -- FIPS 180-4 SHA-512, freestanding C99, 64-bit words only. */
#include "starkernel/sha512.h"
#include <string.h>

static const uint64_t K[80] = {
    0x428a2f98d728ae22ULL, 0x7137449123ef65cdULL, 0xb5c0fbcfec4d3b2fULL, 0xe9b5dba58189dbbcULL,
    0x3956c25bf348b538ULL, 0x59f111f1b605d019ULL, 0x923f82a4af194f9bULL, 0xab1c5ed5da6d8118ULL,
    0xd807aa98a3030242ULL, 0x12835b0145706fbeULL, 0x243185be4ee4b28cULL, 0x550c7dc3d5ffb4e2ULL,
    0x72be5d74f27b896fULL, 0x80deb1fe3b1696b1ULL, 0x9bdc06a725c71235ULL, 0xc19bf174cf692694ULL,
    0xe49b69c19ef14ad2ULL, 0xefbe4786384f25e3ULL, 0x0fc19dc68b8cd5b5ULL, 0x240ca1cc77ac9c65ULL,
    0x2de92c6f592b0275ULL, 0x4a7484aa6ea6e483ULL, 0x5cb0a9dcbd41fbd4ULL, 0x76f988da831153b5ULL,
    0x983e5152ee66dfabULL, 0xa831c66d2db43210ULL, 0xb00327c898fb213fULL, 0xbf597fc7beef0ee4ULL,
    0xc6e00bf33da88fc2ULL, 0xd5a79147930aa725ULL, 0x06ca6351e003826fULL, 0x142929670a0e6e70ULL,
    0x27b70a8546d22ffcULL, 0x2e1b21385c26c926ULL, 0x4d2c6dfc5ac42aedULL, 0x53380d139d95b3dfULL,
    0x650a73548baf63deULL, 0x766a0abb3c77b2a8ULL, 0x81c2c92e47edaee6ULL, 0x92722c851482353bULL,
    0xa2bfe8a14cf10364ULL, 0xa81a664bbc423001ULL, 0xc24b8b70d0f89791ULL, 0xc76c51a30654be30ULL,
    0xd192e819d6ef5218ULL, 0xd69906245565a910ULL, 0xf40e35855771202aULL, 0x106aa07032bbd1b8ULL,
    0x19a4c116b8d2d0c8ULL, 0x1e376c085141ab53ULL, 0x2748774cdf8eeb99ULL, 0x34b0bcb5e19b48a8ULL,
    0x391c0cb3c5c95a63ULL, 0x4ed8aa4ae3418acbULL, 0x5b9cca4f7763e373ULL, 0x682e6ff3d6b2b8a3ULL,
    0x748f82ee5defb2fcULL, 0x78a5636f43172f60ULL, 0x84c87814a1f0ab72ULL, 0x8cc702081a6439ecULL,
    0x90befffa23631e28ULL, 0xa4506cebde82bde9ULL, 0xbef9a3f7b2c67915ULL, 0xc67178f2e372532bULL,
    0xca273eceea26619cULL, 0xd186b8c721c0c207ULL, 0xeada7dd6cde0eb1eULL, 0xf57d4f7fee6ed178ULL,
    0x06f067aa72176fbaULL, 0x0a637dc5a2c898a6ULL, 0x113f9804bef90daeULL, 0x1b710b35131c471bULL,
    0x28db77f523047d84ULL, 0x32caab7b40c72493ULL, 0x3c9ebe0a15c9bebcULL, 0x431d67c49c100d4cULL,
    0x4cc5d4becb3e42b6ULL, 0x597f299cfc657e2aULL, 0x5fcb6fab3ad6faecULL, 0x6c44198c4a475817ULL
};

static inline uint64_t rotr64(uint64_t x, int n) { return (x >> n) | (x << (64 - n)); }

static void sha512_block(sha512_ctx_t *ctx, const uint8_t block[128])
{
    uint64_t w[80];
    for (int t = 0; t < 16; t++) {
        w[t] = ((uint64_t)block[t*8+0] << 56) | ((uint64_t)block[t*8+1] << 48) |
               ((uint64_t)block[t*8+2] << 40) | ((uint64_t)block[t*8+3] << 32) |
               ((uint64_t)block[t*8+4] << 24) | ((uint64_t)block[t*8+5] << 16) |
               ((uint64_t)block[t*8+6] << 8)  | ((uint64_t)block[t*8+7]);
    }
    for (int t = 16; t < 80; t++) {
        uint64_t s0 = rotr64(w[t-15], 1) ^ rotr64(w[t-15], 8) ^ (w[t-15] >> 7);
        uint64_t s1 = rotr64(w[t-2], 19) ^ rotr64(w[t-2], 61) ^ (w[t-2] >> 6);
        w[t] = w[t-16] + s0 + w[t-7] + s1;
    }

    uint64_t a = ctx->state[0], b = ctx->state[1], c = ctx->state[2], d = ctx->state[3];
    uint64_t e = ctx->state[4], f = ctx->state[5], g = ctx->state[6], h = ctx->state[7];

    for (int t = 0; t < 80; t++) {
        uint64_t S1 = rotr64(e, 14) ^ rotr64(e, 18) ^ rotr64(e, 41);
        uint64_t ch = (e & f) ^ (~e & g);
        uint64_t t1 = h + S1 + ch + K[t] + w[t];
        uint64_t S0 = rotr64(a, 28) ^ rotr64(a, 34) ^ rotr64(a, 39);
        uint64_t maj = (a & b) ^ (a & c) ^ (b & c);
        uint64_t t2 = S0 + maj;
        h = g; g = f; f = e; e = d + t1;
        d = c; c = b; b = a; a = t1 + t2;
    }

    ctx->state[0] += a; ctx->state[1] += b; ctx->state[2] += c; ctx->state[3] += d;
    ctx->state[4] += e; ctx->state[5] += f; ctx->state[6] += g; ctx->state[7] += h;
}

void sha512_init(sha512_ctx_t *ctx)
{
    ctx->state[0] = 0x6a09e667f3bcc908ULL;
    ctx->state[1] = 0xbb67ae8584caa73bULL;
    ctx->state[2] = 0x3c6ef372fe94f82bULL;
    ctx->state[3] = 0xa54ff53a5f1d36f1ULL;
    ctx->state[4] = 0x510e527fade682d1ULL;
    ctx->state[5] = 0x9b05688c2b3e6c1fULL;
    ctx->state[6] = 0x1f83d9abfb41bd6bULL;
    ctx->state[7] = 0x5be0cd19137e2179ULL;
    ctx->bitlen = 0;
    ctx->buf_len = 0;
}

void sha512_update(sha512_ctx_t *ctx, const uint8_t *data, size_t len)
{
    ctx->bitlen += (uint64_t)len * 8;
    while (len > 0) {
        size_t take = 128 - ctx->buf_len;
        if (take > len) take = len;
        memcpy(ctx->buf + ctx->buf_len, data, take);
        ctx->buf_len += take;
        data += take;
        len -= take;
        if (ctx->buf_len == 128) {
            sha512_block(ctx, ctx->buf);
            ctx->buf_len = 0;
        }
    }
}

void sha512_final(sha512_ctx_t *ctx, uint8_t out[64])
{
    uint64_t bitlen = ctx->bitlen;
    uint8_t pad = 0x80;
    sha512_update(ctx, &pad, 1);

    uint8_t zero = 0;
    while (ctx->buf_len != 112) {
        sha512_update(ctx, &zero, 1);
    }

    /* 128-bit big-endian length in bits; high 64 bits are always 0 here
     * (documented limitation in sha512.h -- no message will ever approach
     * 2^64 bits in this kernel's use). */
    uint8_t lenbuf[16] = {0};
    for (int i = 0; i < 8; i++) {
        lenbuf[15 - i] = (uint8_t)(bitlen >> (8 * i));
    }
    /* Bypass sha512_update's bitlen accounting for the length field itself
     * -- it's padding, not message content. */
    memcpy(ctx->buf + ctx->buf_len, lenbuf, 16);
    ctx->buf_len += 16;
    sha512_block(ctx, ctx->buf);
    ctx->buf_len = 0;

    for (int i = 0; i < 8; i++) {
        out[i*8+0] = (uint8_t)(ctx->state[i] >> 56);
        out[i*8+1] = (uint8_t)(ctx->state[i] >> 48);
        out[i*8+2] = (uint8_t)(ctx->state[i] >> 40);
        out[i*8+3] = (uint8_t)(ctx->state[i] >> 32);
        out[i*8+4] = (uint8_t)(ctx->state[i] >> 24);
        out[i*8+5] = (uint8_t)(ctx->state[i] >> 16);
        out[i*8+6] = (uint8_t)(ctx->state[i] >> 8);
        out[i*8+7] = (uint8_t)(ctx->state[i]);
    }
}

void sha512(const uint8_t *data, size_t len, uint8_t out[64])
{
    sha512_ctx_t ctx;
    sha512_init(&ctx);
    sha512_update(&ctx, data, len);
    sha512_final(&ctx, out);
}