Source crypto/sha256.h

// SafeC Standard Library — SHA-256 / SHA-224 Hash
// Freestanding-safe.  No dynamic allocation.
// Sha256Ctx conforms to hash.h's Hasher and BlockHash (generic hashing, Hmac).
#pragma once
#include <std/crypto/buf.h>

#define SHA256_DIGEST_SIZE  32   // bytes
#define SHA224_DIGEST_SIZE  28   // bytes
#define SHA256_BLOCK_SIZE   64   // bytes

namespace std {

struct Sha256Ctx {
    unsigned int  h[8];          // current hash state
    unsigned char buf[SHA256_BLOCK_SIZE]; // partial block buffer
    unsigned long total_bytes;   // total bytes processed
    int           is224;         // 1 = SHA-224 variant

    // A fresh SHA-256 context.
    static struct Sha256Ctx new();

    // A fresh SHA-224 context (same struct, is224 = 1).
    static struct Sha256Ctx new_224();

    // Feed `len` bytes of data into the hash.
    void update([]const unsigned char data);
    // internal: the (reference, length) core of update()
    void update_n_(const &unsigned char data, unsigned long len);

    // Finalise and write the digest.
    // For SHA-256: digest must be at least 32 bytes.
    // For SHA-224: digest must be at least 28 bytes.
    void finish([]unsigned char digest);
    // internal: the (reference, length) core of finish()
    void finish_n_(&unsigned char digest);

    // 32 (SHA-256) or 28 (SHA-224) / SHA256_BLOCK_SIZE (hash.h's BlockHash).
    unsigned long digest_size() const;
    unsigned long block_size() const;
};

// Convenience: hash `len` bytes and write 32-byte digest.
void sha256([]const unsigned char data, []unsigned char digest);
// internal: the (reference, length) core of sha256()
void sha256_n_(const &unsigned char data, unsigned long len,
            &unsigned char digest);

} // namespace std