/* =============================================================================
 * sha256_sw.c - 자급식 SHA-256 (FIPS 180-4)
 *
 * 공개 도메인 구현(Brad Conte 계열)을 stdint 기반으로 정리한 것.
 * 외부 의존성 없음 → 펌웨어 서명 및 호스트/ARM 컴파일 게이트에서 그대로 사용.
 * 정확성은 sha256_selftest()의 NIST 표준 벡터로 부팅 시 검증할 수 있다.
 * ===========================================================================*/
#include "sha256_backend.h"
#include <string.h>

#define ROTR(a, b) (((a) >> (b)) | ((a) << (32 - (b))))
#define CH(x, y, z)  (((x) & (y)) ^ (~(x) & (z)))
#define MAJ(x, y, z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
#define EP0(x)  (ROTR(x, 2) ^ ROTR(x, 13) ^ ROTR(x, 22))
#define EP1(x)  (ROTR(x, 6) ^ ROTR(x, 11) ^ ROTR(x, 25))
#define SIG0(x) (ROTR(x, 7) ^ ROTR(x, 18) ^ ((x) >> 3))
#define SIG1(x) (ROTR(x, 17) ^ ROTR(x, 19) ^ ((x) >> 10))

static const uint32_t K[64] = {
    0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1,
    0x923f82a4, 0xab1c5ed5, 0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
    0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174, 0xe49b69c1, 0xefbe4786,
    0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
    0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147,
    0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
    0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85, 0xa2bfe8a1, 0xa81a664b,
    0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
    0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a,
    0x5b9cca4f, 0x682e6ff3, 0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
    0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
};

static void sha256_transform(sha256_ctx *ctx, const uint8_t data[64])
{
    uint32_t a, b, c, d, e, f, g, h, t1, t2, m[64];
    int i, j;

    for (i = 0, j = 0; i < 16; i++, j += 4) {
        m[i] = ((uint32_t)data[j] << 24) | ((uint32_t)data[j + 1] << 16) |
               ((uint32_t)data[j + 2] << 8) | ((uint32_t)data[j + 3]);
    }
    for (; i < 64; i++) {
        m[i] = SIG1(m[i - 2]) + m[i - 7] + SIG0(m[i - 15]) + m[i - 16];
    }

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

    for (i = 0; i < 64; i++) {
        t1 = h + EP1(e) + CH(e, f, g) + K[i] + m[i];
        t2 = EP0(a) + MAJ(a, b, c);
        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 sha256_init(sha256_ctx *ctx)
{
    ctx->bitlen = 0;
    ctx->buflen = 0;
    ctx->state[0] = 0x6a09e667; ctx->state[1] = 0xbb67ae85;
    ctx->state[2] = 0x3c6ef372; ctx->state[3] = 0xa54ff53a;
    ctx->state[4] = 0x510e527f; ctx->state[5] = 0x9b05688c;
    ctx->state[6] = 0x1f83d9ab; ctx->state[7] = 0x5be0cd19;
}

void sha256_update(sha256_ctx *ctx, const uint8_t *data, size_t len)
{
    for (size_t i = 0; i < len; i++) {
        ctx->buffer[ctx->buflen++] = data[i];
        if (ctx->buflen == 64) {
            sha256_transform(ctx, ctx->buffer);
            ctx->bitlen += 512;
            ctx->buflen = 0;
        }
    }
}

void sha256_final(sha256_ctx *ctx, uint8_t out[SHA256_DIGEST_LEN])
{
    uint32_t i = ctx->buflen;

    ctx->bitlen += (uint64_t)ctx->buflen * 8;

    /* 패딩: 0x80, 그리고 길이(64비트 빅엔디언)가 들어갈 자리까지 0 */
    ctx->buffer[i++] = 0x80;
    if (i > 56) {
        while (i < 64) ctx->buffer[i++] = 0x00;
        sha256_transform(ctx, ctx->buffer);
        i = 0;
    }
    while (i < 56) ctx->buffer[i++] = 0x00;

    for (int b = 7; b >= 0; b--) {
        ctx->buffer[56 + (7 - b)] = (uint8_t)(ctx->bitlen >> (b * 8));
    }
    sha256_transform(ctx, ctx->buffer);

    for (i = 0; i < 8; i++) {
        out[i * 4 + 0] = (uint8_t)(ctx->state[i] >> 24);
        out[i * 4 + 1] = (uint8_t)(ctx->state[i] >> 16);
        out[i * 4 + 2] = (uint8_t)(ctx->state[i] >> 8);
        out[i * 4 + 3] = (uint8_t)(ctx->state[i]);
    }
}

void sha256(const uint8_t *data, size_t len, uint8_t out[SHA256_DIGEST_LEN])
{
    sha256_ctx ctx;
    sha256_init(&ctx);
    sha256_update(&ctx, data, len);
    sha256_final(&ctx, out);
}